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EP-4741467-A1 - A HOT-MELT ADHESIVE HAVING IMPROVED HEAT STABILITY

EP4741467A1EP 4741467 A1EP4741467 A1EP 4741467A1EP-4741467-A1

Abstract

The invention relates to an adhesive composition comprising: a) At least one polymer P, b) A stabilizer S comprising b1) At least one first stabilizer S1 and b2) At least one second stabilizer S2, which is different from the at least one stabilizer S1 wherein the first stabilizer S1 is a non-sulfur containing compound having at least two phenolic groups and the second stabilizer S2 is a sulfur containing compound.

Inventors

  • TEPELMANN, Weng

Assignees

  • Sika Technology AG

Dates

Publication Date
20260513
Application Date
20241107

Claims (17)

  1. An adhesive composition comprising: a) At least one polymer P, b) A stabilizer S comprising: b1) At least one first stabilizer S1 and b2) At least one second stabilizer S2, wherein the first stabilizer S1 is a non-sulfur containing compound having at least two phenolic groups and the second stabilizer S2 is a sulfur containing compound.
  2. The adhesive composition according to claim 1, wherein the first stabilizer S1 has a molecular weight determined by gel permeation chromatography (GPC) using polystyrene as standard of not more than 2500 g/mol, preferably not more than 2000 g/mol, particularly 150 - 2000 g/mol, especially 250 - 1500 g/mol.
  3. The adhesive composition according to claim 1 or 2, wherein the second stabilizer S2 has a molecular weight determined by gel permeation chromatography (GPC) using polystyrene as standard of not more than 2000 g/mol, preferably not more than 1500 g/mol, particularly 100 - 1500 g/mol, especially 200 - 1000 g/mol.
  4. The adhesive composition according to any one of previous claims, wherein the first stabilizer S1 is a non-sulfur containing ester type compound having at least two phenolic groups and/or the second stabilizer S2 is a sulfur containing ester type compound.
  5. The adhesive composition according to any one of previous claims, wherein the first stabilizer S1 selected from ethylenebis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate] and pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate).
  6. The adhesive composition according to any one of previous claims, wherein the second stabilizer S2 is thiodiethylene bis[3-(3,5-di-tert.-butyl-4-hydroxyphenyl)propionate] or a compound of formula (I) where R 1 and R 2 are independently of each other linear or branched C 10 to C 22 alkyl groups, preferably linear or branched C 12 to C 20 alkyl groups.
  7. The adhesive composition according to any one of previous claims, wherein the compound of formula (I) is selected from dilauryl 3,3'-thiodipropionate, distearyl thiodipropionate, dimyristyl thiodipropionate, and ditridecyl thiodipropionate, especially dilauryl 3,3'-thiodipropionate.
  8. The adhesive composition according to any one of previous claims, wherein weight ratio of the at least one first stabilizer S1 to the at least one second stabilizer S2 is in the range of from 10:1 to 10:1, preferably from 5:1 to 1:5.
  9. The adhesive composition according to any one of previous claims, wherein the adhesive composition is a hot-melt adhesive, preferably having a softening point determined by the Ring & Ball method as defined in ISO 4625-1:2020 standard of at or above 85 °C, preferably at or above 105 °C.
  10. The adhesive composition according to any one of previous claims, wherein the adhesive composition is a polyolefin-based hot-melt adhesive, a rubber-based hot-melt adhesive, or a polyurethane-based hot-melt adhesive.
  11. The adhesive composition according to any one of previous claims, wherein the adhesive composition is a polyolefin-based hot-melt adhesive and the at least one polymer P is selected from at 25 °C solid non-functionalized and functionalized polyolefins, particularly from at 25 °C solid non-functionalized and functionalized poly-α-olefins, especially from at 25 °C solid non-functionalized and functionalized amorphous poly-α-olefins (APAOs).
  12. The adhesive composition according to any one of claims 1-10, wherein the adhesive composition is a rubber-based hot-melt adhesive and the at least one polymer P is a styrene block copolymer, preferably selected from styrene-isoprene diblock (SI) copolymers, styrene-isoprene-styrene triblock (SIS) copolymers, styrene-butadiene diblock (SB) copolymers, styrene-butadiene-styrene triblock (SBS) copolymers, styrene-isoprene-butadiene-styrene block copolymers (SIBS), styrene-ethylene-butadiene-styrene (SEBS) block copolymers, styrene-ethylene-propylene-styrene block (SEPS) copolymers, and styrene-ethylene-ethylene-butylene-styrene copolymers (SEEPS).
  13. The adhesive composition according to any one of claims 1-10, wherein the adhesive composition is a polyurethane-based hot-melt adhesive and the at least one polymer P is an isocyanate- and/or silane-functionalized polyurethane polymer.
  14. Use of the adhesive composition according to any one of previous claims as an automotive assembly adhesive, laminating adhesive, or as an adhesive for the building of sandwich elements.
  15. A method for adhesively bonding a first substrate to a second substrate, the method comprising steps of: I) Heating an adhesive composition according to any one of claims 1-13 to provide a melted adhesive composition, II) Applying the melted adhesive composition to a surface of the first substrate, III) Contacting the applied adhesive with a surface of the second substrate, and IV) Physically curing the applied adhesive by cooling and/or chemically curing the applied adhesive with water, preferably with atmospheric moisture.
  16. Use of a stabilizer SB for improving the heat stability of an adhesive composition, preferably a hot-melt adhesive composition, wherein the stabilizer SB comprises: b1) At least one first stabilizer SB1 and b2) At least one second stabilizer SB2, wherein the first stabilizer SB1 is a non-sulfur containing compound having at least two phenolic groups and the second stabilizer SB2 is a sulfur containing compound.
  17. Use according to claim 16, wherein the first stabilizer SB1 is the first stabilizer S1 as defined in any one of claims 1-13 and/or the second stabilizer SB2 is the second stabilizer S2 as defined in any one of claims 1-13.

Description

Technical field The invention relates to hot-melt adhesives having improved heat stability and to use of such adhesives as an assembly adhesive, a laminating adhesive, or as an adhesive for the building of sandwich elements, particularly in automotive industry. Background of the invention Hot-melt adhesives are solvent free adhesives, which are solid at room temperature and which are applied to the substrate to be bonded in form of a melt. After cooling the adhesive solidifies and forms an adhesive bond with the substrate through physically occurring bonding. Conventional hot-melt adhesives are non-reactive adhesives, which soften again upon heating and are, therefore, not suitable to be used at elevated temperatures. Hot-melt adhesives also include pressure sensitive adhesives (HM-PSA), which are permanently tacky adhesives that are applied as a melt. Non-reactive hot-melt and hot-melt PSA adhesives typically contain a basic polymer matrix comprising amorphous polyolefins, particularly poly-α-olefins or thermoplastic elastomers (TPE), especially styrene block copolymers, and additives, such as tackifying resins, waxes and/or liquid polyolefin resins. Reactive hot-melt adhesives contain polymers with reactive groups that enable chemical curing of the adhesive, for example, by crosslinking of the polymer chains. Due to the chemically cured polymer matrix reactive hot-melt adhesives do not soften upon heating and these adhesives are, therefore, suitable for use also at elevated temperatures. The chemical curing of the polymers can be initiated, for example, by heating or exposing the adhesive composition to water, such as atmospheric moisture. Moisture curing hot-melt adhesives typically contain polymers, for example, polyolefins or polyurethane polymers, which are functionalized with isocyanate or silane groups that enable crosslinking of the polymer chains upon contact with atmospheric moisture. Moisture curing polyurethane hot-melt (PUR-RHM) adhesives consist mainly of isocyanate-functional polyurethane polymers, which have been obtained by reacting suitable polyols, typically polyester and/or polyether polyols, with polyisocyanates, where the reaction is conducted at a molar excess of isocyanate (NCO) groups over hydroxyl (OH) groups. The adhesive composition is cured by reaction of the residual isocyanate groups with water, which results in various chain extension and/or crosslinking reactions of the polymers. A fully cured polyurethane hot-melt adhesive comprises urea and/or urethane bonds and, depending on the starting materials used for providing the isocyanate-functional polymer, ester and/or ether bonds. The reactive polyolefin-based hot-melt adhesives are typically one-component moisture curable compositions containing as the main polymer component silane-functionalized poly-α-olefins, such as silane grafted poly-α-olefins. Such silane-functionalized poly-α-olefins can be obtained, for example, in a process comprising grafting an olefinically unsaturated alkoxysilanes to poly-α-olefins in the presence of a free-radical initiator, such as peroxide. Silane-functionalized poly-α-olefins are commercially available from various suppliers. The crosslinking of the silane grafted poly-α-olefin is accomplished by hydrolyzing the alkoxy silane groups by water followed by dehydrocondensation of the silanol groups, resulting in release of methanol and water. A general disadvantage of both reactive and non-reactive hot-melt adhesives is that non-cured adhesive compositions have relatively low thermal stability, which limits their use in high temperature applications. One example of such applications is a roller coating process, where the adhesive composition may remain for several minutes in a molten state before being placed between the coating rolls to be applied on a surface of a substrate. In case of insufficient thermal stability, the viscosity of the adhesive may increase to a level, which eventually prevents the application with the rolls. Furthermore, adhesives exhibiting a low thermal stability may change their color from clear to yellow and/or exhibit "angel hairs" and/or "black stains" when stored at high temperatures. Such behavior typically results from degradation of the polymeric constituents of the adhesive and/or from unwanted chemical reactions induced by the application of thermal energy. Changes in appearance of the non-cured or cured adhesive are typically not acceptable, even though they would not have any effect on the performance related properties of the adhesive. It is well known that thermal stability of hot-melt adhesives can be improved by using specific antioxidants, also known as heat stabilizers, such as sterically hindered phenolic antioxidants. These are commercially available from various providers, for example, under the trade name of Irganox®, Tinuvin®, and Irgafos® (all from BASF). However, in many cases the use of common antioxidants results only in minor improvement of th