EP1161507A1

EP1161507A1 - Soluble adhesives

Info

Publication number: EP1161507A1
Application number: EP00909120A
Authority: EP
Inventors: Christian Kirsten; Andreas Ferencz; Michael Hirthammer
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 1999-02-08
Filing date: 2000-01-29
Publication date: 2001-12-12
Also published as: BR0008038A; ZA200106456B; TR200101933T2; JP2002536527A; MXPA01007993A; CA2362502A1; AU3151100A; CZ20012877A3; WO2000047686A1; DE19904835A1

Abstract

Soluble adhesives are formulated on the basis of binding agents which have at least one structural component that contains di- or polysulfide bonds. These adhesives can be hardened according to conventional methods as either two-component adhesives or one-component heat-hardening adhesives. Adhesive compounds of this type can be re-dissolved with non-dispersed mercapto compound-based or reducing agent-based splitting agents which are inert at room temperature, optionally with the addition of catalysts. This enables structural parts which have been glued together to be separated in the glue line by chemical means.

Description

Removable adhesives

The present invention relates to adhesive compositions based on binders which contain di- or polysulfide bonds and are suitable for producing releasable adhesive bonds. The present invention further relates to cleavage reagents for detaching adhesive bonds and a method for producing and detaching adhesive bonds.

In many branches of industry, in particular in the metalworking industry, e.g. In the automotive industry, in commercial vehicle construction and their supplier industries, or also in the manufacture of machines and household appliances or also in the construction industry, the same or different metallic and non-metallic substrates are increasingly bonded to one another in an adhesive or sealing manner. This type of joining of components is increasingly replacing classic joining methods such as riveting, screwing or welding, because gluing / sealing offers a variety of technological advantages. In contrast to the traditional joining methods such as welding, riveting, screwing, the loosening and separation of glued components has not yet been satisfactorily solved.

EP-A-735121 describes an adhesive film section for a residue-free and damage-free and releasable adhesive bond consisting of a double-sided adhesive film with a handle protruding from the adhesive film, to which pulling in the direction of the Bonding level the bond is detachable. However, this method can only be used if the adhesive layer of the adhesive film is a pressure sensitive adhesive. With such adhesive connections, however, only slight tension or Achieve peel strengths, so that this method can only be used for fixing small objects such as hooks and the like in the household area.

DE-A-4230116 describes a rubber composition containing a blend of an aliphatic polyol with an aromatic dianhydride. This adhesive composition enables the bond to be dissolved in aqueous alkaline systems, specifically called soda solutions or alkali solutions. It is proposed to use these aqueous alkaline-soluble adhesives for the rational production of magnetic parts and other small parts, the adhesive only being used for the production of auxiliary pushings in material processing. Very similar adhesives are also known as labeling adhesives, which allow the labels to be peeled off in an aqueous or aqueous alkaline environment in beverage bottles and similar containers.

DE-A-4328108 describes an adhesive for floor coverings and a method for detaching these bonded floor coverings with the aid of microwave energy. For this purpose, the adhesive should be electrically conductive and softenable by a microwave device. Solvent-free contact adhesives based on (aqueous) polymer dispersions containing copper powder or aluminum powder are specifically proposed. According to the teaching of this document, the glued pieces of floor covering are to be placed in a microwave device to release the adhesive connection, so that the adhesive layer can be softened, so that the pieces of floor covering can be removed manually after the adhesive layer has softened. WO 94/12582 describes a pressure sensitive adhesive based on a mixture of an aqueous polymer dispersion and an adhesive dissolved in an organic solvent, as well as tackifiers and production agents. This pressure sensitive adhesive has a constant adhesive force over a wide temperature range and enables mechanical separation of the adhesive bonds. It is stated that these adhesive connections are suitable for bonding insulation and / or decorative surface parts such as insulation materials or plastic films.

EP-A-521825 describes a releasable adhesive connection in which the parts connected to one another are joined by means of an adhesive bead inserted between them. This bead of adhesive contains a flat thermoplastic separating element. When the adhesive connection is heated by current or radiation supply, this thermoplastic separating layer is softened, so that the parts connected to one another can be mechanically separated from one another. Specifically, EP-A-521825 suggests using such releasable adhesive bonds in direct glazing in vehicle construction.

DE-A-19526351 describes a solvent gel for lacquers, paints and adhesives based on organic solvents with the addition of network thickeners and other conventional agents. The use as a stripping agent in the stripping of 2-component lacquers is mentioned as a concrete field of application. Although it is mentioned that such mixtures are also suitable for use with 2-component adhesives, there is no concrete information on how to loosen such adhesive connections. Similarly, WO 87/01724 describes a composition for removing cured polysulfide sealants or coatings. Here are in one Solvent or solvent mixture consisting of dimethylformamide or dimethylacetamide or their mixture with aromatic solvents such as toluene or xylene, an alkali metal or ammonium thiolate based on alkyl or phenyl thiolates and applied to hardened polysulfide sealants or coating materials, in order to then remove them from their substrates, such as e.g. B. To be able to remove aircraft tanks. No information is given on loosening adhesive bonds.

WO 97/00283 describes a method for reprocessing cured or partially cured polysulfide and / or polymer captan compositions. Here, hardened polysulfide materials are depolymerized in a solution of a depolymerization agent based on vulcanization accelerators in a non-volatile liquid, in order to be subsequently reused as a component of a hardener component of 2-component polysulfide and / or polymercaptan adhesives / sealants or coating materials become. Evidence of a loosening of adhesive bonds by this method is not disclosed.

In the work "Reversible Crosslinking in Epoxy Resins", Journal of Applied Polymer Science, 39, 1439 to 1457 (1990) VR Sastri and GC Tesoro describe epoxy resins with different epoxy equivalents which are crosslinked with 4,4'-dithioaniline "Paint the crosslinked resin into 600 µm particles. This finely ground powder is then refluxed in a solution of diglyme, hydrochloric acid and tributylphosphine until the ground resin is dissolved. Analogous disclosures are made in US-A-4,882,399 Authors made. Concrete information about detachable adhesive connections is missing in both documents.

The detachable adhesive connections described in the abovementioned prior art are each to be used only in a very narrowly limited field of application, in particular there are no adhesive compositions which combine the easy and quick detachability or easy removal of the adhesive connection with high strength of the bond and stability against external influences .

The as yet unpublished PCT / EP 98/04667 describes adhesives in which at least one structural component contains di- or polysulfide bonds and which can be dissolved again after curing by applying solutions of cleavage agents based on mercapto compounds. This makes it possible to chemically separate bonded components in the adhesive joint. According to the teaching of this document, the cleavage agent can also be admixed in a form of the adhesive formulation which is inert at room temperature, it being possible for the cleavage to take place at an elevated temperature after activation of the reagent. No specific formations of this inert form of the splitting agent are mentioned. Although the use of solvent-containing cleavage agents makes it possible to detach adhesive bonds again, it is desirable to be able to do without solvent-based cleavage agents since this procedure

• is very time-consuming due to the diffusion-induced exposure time of the cleavage agents

• The handling of solvent-containing cleavage agents should be avoided for environmental reasons. The object was therefore to provide adhesive compositions which can be detached again when required and in which the use of externally applied solvent-containing cleavage agents can be avoided.

The solution to the problem can be found in the patent claims. It is based essentially on the provision of adhesive compositions based on binders which contain at least one di- or polysulfide bond per molecule and which contain a cleavage agent in the adhesive composition which is inert at room temperature or use temperature, which is at suitable activation, however, is able to release these di- or polysulfide bonds, in order to enable the parts to be separated.

Here, "inert at room temperature or use temperature" with respect to the cleavage agent means that this cleavage agent is dispersed in the adhesive matrix at room temperature or the use temperature of the bonded unit, but cannot cause cleavage of the di- or polysulfide bonds of the adhesive matrix in this temperature range Rather, this cleavage and thus loosening of the adhesive connection should only take place after a triggering step, ie after the activation of the cleavage reagent.

Another object of the present invention is a method for producing and releasing adhesive bonds with the following essential process steps:

• Joining and connecting the parts with the aid of an adhesive composition, the binder of which contains at least one structural component which contains at least one di- or polysulfide bond per molecule. There- At, this adhesive composition can be a one-component system that the user can apply directly without mixing components. However, the adhesive system can also consist of 2 or more components to be stored separately, which are only mixed with one another immediately before application.

Curing of the adhesive at room temperature, i.e. by reaction of the individual components with one another in the case of multi-component systems or by reaction of the single-component system with atmospheric moisture and / or atmospheric oxygen. Other options for curing are the supply of heat, UV light or electron beams. The curing process depends on the crosslinking mechanism of the components.

• The adhesive connection is loosened by activating the cleaving reagent dispersed in the adhesive mixture.

• If necessary, this separation process can be further accelerated by heating the bonded component or the bond point.

If necessary, the separation of the bonded components can be further accelerated by mechanical stress on the adhesive joint.

Substantial constituents of the structural components of the binder according to the invention are therefore compounds which have at least one disulfide or polysulfide bond of the general formula

XR ¹ -S _x -R ² -Y (I) contain. Herein R ¹ and R ^{2 are} divalent alkyl and / or aryl residues, in the simplest case a C ₂ to C ₈ alkylene group or a divalent aromatic residue such as 1,2-, 1,3- or 1,4-phenylene , Diphenylene, naphthylene or similar aromatic radicals. X and Y can independently of one another denote any functional group capable of reaction, preference being given to primary or secondary amino groups, hydroxyl groups, carboxyl groups. In addition, X and / or Y can be mercapto groups, epoxy groups, isocyanate groups, alkoxysilyl groups or also olefinic double bonds, in the latter case R ¹ and / or R ^{2 can be} replaced by a covalent bond, x is an integer in the range between 2 and 8, 2 is particularly preferred.

Examples of structural components according to formula I which contain olefinic double bonds can be prepared in the following way: In a first step, dithiodial alcohols or dithiodiamines are reacted with diisocyanates in such a way that isocyanate-terminated disulfide compounds result, ie the diisocyanate component is converted into a stoichiometric one Excess over the dithiodial alcohol or dithiodiamine component used. In a second step, these NCO-terminated disulfide compounds are reacted with hydroxyalkyl acrylates or hydroxyalkyl methacrylates, so that (meth) acrylate-terminated disulfide compounds are formed. Examples of the hydroxyalkyl (meth) acrylates to be used are the corresponding ethyl, propyl or butyl compounds. The (meth) acrylate-terminated disulfide compounds obtained in this way can be combined as usual with corresponding copolymerizable compounds and cured by free radical or ionic means. Examples of such copolymerizable compounds known per se are given in DE-C 19545123 column 5 lines 24 to 47. The comonomers mentioned therein are expressly part of this invention.

In an analogous manner, epoxy-functionalized di- or polysulfides can be prepared from the NCO-terminated disulfide or polysulfide compounds by reaction with epoxy compounds containing hydroxyl groups. Examples of such hydroxy-functional epoxides are glycidol and the various glycidyl ethers of bisphenol A, which generally carry free hydroxyl groups.

Analogously, it is possible, by reacting COOH-terminated disulfide or polysulfide compounds with di- or polyfunctional epoxy compounds, to obtain epoxy-functionalized di- or polysulfide compounds.

The corresponding alkoxysilane-terminated products can be prepared from the NCO-terminated di- or polysulfide compounds by reaction with amino-functional alkoxysilanes.

Very particularly preferred structural components according to formula I are cystamine, dithiodiethanol and dithiodipropionic acid.

One or more compounds of the general formula can be used as a further structural component of the adhesive composition according to the invention

XR ³ -Y (II) Find use, where X and Y can have the meanings given above and R ^{3 is} an at least divalent organic radical. The components of the formula II are usually so-called prepolymer compounds with a molecular weight range between 300 and 20,000, preferably between 700 and 10,000.

Particularly preferred components according to formula II are epoxy resins, isocyanate group-containing polyurethane prepolymers, novolak resins, phenolic resins or unsaturated polyesters. However, the above-mentioned copolymerizable olefinically unsaturated compounds can also take the place of the components according to formula II.

A large number of polyglycidyl ethers of polyols such as ethylene glycol, dithylene glycol, triethylene glycol, 1, 2-propylene glycol, 1, 5-pentanediol, 1, 2,6-hexanetriol, glycerol, 2,2-bis (4- hydroxycyclohexyl) propane and polyalkylene glycols such as polypropylene glycol. The polyglycidyl esters of aliphatic or aromatic polycarboxylic acids, such as oxalic acid, succinic acid, glutaric acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid and dimer fatty acid, are also suitable. Other suitable epoxy compounds are the polyglycidyl ethers of polyphenols such as bisphenol A, 1,1-bis (4-hydroxyphenyl) ethane, 1,1-bis (4-hydroxyphenyl) isobutane, 1,5-dihydroxynaphthalene and novolak resins. Preferred epoxy compounds include higher molecular weight resins such as the chain-extended diglycidyl ether of bisphenol A, diglycidyl ether of dimer fatty acid-extended bisphenol A and bisphenol A glycidyl ether-terminated polyether polyurethanes. The adducts of epoxy resins with carboxy-, amino- and / or hydroxy-functional nitrile rubbers (Hycar types) can also be used as the epoxy component. The polyurethane prepolymers containing isocyanate groups are composed of aromatic, cycloaliphatic or aliphatic polyisocyanates and di- and / or polyols.

Examples of suitable aromatic polyisocyanates are: All isomers of tolylene diisocyanate (TDI) either in isomerically pure form or as a mixture of several isomers, naphthalene-1,5-diisocyanate, diphenylmethane-4,4'-diisocyanate (MDI), diphenylmethane-2,4 ' Diisocyanate and mixtures of 4,4'-diphenylmethane diisocyanate with the 2,4'-isomer or their mixtures with higher-functional oligomers (so-called raw MDI). Examples of suitable cycloaliphatic polyisocyanates are the hydrogenation products of the aforementioned aromatic diisocyanates such as, for example, 4,4'-dicyclohexylmethane diisocyanate (H ₁₂ MDI), 1-isocyanatomethyl-3-isocyanato-1, 5,5-trimethyl-cyclohexane (isophorone diisocyanate, IPDI), Cyclohexane-1,4-diisocyanate, hydrogenated xylylene diisocyanate (H XDI), m- or p-tetramethylxylene diisocyanate (m-TMXDI, p-

TMXDI) and dimer fatty acid diisocyanate. Examples of aliphatic polyisocyanates are hexane-1,6-diisocyanate (HDI), 1,6-diisocyanato-2,2,4-trimethylhexane, 1,6-diisocyanato-2,4,4-trimethylhexane, butane-1, 4-diisocyanate and 1, 12-dodecane diisocyanate (C DI).

Suitable di- and / or polyols are preferably the liquid polyhydroxy compounds having two or three hydroxyl groups per molecule, such as, for example, di- and / or trifunctional polypropylene glycols in the molecular weight range from 200 to 6000, preferably in the range from 400 to 3000 statistical and / or block copolymers of ethylene oxide and propylene oxide can also be used. Another group of polyethers that are preferably used are the polytetramethylene glycols, which are produced, for example, by the acidic polymerization of tetrahydrofuran the molecular weight range of the polytetramethylene glycols is between 200 and 6000, preferably in the range from 400 to 4000.

Also suitable as polyols are the liquid polyesters which are obtained by condensation of di- or tricarboxylic acids, e.g. Adipic acid, sebacic acid, glutaric acid, azelaic acid, hexahydrophthalic acid or phthalic acid with low molecular weight diols or triols such as e.g. Ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, 1, 4-butanediol, 1, 6-hexanediol, 1, 10-decanediol, glycerol or trimethylolpropane can be produced.

Another group of the polyols to be used according to the invention are the polyesters based on ε-caprolactone, also called "polycaprolactones".

However, polyester polyols of oleochemical origin can also be used. Such polyester polyols can, for example, by completely ring opening epoxidized triglycerides of an at least partially olefinically unsaturated fatty acid-containing fat mixture with one or more alcohols with 1 to 12 C atoms and then partial transesterification of the triglyceride derivatives to alkyl ester polyols with 1 to 12 C atoms in the alkyl radical are produced (see for example DE-A-3626223). Other suitable polyols are polycarbonate polyols and dimer diols (from Henkel) and castor oil and its derivatives. The hydroxyl-functional polybutadienes, such as those e.g. are available under the trade name "Poly-bd" can be used as polyols for the compositions according to the invention.

Furthermore, the low molecular weight hydroxy-functional (meth) acrylate polymers disclosed in EP-A-205846 can be used as polyols. The known condensation products of phenol and / or resorzine with formaldehyde can be used as novolak resins or phenolic resins. The co-condensates with terpenes, ie the terpene phenol resins, can also be used here.

The adhesive compositions according to the invention basically contain at least one structural component of the general formula I containing di- or polysulfide bonds and one structural component of the general formula II. The two components must of course be matched to one another. Examples of useful combinations are:

A suitable combination of the structural components according to formula I and formula II can, however, also be in binders based on liquid rubbers which are polymerized with vulcanization systems containing sulfur and / or sulfur compounds. Specific examples of the liquid rubbers used for this are given on page 5 in WO 96/36660. Suitable sulfur-containing vulcanizing agents for this purpose are disclosed on page 6 last paragraph to page 7 first paragraph of WO 96/36660. The adhesive compositions according to the invention can additionally contain plasticizers. Basically, all common plasticizers can be used here, examples include the C ₆ -C ₁₄ dialkyl esters of phthalic acid, alkyl benzyl esters of phthalic acid, benzoates of di- or trifunctional polyols such as dipropylene glycol dibenzoate, alkyl sulfonic acid esters of phenol and cresol, aryl phosphates , Alkyl phosphates, C ₆ -C ₁₄ diesters of aliphatic C ₄ -C ₁₀ dicarboxylic acids and / or polymer plasticizers based on diols and dicarboxylic acids and mixtures thereof.

The adhesive compositions can furthermore contain fillers in amounts of between 5 and 60% by weight. Examples of suitable fillers are limestone flour, natural, ground chalk (calcium carbonate or calcium magnesium carbonate), precipitated chalk, difficult to save, talc, mica, clays, soot and color pigments such as e.g. Titanium dioxide or iron oxides.

Furthermore, the adhesives according to the invention can contain further auxiliaries and additives, such as e.g. Anti-aging agents and stabilizers, rheology aids such as fumed silicas, bentones, castor oil derivatives, as well as catalysts and accelerators and, if necessary, tackifying resins.

To release the adhesive bond according to the present invention, the adhesive compositions contain inert cleaving agents under normal use. These cleavage agents have the task of cleaving the di- or polysulfide bonds built into the polymer system again. These cleavage agents are either mercapto compounds optionally with the addition of inorganic or organic basic compounds or other accelerators or they are reducing agents for reductive cleavage of the SS bonds of the adhesive. If necessary, the cleaving agents can also cause a catalytic or thermal cleavage of the SS bonds of the adhesive. If necessary, the cleavage agents can also contain further auxiliaries, in particular swelling agents, the latter facilitating and accelerating the attack of the cleavage agents by swelling of the crosslinked polymer matrix of the adhesive system.

Specific examples of the mercapto compounds to be used according to the invention as cleavage reagent are 2-mercaptobenzoic acid (thiosalicylic acid), 2-mercaptobenzothiazole (2-benzothiazolethiol), 2-mercapto-benzoxazole (2-benzoxazolethiol), DL-mercapto-succinic acid (thioaepfelic acid) , 2-mercapto-4 (3H) - quinazoline, 2-mercaptoquinoline (2-quinolinethiol), 2-mercapto-1-methylimizazole, 5-mercapto-1-methyl-1 H-tetrazole, 2-mercapto-5- methyl-1, 3,4-thia-diazole, 3-mercapto-4-methyl-4H-1, 2,4-triazole, 4-mercaptophenol, 5-mercapto-3-phenyl-1, 2,4- oxadiazole, 5-mercapto-1-phenyl-1 H-tetrazole, N- (2-mercaptopropionyl) glycine, 2-mercapto-2-thiazoline, triphenylmethylmer-captane, 4-toluenethiol, 2-mercaptopyrimidine, 3-mercapto-1 , 2,4-triazole, 2-mercapto-4-methypyrimidine hydrochloride, 2-mercaptobenzimidazole. Specific examples of the reducing agents are trialkyl or triarylphosphines which are solid at room temperature.

There are various ways to make the cleavage reagents so inert at room temperature that they allow a bond that creates a stable bond at all temperatures and is only activated when necessary. One possibility is the choice of crystalline fission Reagents of the aforementioned type which have a sufficiently high melting point so that they are dispersed in the adhesive matrix in largely inert form at normal use temperatures. A further possibility is the encapsulation of the cleavage reagents, this can be done in two ways, on the one hand the cleavage reagent can be encased with a separate inert capsule material, and on the other hand an encapsulation of the cleavage reagent particles can take place by an in-situ surface reaction. Another possibility is the use of chemically blocked cleavage reagents and the use of topologically or sterically inactivated cleavage reagents or the use of kinetically inhibited cleavage reagents.

The activation of the inert cleavage reagents in the adhesive matrix can be achieved by melting, changing the conformation, accelerating the reaction (especially in the case of catalysts), triggering chemical reactions by splitting off protective groups or by in-situ generation of active centers or by capsule detonations (explosion of the inert outer layers of the microencapsulation or by Bursting of the capsule core) or by activation of cleavage catalysts which are inert at the use temperature.

A number of methods can be used to activate the inert cleavage reagents or inert catalysts. On the one hand, the bonded area can be heated, on the other hand by activating heat radiation (IR radiation), by acting on particle radiation, by passing electrical current (in the case of electrically conductive adhesive formulations) and by acting on electrical and in particular electromagnetic fields Cleavage reagents are caused. When selecting electromagnetic see or magnetic fields, a large number of so-called IMS frequencies are available (industrial, medical, science applications). Electromagnetic radiation means the approved IMS frequencies in the radio frequency range up to about 100 MHz as well as the microwaves, which are usually in the range between 0.9 and 10 GHz. Another method for activating the inert cleavage reagents or inert catalysts is the use of ultrasound energy or the use of energetic pressure or shock waves.

Another embodiment of the releasable adhesive connections according to the invention is that normal adhesives according to the prior art are used for the joining and that a cleavable primer is used. As is known, many adhesive bonds still require primers to be applied to at least one of the substrates to be joined. In the sense of this invention, the primer can contain a structural component according to general formula I. In this way, the primer layer can be cleaved with the cleavage agents according to the invention using the same principle of action as described above, so that the joined parts are detached in the sense of this invention without the adhesive as such being subjected to the cleavage reaction.

The invention is to be explained in more detail with reference to the following exemplary embodiments, the selection of the examples not being a limitation of the scope of the subject matter of the invention. Unless otherwise stated, all amounts in the examples below are percentages by weight based on the total composition or parts by weight. Examples

Steel sheets according to DIN 1541 / ST 1206 with the dimensions 1.5 mm x 25 mm x 100 mm (sandblasted or sanded, degreased with dichloromethane) were used for the bonding and detacking tests. A two-component insulating glass adhesive based on a polysulfide polymer, Terostat 998 R from Henkel Teroson, was used as the adhesive. Varying amounts of a fine powdered cleavage reagent were dispersed into this adhesive before application.

The adhesive was applied to the steel sheets so that an adhesive joint of 20 x 25 x 0.5 mm was created between the overlapping steel sheets. After curing according to the manufacturer's instructions and storage for 7 days at room temperature, the detackification properties were tested. For this purpose, the glued sheets were clamped on one side in a tripod in an oven and each was loaded with 1.3 kg weight. The temperature and the time at which the bonded test specimen fell apart were determined. Thereby, heating was carried out between room temperature and 50 ° C. at a heating rate of 2.5 ° C./min; between 50 ° C. and 200 ° C., the heating rate was 0.5 ° C./min.

Comparative Example 1 and Examples 1 to 4:

Cleavage reagent used: 2-mercapto-2-thiazoline, the test results are summarized in Table 1: Table 1

The comparative example without cleavage reagent in the adhesive shows that the test specimens are still intact even at temperatures above 200 ° C. after more than 5 days, i.e. H. there was no splitting of the adhesive bond. As can be clearly seen from Examples 1 to 4, the amount of the dispersing agent dispersed can be used to control both the cleavage temperature and the time required to cleave the bond. Both fall significantly with increasing amounts of cleavage.

To demonstrate that a certain minimum temperature must be maintained as the "trigger temperature" to split the bond, the following tests were used:

Adhesions with 1% splitting reagent were stored at a constant temperature of 80 ° C under a load of 1.3 kg, even after 10 days of continuous load no breakage of the bond was observed. Even with bonds that contained 2.5% of split agent, the bond was still intact after 5 days.

In order to determine the "trigger temperature", the test specimens, which had been exposed to 80 ° C for 10 days without breaking the adhesive, were further stored at 100 ° C and 120 ° C under load. No breakage occurred here either the gluing. The same test specimens were then stored at 145 ° C. under load, and the bond broke after 2.5 hours. That is, a bonded test specimen where the adhesive contained 1 wt.% of this Spaltreagenzes, had at a load of 1, 3 kg 2 ^Λ A Std. are heated to 145 ° C to the adhesive matrix to split so that the bond broke.

In the same way as in Examples 1 to 4, 2-mercaptobenzoxazole was dispersed as the cleavage reagent into the adhesive formulation as the cleavage reagent.

The test results are summarized in Table 2:

Table 2

It is also clear here that the trigger temperature for the splitting of the bond depends on the proportion of the splitting agent in the adhesive formulation.

In the following examples, varying amounts of an inert crystalline substance (sodium chloride) were dispersed into the 998 R adhesive terostat and it was observed whether the addition of this filler affects the thermal stability of the bond. The results are summarized in Table 3: Table 3

From this it is clear that the adhesive is stable up to about 250 ° C. without the dispersion of foreign substances. The dispersion of increasing amounts of an inert crystalline substance reduces this temperature resistance slightly to about 170 to 175 ° C. This clearly shows that the admixture of the solid splitting agents according to the invention in Examples 1 to 7 brings about a reduction in the splitting temperature for the adhesive bond by triggering a chemical splitting of the adhesive bond. Both the splitting temperature and the time required can be adjusted within wide limits to the respective requirements .

Claims

Patent claims

1.) Adhesive composition based on at least one binder containing di- or polysulfide bonds for the production of adhesive bonds, characterized in that the adhesive bond can be separated again with a cleaving reagent, the cleaving reagent in the adhesive composition in crystalline, in encapsulated, chemically blocked, in topologically or sterically inactivated or in kinetically inhibited, finely dispersed form.

2.) Adhesive composition according to claim 1, characterized in that the structural components of the binder are selected from the group of epoxy resin combined with di- or polysulfide bonds containing di- or polymercaptans, di- or polythioalkanols, di- or polythiodicarboxylic acids or di- or polythiodi- or polyamines or their mixtures, polyurethane systems composed of monomers or prepolymers di- or poly-isocyanates with di- or polythiodi- or polyamines, di- or polythio-di- and / or polyols, liquid Polyenes (liquid rubber) with vulcanization systems containing sulfur and / or sulfur compounds.

3.) Adhesive composition according to one of the preceding claims, characterized in that the cleavage reagent is selected from one of the following compounds:

2-mercaptobenzoic acid (thiosalicylic acid), 2-mercaptobenzothiazole (2-benzothiazole thiol), 2-mercaptobenzoxazole (2-benzoxazole thiol), DL- Mercapto-succinic acid (thio-malic acid), mercapto-pyruvic acid sodium salt, 2-mercapto-4 (3H) -quinazoline, 2-mercaptoquinoline (2-quinolinethiol), 2-mercapto-1-methylimidazole, 5-mercapto-1-methyl-1 H-tetrazole , 2-mercapto-5-methyl-1, 3,4-thiadiazole, 3-mercapto-4-methyl-4H-1, 2,4-triazole, 4-mercaptophenol, 5-mercapto-3-phenyl-1 , 2,4-oxadiazole, 5-mercapto-1-phenyl-1 H-tetrazole, N- (2-mercaptopropionyl) glycine, 2-mercapto-2-thiazoline, triphenylmethyl mercaptan, 4-toluenethiol, 2-mercaptopyrimidine, 3- Mercapto-1, 2,4-triazole, 2-Mercapto-4-methypyrimidine hydrochloride, 2-Mercaptobenzimidazole.

4. Process for producing and releasing adhesive bonds characterized by the following essential process steps

a) joining and connecting the parts with the aid of an adhesive composition according to claims 1 to 3, the adhesive composition possibly being mixed before application from two or more components b) curing of the adhesive at room temperature or by heating,

c) Loosening the adhesive connection by activating the cleavage reagent dispersed in the adhesive matrix and inert at the temperature of use of the glued parts

d) optionally followed by mechanical stress.

5. The method according to claim 4, characterized in that the inert cleavage reagent by melting, conformational change, split-off blocking protective groups, generation of active centers, detonation of encapsulations or catalytic action.

6. The method according to claim 4 or 5, characterized in that the activation is effected by heating (heat conduction), heat radiation, particle radiation, conduction of electrical current, electrical or electromagnetic fields, ultrasound, pressure or shock waves.