Adhesive formulations containing silanes and hydrophobized fumed silica

Abstract

The present invention relates to a liquid adhesive formulation comprising a base polymer, an alkylsilane and a hydrophobized fumed silica having a low carbon content, i.e. in the range of 0.4-3.5% by weight. The specific combination of alkylsilane and hydrophobized fumed silica significantly increases the viscosity of the adhesive formulation. The present invention further relates to a method for producing such an adhesive formulation and to the use of alkylsilane in combination with hydrophobized fumed silica having a carbon content in the range of 0.4-3.5% by weight to modify the rheological properties of the liquid adhesive formulation.

Description

[Technical field]

[0001] The present invention relates to a liquid adhesive formulation comprising a base polymer, an alkylsilane and a hydrophobized fumed silica having a low carbon content, i.e. in the range of 0.4-3.5% by weight. The specific combination of alkylsilane and hydrophobized fumed silica significantly increases the viscosity of the adhesive formulation. The present invention further relates to a method for producing such an adhesive formulation and to the use of alkylsilane in combination with hydrophobized fumed silica having a carbon content in the range of 0.4-3.5% by weight to modify the rheological properties of the liquid adhesive formulation. [Background technology]

[0002] Adhesive formulations are used in a wide range of industrial sectors for numerous applications. In most cases, such formulations are applied in liquid form or liquefied at some point during application. To improve handling, the rheological properties of liquid adhesive formulations must therefore be tailored to the specific application method. To achieve this, rheological modifiers are added to such formulations. For this purpose, different grades of silica are usually used. In particular, hydrophobized silica grades are used, i.e. silica that has been reacted or treated with more hydrophobic compounds to make the silica surface more hydrophobic. Summary of the Invention [Problem to be solved by the invention]

[0003] Previous methods of adjusting the rheological properties of liquid adhesive formulations by adding silica required the use of hydrophobized silica with a high carbon content. In contrast, the use of hydrophobized silica with a low carbon content only resulted in a small increase in viscosity at low shear rates. Unfortunately, however, hydrophobized silica with a high carbon content is relatively expensive and available in fairly limited quantities. Thus, there is a need in the art for adhesive formulations that facilitate a significant increase in viscosity by adding hydrophobized silica with a low carbon content. The present invention provides such a formulation. [Means for solving the problem]

[0004] The present invention relates to at least one base polymer, at least one hydrophobized fumed silica, and at least one alkylsilane A liquid adhesive composition comprising: the base polymer is selected from epoxy resins, unsaturated polyester resins, polyurethanes, vinyl ester resins, acrylates, polyvinyl acetates, polyvinyl alcohols, polyvinyl ethers, ethylene-vinyl acetate, ethylene-acrylic acid copolymers, polyvinyl acetate, polystyrene, polyvinyl chloride, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, butyl rubber, polysulfides, polyethylene, polypropylene, fluorinated hydrocarbons, polyamides, saturated polyesters and copolyesters, phenol-formaldehyde resins, cresol- / resorcinol-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins, polyimides, polybenzimidazoles, polysulfones, or mixtures thereof; The hydrophobized fumed silica has a carbon content in the range of 0.4 to 3.5% by weight, Alkylsilanes are - Formula I:

[0005] [ka]

[0006] (In the formula, R a = a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms, x=0~2, R=H3C-(CH2) y (y=0~2). or -Formula II:

[0007] [ka]

[0008] (wherein R=a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms; R1=H3C-(CH2) y (y=0~2), X=H3C- or H3C-(CH2) y O-(y=0~2), n=0~20.) or -Formula III:

[0009] [ka]

[0010] (wherein R=a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms; R1=H3C-(CH2) y (y=0~2), X=H3C- or H3C-(CH2) y O-(y=0~2), n=0~20, m=0~20.) or -Formula IV:

[0011] [ka]

[0012] (wherein R=a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms; R1=H3C-(CH2) y (y=0~2), X=H3C- or H3C-(CH2) y O-(y=0~2), n=0~20.) or mixtures of monomeric alkylsilanes of formula I with linear, branched and / or cyclic oligomeric alkylsilanes of formula II, formula III and / or formula IV, The present invention relates to a liquid adhesive composition selected from the group consisting of:

[0013] In the context of this specification, an adhesive, adhesive composition, or adhesive formulation (all three terms are used interchangeably) is defined as a non-metallic material capable of joining adherends with surface adhesion and internal strength. The prior art lists a large number of different adhesives, the majority of which are based on organic compounds.

[0014] A distinction is made between physically curing and chemically curing adhesives. Physically curing adhesives are those in which the final adhesive substance (often a polymer) is used as is and the adhesive subsequently solidifies by physical methods. Thus, for example, hot melt adhesives, dispersion adhesives, wet adhesives with organic solvents and contact adhesives are known. A common feature of all these types of adhesives is that the adhesive is first applied in a processable form and then solidification occurs, for example as a result of evaporation of the solvent or cooling. In the case of chemically curing adhesives, the individual components are applied and then a new product is formed via solidification by chemical reaction of the individual components. Reactive adhesives are two-component and one-component systems. In the case of two-component systems, the adhesive is applied from separate components and solidifies by chemical reaction. In the case of one-component adhesives, the adhesive hardens by chemical reaction as a result of a change in the ambient conditions, for example temperature increase, air inflow, evaporation, moisture or atmospheric oxygen. The group of chemically cured adhesives includes, for example, cyanoacrylate adhesives, methyl methacrylate adhesives, anaerobic curing adhesives, radiation curing adhesives, phenol-formaldehyde resin adhesives, silicones, silane cross-linked polymer adhesives, polyimide adhesives, epoxy resin adhesives, and polyurethane adhesives. A general overview of the various adhesives can be found in Ullman's Encyclopedia of Industrial Chemistry, 4th Edition, Vol. 14, p. 227 et seq. (1997).

[0015] In the context of this specification, liquid adhesive formulations are considered to be adhesive formulations that are applied in liquid form or liquefy at some point during application. In the context of this specification, adhesives are products that, depending on their respective chemical composition and physical state when applied to the adherend, allow surface wetting and form the adhesive layer necessary for the transmission of forces between the adherends in the adhesive joint. Compared to sealants, adhesives have higher tensile shear strength and lower elongation values. In other words, adhesives are rigid to elastic, and sealants are elastic to plastic. Like sealants, adhesives contain similar components such as solvents (e.g. ketones), water, fillers (e.g. chalk), thixotropic agents (e.g. pyrogenic silica), adhesion promoters (e.g. silanes), color pastes (e.g. pigment grade carbon black), and further additives (e.g. catalysts, anti-aging agents) in addition to the base polymers that are well known to those skilled in the art.

[0016] In particular, fumed silica is known to act as a very effective thixotropic agent (see, for example, Winnacker-Kuchler, Chemische Technologie, Vol. 3 (1983), 4th edition, p. 77, and Ullmann's Encyclopedia of Industrial Chemistry, Vol. 21, p. 462 ff., 4th edition (1982)). Fumed silica is widely used, for example, in adhesives based on epoxy resins (Degussa Pigments Brochure Series (2001) Nos. 27 and 54). The application of fumed silica as a rheology modifier in adhesive formulations may be facilitated when the silica is difficult to handle by using hydrophobized fumed silica, i.e., fumed silica that has been reacted or treated with an organic compound (usually an organosilicon compound such as dimethyldichlorosilane, trimethoxyoctylsilane, polydimethylsiloxane, or hexamethyldisilazane) to replace at least a portion of the silanol groups on the fumed silica surface with less hydrophilic groups.

[0017] In the context of this specification, hydrophobized fumed silica is defined as fumed silica that has been reacted or treated with an organic compound (usually an organosilicon compound such as dimethyldichlorosilane, trimethoxyoctylsilane, polydimethylsiloxane, hexamethyldisilazane, or octamethylcyclotetrasiloxane) to replace at least a portion of the silanol groups on the surface of the fumed silica with less hydrophilic groups. Combinations of fumed silica can also be used to prepare the adhesive composition. Methods for preparing hydrophobic fumed silica are well known in the art, and include, for example, the methods described in US Patent Publication No. 2010200803.

[0018] The hydrophobicity of a particular charge hydrophobized fumed silica can be assessed from its carbon content: a higher carbon content means a higher hydrophobicity, and a lower carbon content means a lower hydrophobicity.

[0019] In the present context, the carbon content of the hydrophobized fumed silica is understood to be the carbon content measured according to DIN EN ISO 3262-20, which is carried out as follows: a sample is burned in an induction furnace in a flow of oxygen, optionally in a crucible coated with a suitable catalyst. Sulfur compounds, halogens and water vapor are removed from the combustion products, which are then passed over a platinum catalyst (to convert carbon monoxide to carbon dioxide) and the carbon dioxide concentration is measured with an infrared cell detector.

[0020] The hydrophobized fumed silica of the liquid adhesive composition of the present invention exhibits a carbon content in the range of 0.4 to 3.5% by weight.

[0021] In a preferred embodiment, the at least one hydrophobized fumed silica in the liquid adhesive composition according to the invention exhibits a carbon content in the range of 0.4 to 3.0% by weight.

[0022] In a particularly preferred embodiment, the at least one hydrophobized fumed silica in the liquid adhesive composition according to the invention exhibits a carbon content in the range of 0.4 to 2.0% by weight.

[0023] In another particularly preferred embodiment, the at least one hydrophobized fumed silica in the liquid adhesive composition according to the invention exhibits a carbon content in the range of 1.0 to 3.0% by weight.

[0024] In another particularly preferred embodiment, the at least one hydrophobized fumed silica in the liquid adhesive composition according to the invention is selected from AEROSIL® R974 (carbon content = 0.9-1.5 wt.%), AEROSIL® R106 (carbon content = 1.4-3.0 wt.%), or mixtures thereof.

[0025] The hydrophobized fumed silica is usually added to the adhesive composition in a mass fraction of 1 to 30% by weight of the total mass of the respective composition. Thus, in a preferred embodiment of the present invention, the total mass of at least one hydrophobized fumed silica according to the present invention is in the range of 1 to 30% by weight of the total mass of the liquid adhesive composition. In a particularly preferred embodiment of the present invention, the total mass of at least one hydrophobized fumed silica according to the present invention is in the range of 2 to 10% by weight of the total mass of the liquid adhesive composition.

[0026] Many base polymers suitable for the adhesive formulations of the present invention are well known to those skilled in the art.

[0027] The adhesive composition of the present invention comprises as a base polymer any of epoxy resins, unsaturated polyester resins, polyurethanes, vinyl ester resins, acrylates, polyvinyl acetates, polyvinyl alcohols, polyvinyl ethers, ethylene-vinyl acetate, ethylene-acrylic acid copolymers, polyvinyl acetate, polystyrene, polyvinyl chloride, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, butyl rubber, polysulfides, polyethylene, polypropylene, fluorinated hydrocarbons, polyamides, saturated polyesters and copolyesters, phenol-formaldehyde resins, cresol- / resorcinol-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins, polyimides, polybenzimidazoles, polysulfones, or mixtures thereof.

[0028] In a particularly preferred embodiment of the present invention, the base polymer is an epoxy resin.

[0029] In the most preferred embodiment of the present invention, the base polymer is Epikote TM It is Resin828.

[0030] Epoxy resins are preferably used as base polymers for adhesives. They are prepared, for example, by condensing 2,2-bis(4-hydroxyphenyl)propane with epichlorohydrin in a basic medium. Depending on the equivalents of both reactants used, the products are glycidyl ethers of different molar masses. In recent years, epoxy resins from bisphenol F, novolac epoxy resins, and cycloaliphatic and heterocyclic epoxy resins have also gained importance.

[0031] Epoxy resins have poor film-forming ability by themselves, so molecular expansion with a suitable crosslinker is necessary. Examples of crosslinkers used for epoxy resins include polyamines, polyaminoamides, carboxylic anhydrides, and dicyandiamide. Amine hardeners include aliphatic, cycloaliphatic, aromatic, and araliphatic polyamines. Curing is carried out without removing the reaction products. In general, reactive hydrogen atoms are added to the epoxy groups to form hydroxyl groups.

[0032] Unsaturated polyester resins are preferably used as base polymers for adhesives. They are obtained by polycondensation of unsaturated and saturated di- or polycarboxylic acids with alcohols. Under suitable reaction conditions, double bonds remain in the acids and / or alcohols, allowing polymerization reactions with unsaturated monomers such as styrene. The unsaturated dicarboxylic acids preferably used are maleic anhydride, maleic acid and fumaric acid.

[0033] Preferably used saturated dicarboxylic acids are orthophthalic acid and orthophthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, adipic acid, azelaic acid, sebacic acid, hexachloroendomethylenetetrahydrophthalic acid, tetrabromophthalic acid.

[0034] Glycols which are preferably used are propylene 1,2-glycol, ethylene glycol, butylene glycol, neopentyl glycol, 2,2,4-trimethylpentane-1,3-diol, dibromoneopentyl glycol, diethylene glycol, triethylene glycol, dipropylene glycol, pentaerythritol diallyl ether, dicyclopentadiene.

[0035] Crosslinking monomers which are preferably used are styrene, α-methylstyrene, meta- and para-methylstyrene, methyl methacrylate, diallyl phthalate, triallyl cyanurate.

[0036] This list is not exhaustive of the number of possible starting materials. Those skilled in the art can use other compounds depending on the raw material situation. In addition, the addition of dicyclopentadiene is customary, which results in a change in the reactivity of the resin. The "unsaturated polyester resin" produced can be used as is or diluted with reactive monomers. The reactive monomers are styrene, stilbene, acrylic esters, methacrylic esters, diallyl phthalate, and other unsaturated compounds, provided that they have a sufficiently low viscosity and sufficient miscibility with the unsaturated polyester resin.

[0037] Polyurethane resins are preferably used as base polymers for adhesives. Polyurethanes are derived from isocyanic acid. Being highly reactive compounds, they undergo addition reactions very easily with compounds that have active hydrogen atoms. In the course of this reaction, the nitrogen-carbon double bond is broken, and the active hydrogen is attached to the nitrogen and the oxygen-bonding group to the carbon, forming a urethane group. To obtain the higher molecular weight crosslinked polyurethanes of the type required for adhesive and sealant layers, it is necessary to prepare reaction partners that are starting products with at least two functional groups, such as diisocyanates or triisocyanates, for example diphenylmethane 4,4-diisocyanate (MDI) with polymeric fractions, or tolylene diisocyanate (TDI), and polyols, with polyhydric alcohols (diols or polyols, compounds with two or more hydroxyl functional groups in the molecule). This type of alcohol can be present, for example, in the form of saturated polyesters prepared with an excess of polyalcohols.

[0038] Two-component reactive adhesives consist of low molecular weight polyisocyanates and also relatively low molecular weight polyols, such as polyether polyols or polyester polyols, such as polyalkylene polyadipates. After mixing the two components, urethane groups are formed in the adhesive or adhesive layer.

[0039] One-component reactive adhesives consist of relatively high molecular weight polyurethanes, which cure by reacting with atmospheric moisture. In principle, this situation is also one of two mutually reacting chemical components, but only one physical component is supplied for the adhesive process. Since simple low molecular weight polyisocyanates, when reacted with moisture, form relatively hard and brittle adhesive layers with low strength values, one-component systems start from pre-crosslinked polymers, known as prepolymers. These compounds are prepared from relatively high molecular weight polyols and a stoichiometric excess of isocyanates. Thus, the compounds present already have urethane bonds, but also reactive isocyanate groups that are prone to react with moisture. The reaction with water proceeds with the formation of urea bonds. Primary amines formed in the course of the decomposition reaction instantly react with other isocyanate groups to form polyureas. Thus, in the case of one-component systems, the fully cured polymer contains not only urethane compounds but also urea compounds.

[0040] Solvent-based polyurethane adhesives are available as physically cured and chemically reactive systems. In the physically cured systems, the polymer is in the form of a high molecular weight hydroxyl polyurethane and the solvent used is, for example, methyl ethyl ketone. Chemically reactive systems further include the hydroxyl polyurethane and another polyisocyanate as a crosslinker and second component.

[0041] Dispersion adhesives include high molecular weight polyurethane dispersed in water.

[0042] In the case of heat-activated polyurethane adhesives, the isocyanate component is in a "capped" or "blocked" form in a compound that only removes the isocyanate component at relatively high temperatures.

[0043] Reactive polyurethane hot melt adhesives are prepared using relatively high molecular weight crystallizable and meltable diol and isocyanate components. These components are applied to the substrate as a hot melt adhesive at temperatures of about 70°C to 120°C. After cooling, the bond acquires sufficient initial strength that it can be rapidly further processed. The still present reactive isocyanate groups are then exposed to further moisture, resulting in crosslinking via urea bonds to form the adhesive layer polymer.

[0044] As base polymers for adhesives, vinyl ester resins are preferably used. In terms of chemistry, vinyl ester resins have a certain relationship with UP resins, especially with regard to the curing reaction, processing technology and field of use. These resins are polyadducts of liquid epoxy resins and acrylic acid. As a result of the reduction of ester groups in the molecular chain, these resins have better hydrolysis resistance, together with effective elasticity and impact toughness. The monomers used for crosslinking are the same as for unsaturated polyester resins, in particular styrene.

[0045] As base polymers for the adhesives preferably acrylates are used. The general term "acrylate adhesives" includes all reactive adhesives which cure via the carbon-carbon double bonds of the acrylic groups.

[0046] In adhesive formulations, methacrylic acid esters and α-cyanoacrylic acid esters are of particular importance. The curing of acrylate adhesives is carried out by addition polymerization, during which an initiator sets up a chain reaction leading to the continuous hardening of the adhesive. The polymerization of "acrylate" adhesives is initiated by free radicals or, in the case of α-cyanoacrylic acids, by anions. Depending on the polymerization mechanism utilized for curing, acrylate adhesives are also subdivided into the following groups:

[0047] Anionically curing adhesive: α-cyanoacrylic acid one-component adhesive, Free radical curing adhesive: anaerobic one-component adhesive, Free radical curing adhesive: two-component adhesive

[0048] For sealants based on polyacrylates or acrylate copolymers and polymethacrylates a distinction is made between solvent-based and water-based systems: Polyacrylate sealants harden physically by evaporation of the solvent or dispersing water.

[0049] Polyvinyl acetate is preferably used as the base polymer for adhesives. It is the polymerization product of vinyl acetate. Due to the highly polar acetate groups present in the molecule, polyvinyl acetate has very good adhesive properties to many substrate surfaces. It is mainly used as a dispersion adhesive with a solid content of about 50% to 60%, and sometimes it is based on vinyl acetate copolymers (such as vinyl chloride).

[0050] Polyvinyl alcohol is preferably used as the base polymer for the adhesive.

[0051] Polyvinyl alcohol is produced as a hydrolysis product of polyvinyl acetate and other similar polyesters. Depending on the molecular weight, polyvinyl alcohol is in the form of a more or less viscous liquid. It is used, for example, in bonding cellulosic materials such as paper, cardboard, and wood, and also as a protective colloid to stabilize dispersion adhesives and speed up their setting.

[0052] Polyvinyl ethers are preferably used as base polymers for adhesives. Among the polyvinyl ethers, three polymers in particular are of interest as base materials for adhesives: polyvinyl methyl ether, polyvinyl ethyl ether, polyvinyl isobutyl ether.

[0053] Polyvinyl ethers of moderate polymerization degree are tacky plastic resins with very good adhesion to porous and smooth surfaces. Polyvinyl methyl ethers are particularly noteworthy in that, due to their water solubility, they can be rewetted, thus improving their adhesive properties when mixed with dextrins or glues, for example, and used as gums for labels. Polyvinyl ethers are also used in pressure-sensitive adhesives due to their permanent tack.

[0054] Ethylene vinyl acetate is a copolymer of ethylene and vinyl acetate, preferably used as a base polymer for adhesives. In its molecular structure, vinyl acetate molecules are randomly integrated into the ethylene chain. Removal of acetic acid makes polyvinyl acetate relatively unstable to temperature loads, while its copolymers with ethylene are significantly more resistant to oxidation and thermal degradation. For this reason, EVA copolymers with a vinyl acetate fraction of about 40% are included in an important group of base materials for hot melt adhesives.

[0055] Ethylene-acrylic acid copolymers are preferably used as base polymers for adhesives. They are copolymers of ethylene with acrylic acid and / or acrylic acid esters.

[0056] These copolymers, which combine the chemical resistance of polyethylene with the excellent properties of the acid and / or ester moieties, are important base polymers for hot melt adhesives. The ester component used is preferably ethyl acrylate.

[0057] Polyvinyl acetals are preferably used as base polymers for adhesives. They are produced by the reaction of aldehydes with alcohols. The most important acetals for the production of adhesives are polyvinyl formal and polyvinyl butyral. Both act as plasticizing components in phenolic resin adhesives. Furthermore, polyvinyl butyral finds application as an adhesive film in laminated safety glass.

[0058] Polystyrene is preferably used as the base polymer for adhesives. This monomer is used as a component of the base material for adhesives in two main areas: As a copolymer with plasticizing monomers, especially butadiene, for the preparation of styrene-butadiene dispersions, and as a "polymerizable" solvent for copolymerization with unsaturated polyesters.

[0059] Polyvinyl chloride is preferably used as a base polymer for adhesives, more specifically in plastisol adhesives, as a copolymer with vinyl acetate to give vinyl chloride / vinyl acetate copolymers in solvent-based adhesives, dispersion-based adhesives, heat seal adhesives, and as a high-frequency welding aid.

[0060] Styrene butadiene rubber is preferably used as the base polymer for adhesives. Styrene butadiene rubber is a typical example of a thermoplastic elastomer, combining the application properties of elastomers with those of thermoplastics. Styrene butadiene copolymers (SBS) and styrene isoprene copolymers (SIS) are so-called triblock copolymers, which are linearly composed of consecutive identical monomer units in the individual blocks. The end blocks are polystyrene segments and the midblock is polybutadiene (styrene butadiene styrene block copolymer, SBS) or isoprene (styrene isoprene styrene block copolymer, SIS).

[0061] The ratio of the styrene fraction to the butadiene fraction or the styrene fraction to the isoprene fraction is about 1:3. In this method, an "internal plasticization" is achieved, unlike adhesive layer polymers that have elastic properties due to the addition of plasticizers. A particular advantage of these rubber copolymers is the ability to form adhesive layers with good adhesive properties and high flexibility. They therefore find important applications in situations where the adhesively bonded adherends are subject to high deformation stresses in practical use, such as footwear with rubber / rubber or rubber / metal bonds.

[0062] Chloroprene rubber (CR) is preferably used as the base polymer for adhesives. Chloroprene rubber (polychloroprene) is produced as a polymerization and copolymerization product of chloroprene (2-chlorobutadiene). In addition to good adhesive properties, the linear macromolecules have a strong tendency to crystallization, which results in a relatively high strength of the adhesive layer. These polymers and copolymers are important base materials for contact adhesives. The double bonds present in the polychloroprene molecules allow further crosslinking with corresponding reactive molecular groups. Thermosetting components used for this purpose include isocyanates and phenolic resins.

[0063] Nitrile rubber (NBR) is preferably used as the base polymer for adhesives. Nitrile rubber is a copolymer of butadiene and about 20% to 40% acrylonitrile. Due to the high proportion of acrylonitrile, these polymers have an effective plasticizer resistance and are very suitable, for example, for bonding plasticized plastics.

[0064] Butyl rubber is preferably used as the base polymer for adhesives. It is a copolymer based on isobutylene and isoprene. Within this linear molecule there is a very large chain fraction of saturated character, in the form of long polyisobutylene segments, which makes further crosslinking impossible. The only crosslinkable component is the isoprene molecule, so the overall properties of the butyl rubber depend on the proportion of the number of double bonds predetermined by the isoprene. The reactivity can be further influenced by the incorporation of monomers containing chlorine or bromine.

[0065] Polysulfides are preferably used as base polymers for adhesives. The raw material for polysulfide sealants has long been known under the trade name Thiokol®. Polysulfide polymers are obtained by reaction of dichloroethyl formal with sodium polysulfide. The molecular weight of the liquid polymers is 3000-4000. They can be converted to the ultimate rubber-elastic state by reaction with an oxidizing agent, for example manganese dioxide.

[0066] Polyethylene is preferably used as the base polymer for adhesives. Low molecular weight types with melt indices in the range of 2-2000 g / 10 min are used as hot melt adhesives in the paper and cardboard industry in combination with tackifying resins and microwaxes.

[0067] Polypropylene is preferably used as the base polymer for adhesives. Polypropylene is used as the base material for hot melt adhesives having medium strength properties, more particularly in the form of atactic polypropylene.

[0068] Fluorinated hydrocarbons are preferably used as the base polymer for adhesives. Polyfluoroethylene propylene is a copolymer of tetrafluoroethylene and hexafluoropropylene and has been studied as a base material for hot melt adhesives. The advantage of these products is their high long-term heat resistance.

[0069] Polyamides are preferably used as base polymers for adhesives. They are some of the most important base materials for physically setting hot melt adhesives. Suitable reactions for the production of polyamides are the following, which are usually carried out in the melt under nitrogen: polycondensation of diamines with dicarboxylic acids, polycondensation of aminocarboxylic acids, polycondensation from lactams, polycondensation of diamines with dimerized fatty acids.

[0070] Saturated polyesters and copolyesters are preferably used as base polymers for adhesives. They are produced by polycondensation of dicarboxylic acids and diols. They are important base materials for hot melt adhesives.

[0071] Phenol-formaldehyde resins are preferably used as base polymers for adhesives. These polymers are produced by polycondensation reaction of phenol with formaldehyde to form highly crosslinked phenolic resins, which are used as base materials for adhesives, for example, for aircraft manufacturing. Pure phenol-formaldehyde resins are generally too brittle. For this reason, they are modified with thermoplastic polymers by copolymerization or co-condensation, for example, with polyvinyl formal, polyvinyl butyral, polyamide, epoxy resins, or elastomers, such as polychloroprene and nitrile rubber.

[0072] Cresol / resorcinol-formaldehyde resins are preferably used as base polymers for adhesives. In addition to phenol as the starting monomer for formaldehyde condensation, phenol derivatives such as cresol and resorcinol are also used as co-reactants.

[0073] Urea-formaldehyde resins are preferably used as base polymers for adhesives. Many nitrogen-containing organic compounds can be polycondensed with aldehydes. For adhesive applications, urea and melamine have become particularly important. In the case of urea-formaldehyde resins, the reaction sequence initially takes place in the form of an addition reaction in a weakly acidic solution. The actual polycondensation reaction leading to the formation of the polymer adhesive layer results in a highly crosslinked polymer via the formation of ether or methylene bridges.

[0074] Melamine-formaldehyde resins are preferably used as the base polymer for adhesives. Like urea, melamine also reacts with formaldehyde to form methylol compounds. As in the urea reaction, polycondensation with these compounds also proceeds via methylene or methylene ether bonds to form high molecular weight, highly crosslinked, hard and sometimes brittle adhesive layers.

[0075] Polyimides are preferably used as base polymers for adhesives. Experiments on the use of polyimides were carried out due to the interest in obtaining organic adhesives that could meet the challenges of high temperatures. The preparation of technically available polyimides is achieved by reaction of tetrabasic acid anhydrides, such as pyromellitic anhydride, with aromatic diamines, such as diaminodiphenyl oxide. The use as adhesives is achieved starting from precondensates in the form of solutions or films.

[0076] Polybenzimidazoles are preferably used as base polymers for adhesives.

[0077] Polybenzimidazoles are also classified as high heat resistant adhesives. They are formed by the polycondensation reaction of aromatic tetraamines with dicarboxylic acids.

[0078] Polysulfones are preferably used as base polymers for adhesives. They also belong to the group of heat-resistant adhesives. They are obtained, for example, by polycondensation reaction of dihydroxydiphenylsulfone with bisphenol A.

[0079] The alkyl silane component of the liquid adhesive composition of the present invention is selected from the following: Alkylsilanes are - Formula I:

[0080] [ka]

[0081] (In the formula, R a = a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms, x=0~2, R=H3C-(CH2) y (y=0~2). or -Formula II:

[0082] [ka]

[0083] (wherein R=a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms; R1=H3C-(CH2) y (y=0~2), X=H3C- or H3C-(CH2) y O-(y=0~2), n=0~20.) or -Formula III:

[0084] [ka]

[0085] (wherein R=a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms; R1=H3C-(CH2) y (y=0~2), X=H3C- or H3C-(CH2) y O-(y=0~2), n=0~20, m=0~20.) or -Formula IV:

[0086] [ka]

[0087] (wherein R=a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms; R1=H3C-(CH2) y (y=0~2), X=H3C- or H3C-(CH2) y O-(y=0~2), n=0~20.) or mixtures of monomeric alkylsilanes of formula I with linear, branched and / or cyclic oligomeric alkylsilanes of formula II, formula III and / or formula IV, is selected from.

[0088] In a preferred embodiment, the at least one alkyl silane in the liquid adhesive composition according to the invention is - Formula I:

[0089] [ka] (I)

[0090] (In the formula, R a = a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms, x=0~2, R=H3C-(CH2) y (y=0~2). or -Formula II:

[0091] [ka]

[0092] (wherein R=a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms; R1=H3C-(CH2) y (y=0~2), X=H3C- or H3C-(CH2) y O-(y=0~2), n=0~20.) or a mixture of monomeric alkylsilanes of formula I and linear oligomeric alkylsilanes of formula II is selected from.

[0093] In another preferred embodiment, the at least one alkylsilane in the liquid adhesive composition according to the invention is selected from propyltrimethoxysilane, propyltriethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, oligomeric alkoxysilanes (e.g. Dynasylan® SIVO502 (oligomeric alkylsilane, ethoxy-based)), or mixtures thereof.

[0094] In another preferred embodiment, the at least one alkylsilane in the liquid adhesive composition according to the present invention is an oligomeric alkoxysilane (e.g., Dynasylan® SIVO502), hexadecyltrimethoxysilane, or a mixture thereof.

[0095] In a particularly preferred embodiment, the at least one alkylsilane in the liquid adhesive composition according to the present invention is hexadecyltrimethoxysilane.

[0096] The rheological effect obtained by combining the hydrophobized fumed silica according to the invention with an alkylsilane can be obtained over a wide range of silica / silane mass ratios. In a preferred embodiment of the invention, the total mass of the at least one alkylsilane according to the invention is in the range of 5 to 60% by weight of the total mass of the hydrophobized fumed silica according to the invention contained in the liquid adhesive composition. In a particularly preferred embodiment of the invention, the total mass of the at least one alkylsilane according to the invention is in the range of 20 to 40% by weight of the total mass of the hydrophobized fumed silica according to the invention contained in the liquid adhesive composition.

[0097] In another aspect, the present invention further relates to a method for the preparation of a liquid adhesive composition comprising at least one base polymer according to the present invention, at least one hydrophobized fumed silica and at least one alkylsilane, comprising the steps of: - mixing at least one base polymer, at least one hydrophobized fumed silica, at least one alkylsilane and, optionally, other components of the liquid adhesive composition according to the invention.

[0098] In another aspect, the present invention further relates to a liquid adhesive composition obtainable by such a method.

[0099] The adhesives of the present invention are typically used in applications such as automotive, construction, windmill adhesive pastes, chemical anchors, insulating glass units, structural wood components, and the like.

[0100] The following examples are intended to explain the invention in more detail. EXAMPLES

[0101] For each composition listed in Tables 1-3, the following procedure was carried out.

[0102] First, the epoxy resin and silane were mixed for 2 minutes using a Speed ​​Mixer DAC 150 FVZ at 2500 upm (94 parts by weight of epoxy resin Epikote® Resin 828 and silane (amount of silane as indicated in Tables 1-3 unless a particular composition does not contain silane).

[0103] Silica (6 or 5 parts by weight, see Tables 1-3) was then added and the resulting composition was first mixed at 3000 upm for 1 minute, after which material scraped from the top of the vessel was added and again mixed at 3000 upm for 2 minutes.

[0104] The resulting mixture was first cooled to 22°C within 90 minutes. The viscosity of the mixture at different shear rates was then measured at 22°C using a rheometer (Physica MCR 301, Physica MCR 302). The samples were then stored at 22°C for the periods ("hours") shown in Tables 1-3, after which the viscosity measurements were repeated.

[0105] As shown by the data in Tables 1 to 3, the addition of oligomeric alkylsilanes increases the viscosity of the compositions at low shear rates. This leads to the conclusion that, even when alkylsilanes are added to the compositions, the thixotropy of such compositions can be very effectively increased by hydrophobized silica. Importantly, this effect can be achieved by hydrophobized silicas with a low carbon content, as was not known in the prior art (the carbon content of AEROSIL® R974 is in the range of 0.9-1.5% by weight, and the carbon content of AEROSIL® R106 is in the range of 1.4-3.0% by weight).

[0106] In particular, the data on the compositions AEROSIL® R974 and AEROSIL® R106 demonstrate this very clearly: the compositions containing AEROSIL® R974 and AEROSIL® R106 without alkylsilanes exhibited a 0.1 second -1 (See Tables 1 and 3) but after the addition of alkylsilane, the viscosity is very low at shear rates of 0.1 s. -1 The viscosity at shear rate increases dramatically.

[0107] High carbon content hydrophobized silicas such as AEROSIL® R202 (the carbon content of AEROSIL® R202 ranges from 3.51 to 5.0 wt%) are often used in adhesive and sealant formulations to achieve thixotropy levels (indicated by high viscosity at low shear rates) and anti-sag properties. However, such high carbon content hydrophobized silicas are relatively expensive and available in limited quantities. It is therefore important to note that the combination of a low carbon content hydrophobized silica such as AEROSIL® R106 with a mixture of alkyl silanes such as Dynasylan® SIVO 502 (oligomeric alkyl silane) results in an epoxy resin composition with a viscosity at low shear rates similar to that of an epoxy resin composition with a high carbon content hydrophobized silica such as AEROSIL® R202 (see Table 1).

[0108] A slight increase in viscosity at low shear rates due to the addition of alkylsilanes can also be observed for high carbon content hydrophobized silicas such as AEROSIL® R202 in epoxy mixtures (see Table 2).

[0109] [Table 1]

[0110] [Table 2]

[0111] [Table 3]

Claims

1. at least one base polymer, at least one hydrophobized fumed silica, and at least one alkylsilane A liquid adhesive composition comprising: the base polymer is selected from epoxy resins, unsaturated polyester resins, polyurethanes, vinyl ester resins, acrylates, polyvinyl acetate, polyvinyl alcohol, polyvinyl ethers, ethylene-vinyl acetate, ethylene-acrylic acid copolymers, polyvinyl acetate, polystyrene, polyvinyl chloride, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, butyl rubber, polysulfides, polyethylene, polypropylene, fluorinated hydrocarbons, polyamides, saturated polyesters and copolyesters, phenol-formaldehyde resins, cresol- / resorcinol-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins, polyimides, polybenzimidazoles, polysulfones, or mixtures thereof; The hydrophobized fumed silica has a carbon content in the range of 0.4 to 3.5 wt. %; The alkylsilane is Formula I: 【Chemistry 1】 (In the formula, R ａ = a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms, x=0 to 2, R=H ３ C-(CH ２ ) ｙ (y = 0 to 2). a monomeric alkylsilane of -Formula II: 【Chemistry 2】 wherein R=a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms; R １ =H ３ C-(CH ２ ) ｙ (y=0~2)、 X=H ３ C- or H ３ C-(CH ２ ) ｙ O-(y=0-2), n = 0 to 20. a linear oligomeric alkylsilane of -Formula III: 【Transformation 3】 wherein R=a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms; R １ =H ３ C-(CH ２ ) ｙ (y=0~2)、 X=H ３ C- or H ３ C-(CH ２ ) ｙ O-(y=0-2), n=0 to 20, m = 0 to 20. a branched oligomeric alkylsilane of -Formula IV: 【Chemistry 4】 wherein R=a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms; R １ =H ３ C-(CH ２ ) ｙ (y=0~2)、 X=H ３ C- or H ３ C-(CH ２ ) ｙ O-(y=0-2), n = 0 to 20. or a cyclic oligomeric alkylsilane of mixtures of monomeric alkylsilanes of formula I with linear, branched and / or cyclic oligomeric alkylsilanes of formula II, formula III and / or formula IV 1. A liquid adhesive composition selected from:

2. At least one of the alkylsilanes is Formula I: 【Transformation 5】 (In the formula, R ａ = a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms, x=0 to 2, R=H ３ C-(CH ２ ) ｙ (y = 0 to 2). a monomeric alkylsilane of -Formula II: 【Transformation 6】 wherein R=a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms; R １ =H ３ C-(CH ２ ) ｙ (y=0~2)、 X=H ３ C- or H ３ C-(CH ２ ) ｙ O-(y=0-2), n = 0 to 20. a linear oligomeric alkylsilane of a mixture of monomeric alkylsilanes of formula I and linear oligomeric alkylsilanes of formula II 2. The liquid adhesive composition of claim 1, wherein the liquid adhesive composition is selected from the group consisting of:

3. 2. The liquid adhesive composition of claim 1, wherein the at least one alkyl silane is selected from propyltrimethoxysilane, propyltriethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, oligomeric alkoxysilanes (e.g., Dynasylan® SIVO 502), or mixtures thereof.

4. 10. The liquid adhesive composition of claim 1, wherein the carbon content of said at least one hydrophobized fumed silica ranges from 0.4 to 3.0 wt. %.

5. 10. The liquid adhesive composition of claim 1, wherein the carbon content of said at least one hydrophobized fumed silica ranges from 0.4 to 2.0 wt. %.

6. 10. The liquid adhesive composition of claim 1, wherein the total mass of the at least one hydrophobized fumed silica ranges from 1 to 30% by weight of the total mass of the liquid adhesive composition.

7. 2. The liquid adhesive composition of claim 1, wherein the total mass of the at least one hydrophobized fumed silica ranges from 2 to 10% by weight of the total mass of the liquid adhesive composition.

8. 2. The liquid adhesive composition of claim 1, wherein the total mass of the at least one alkylsilane is in the range of 5 to 60 wt. % of the total mass of the at least one hydrophobized fumed silica contained in the liquid adhesive composition.

9. 2. The liquid adhesive composition of claim 1, wherein the total mass of the at least one alkyl silane is in the range of 20 to 40 wt. % of the total mass of the at least one hydrophobized fumed silica contained in the liquid adhesive composition.

10. The liquid adhesive composition of claim 1 , wherein at least one of said base polymers is an epoxy resin.

11. 10. A method for making a liquid adhesive composition according to claim 1, comprising at least one base polymer, at least one hydrophobized fumed silica, and at least one alkylsilane; - mixing at least one of said base polymers, at least one of said hydrophobized fumed silicas, at least one of said alkylsilanes and, optionally, other components of said liquid adhesive composition. A method comprising:

12. A liquid adhesive composition obtainable by the method of claim 11.

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