DD207102A3 - METHOD FOR PRODUCING SOLID POLYURETHANOUS ADHESIVES - Google Patents

Abstract

The invention relates to the preparation of a good crystallizing polyurethane adhesive in the reaction extruder. The aim of the invention is to produce polyurethane adhesive effectively, which have excellent Adhaesionseigenschaften, a high initial adhesion and a residue-free and rapid Loeslichkeit in weakly polar solvents. According to the process of the invention adhesives based on 4,4'-diphenylmethane diisocyanate and Polyhexamethylenglykoladipinat, synthesized in a ratio range (NCO / OH ratio) of 0.85 to 1.08 and a Urethangruppengehalt of not more than 8 mol percent, prepared for processability the reaction extruder. The adhesive according to the invention is used as a special adhesive in the shoe industry.

Description

232642 k

Title of the invention

Process for the preparation of solid polyurethane adhesives

Field of application of the invention

The invention relates to a process for the preparation of a good crystallizing polyurethane adhesive in the reaction extruder. The adhesive, which is processed as a two-component system, is readily soluble in weakly polar solvents and is used to bond elastic and rigid materials such as leather, artificial leather, textiles, paper, rubber, plastics and the like. A special field of application is the shoe industry, since the adhesive is characterized by sufficient Ablüftzeiten and short pressing time by excellent initial strength.

Characteristic of the known technical solutions

nothing is known about the preparation of two-component adhesive raw materials by the reaction extruder process, that is to say with the exclusion of solvents.

De &'prior art represents a three-stage process, which is described in the FRG - AS 2 149 S3o. Accordingly, the synthesis proceeds on the basis of customary raw materials in the first reaction stage in the presence of nonpolar or weakly polar solvents. In the second. Stage is a thermal aftertreatment of the solution at preferably 70 ⁰ C to 90 ⁰ C for 12 to 72 hours until no more free isocyanate is detectable. Finally, in the third phase, the solvent changes over at reduced pressure and elevated temperature

discharged a vacuum Ausdampfschnecke. The products prepared by this process are naturally readily soluble in those types of solvents in the presence of which they were synthesized in the first reaction stage. Even from the presentation of the method and the description of the technical means it appears that it is relatively expensive. Older, but as far as their reproducibility strong unsettled technical procedures are such nature as they z. As described in WP 195 140. Accordingly, a reaction mixture discharged via a mixing head onto a heated endless belt after granulation and intermediate storage is granulated and formulated.

The requirement for solubility in weak, polar solvents is contrary to the prior art, only the isocyanate tolylene diisocyanate contrary "crystallization kinetic studies by X-ray diffraction underline the clearly most favorable condition of a recipe based on tolylene diisocyanate for the reaction extruder» The practice confirmed, however, that such formulations, although in technological Multi-stage process are manageable, but are not producible on the one-stage reaction struc- ture due to poor crystallization, low conversion rates and insufficient adhesion properties.

The Srfi

The object of the invention is, in a reaction extruder and consequently in an effective manner, to prepare polyurethane adhesives which have excellent adhesion properties, a high initial adhesion strength and a residue-free and rapid solubility in weakly polar solvents.

presentation; the essence of the invention

The object of the invention is to develop a process for the synthesis of solid polyurethane adhesives in which customary and available components are used in such a quantitative ratio as reaction partners in polyurethane urethane chemistry.

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be set that a polyurethane adhesive is formed with the properties mentioned in the Zielstellang, which must have a high crystallizability and the contradiction to the type of solvent used of the product to be packaged and the "technologically justified requirement for good initial adhesion of the bond is to resolve.

Surprisingly, it was found that a receptor based on 4 _} 4'-diphenylmethane diisocyanate and Polyhexamethylengiykoladipinat synthesized in a performance ratio range (ITCO / OH ratio) of 0.85 to .φ, Οβ and a Urethangruppengehalt of not more than 8 mol / S a good Processability ensured on the reaction extruder at surprisingly high release and adhesion properties of the finished product. In this case, the urethane group content in the range of 5 to 8 mol% can be varied either starting from the molecular weight of the polyhexamethylene glycol adipinate and / or by proportionate addition of a low low molecular weight diol content. As the diol may be preferably used: 1,4-butanediol; 1,6-hexanediol or mixtures of these two diols.

Starting from the desired dynamic viscosity of the product and its molecular weight (usually the characteristic viscosity), conventional additives such as accelerators, catalysts, chain regulators and inhibitors can be used.

For the polyhexamethylene glycol adipate having a molecular weight of 1000 to 3000, preferably 1500 to 2200, an acid value ~ 1.0 mg KOH / g, preferably ^ 0.5 mg ECH / g is necessary. Optionally, acid-diminishing carbodiimides, preferably H, U ¹ -diphenyl-2,2 ', 4,4'- (or 6,6') -tetraisopropylcarbodiimide, can be added to the polyester in quantities of from 0.7 to 1.7% by mass.

Lurch the process of the invention, it is possible to produce polyurethane adhesives in the reaction extruder in an effective manner »These adhesives are characterized by excellent adhesion properties, a high initial adhesion, as well as by a residue-free and rapid solubility in weakly polar solvents,

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The invention will be explained in more detail below with reference to two exemplary embodiments:

Embodiment 1

In a reservoir, a polyhexamethylene glycol adipate with the average molecular weight of 1500, a GH number of 74.5, an acid number of 0.54 and a water content of 0.02 % with the primary alcohol n-decanol as chain limiter in a concentration of 1 , 11 ml / kg polyol homogeneously mixed and tempered to 90 ⁰ G. In a second stirred tank 4,4'-diphenylmethane diisocyanate (MDI), whose UCO content to. 33.49 % and its clear point with 40.8 ⁰ C were determined, also at 90 ⁰ C submitted. By means of two precision metering pumps 25 118 g of Polyol-Gem.isch.es and 4334 g of MDI are fed with 90 ⁰ G continuously a mixing unit per hour.

The UCO / OH ratio at the mixing head is 1.008. The incoming components are intensively mixed during a mean residence time of 0.85 minutes at high shear rates. As a result of the released heat of reaction and the mechanical mixing energy, the melt heats up to approx 238 G. The mixing head is mounted on a reaction extruder, from whose screw channels the emerging melt is directly taken up and conveyed on. The polyurethane melt is further homogenized and reacts at a falling to 160 C temperature on, and is finally after a residence time of 3 ₅ 9 sin in a mold to strands of 3 ... 5 mm 0 squeezed out.

The strands are pulled through a cooling water bath (water temperature 22 ⁰ C), where they can be granulated after a cooling time of 100 s in a crystallized state. The granules are uniform and completely free-flowing.

Samples of the granules are analyzed immediately after removing the adhering cooling water. The! ICO re stgehalt is b 0.064 %, the characteristic viscosity is <

at

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Bine solution of 20% solids in ethyl acetate has a dynamic viscosity of 4820 mPa.s. A completely homogeneous solution was achieved in a 1 kg batch already after a stirring bz-w, dissolution time of 3 hours, viscosity changes over time were not observed even after 6 months. The samples remained free of insoluble components (gels). The product dissolved in ethyl acetate is mixed with 3 % hardener (polymethylenepolyphenyl isocyanate) with a pot life of over 20 hours and tested according to TGL 28 240/05 using the artificial leather / synthetic rubber (medium hard) specimen combination, without any pretreatment of the specimen.

Initial adhesion (H / cm): 1.6 after 1 minute of compression molding

Peel strength (I / cm): 6.7

Peel strength (U / cm): 8.9

after hydrolysis (sample storage for 24 h in de water)

Embodiment 2

In a storage container is a Polyhexamethylenglykoladipinat with an average molecular weight of 2000, an OH number of 56.9, an acid number of 0, '34 and a water content of 0.009 % with n-decanol as a chain delimiter in a concentration of 1.11 ml / kg Polyol and 1,4-butanediol homogeneously mixed in a concentration of 12.78 g / kg polyol and heated to 90 ⁰ G. In one, second stirred tank is 4 _} 4 ^! -Diphenylmethandiisocyanat (MDI), whose liCO- was determined to 33.47% 'and its clear point with 40.8 ⁰ G, also at 90 ⁰ C submitted. By means of two precision metering pumps, 25 759 g of the polyol mixture and 4003 g of the MDI are fed per hour to a mixing unit.

of the polyol mixture and 4003 g of the MDI each with 90 ⁰ C continuously

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The ICO / OH ratio at the mixing head inlet is 0.958. The entering components are mixed intensively during a mean residence time of 0.85 min at high shear rates, -Infolge the -freiwerdenden heat of reaction and the registered mechanical mixing energy, the melt is heated to the mixing head outlet to circa indication 235 ⁰ C. The mixing head is mounted on a Reaction extruder mounted on whose screw channels the exiting melt is directly absorbed and further promoted »The polyurethane melt is further homogenized and reacts at a falling to 16O ⁰ C temperature continues, and finally after a residence time of 3.9 min in a mold extruded into strands of 3 ... 5 mm 0.

The strands are pulled through a Kiihlwasserbad (water temperature 22 ⁰ C) können.- apparatus where they crystallize after a cooling time-von'100 in a / granulated state The granulate is uniform and perfectly free-flowing ·

Samples of the granules are analyzed immediately after removing the adhering cooling water. The ICO residual content is 0.05 % by weight , the characteristic viscosity is 0.71 %, and the solution of 20% solid in ethyl acetate has a dynamic viscosity of .348G mPa.s.

A completely homogeneous solution was added. a 1 kg batch already after a stirring or *. Dissolution time of 3 hours achieved. Viscosity changes over ^; the time was not observed even after 6 months.,

The samples remained free of insoluble components (gels), that in ethyl acetate. dissolved product is mixed with 3 % hardener (Polymethylenpolyphenylisocyanat), the pot life is more than 20 h, and accordingly, the TGL 28 240/05 using the test specimens artificial leather / synthetic rubber (medium hard), without any test specimen pretreatment, tested ..

Initial adhesion strength (U / cm) .:. 1.1

after 1 min. Pressing pressure . ,

Peel strength (I / cm): 8.6

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Peel strength (U / cm): after hydrolysis (sample storage 24 yes. In aest. Water)

9.4

Claims (1)

-β- 232 6 42 L Brf claim A process for the preparation of solid polyurethane adhesives by the reaction extruder process, according to which an adhesive is formed, which is soluble in weakly polar solvents and is characterized by good crystallization and adhesion, in particular initial adhesion, characterized in that 4.4 ^! -Diphen2rlmethandiisocyanat with Polyhexamethylenglykoladipinat with a molecular weight of 1000 to 3000 ,. preferably 1500 to 2200 and an acid number of ^ 1.0 mg KOH / g, preferably ^ 0.5 mg KOH / g in an ICO / OH ratio of 0.85 to -ί, -98 ,. at a urethane group content of 5 to a maximum of 8 mol%, wherein the urethane group content is determined by molecular weight variation of the polyhexamethylene glycol adipinate and / or by proportionate addition of a low molecular weight (up to a maximum of 0.45 mole based on one mole of polyester alcohol) of the diol portion.