DE102012200018A1 - Reactive polyurethane preparations - Google Patents

Abstract

The invention relates to reactive polyurethane systems having improved properties and to preparations which comprise these polyurethane systems, to processes for preparing these polyurethane systems or preparations and to their use, for example, as hot-melt adhesives.

Description

The invention relates to polyurethane-containing hotmelt adhesives having improved properties and to compositions which comprise these hotmelt adhesives, to processes for producing the hotmelt adhesives or to the preparations and to their use.

In particular, the present invention relates to polyurethane-containing hot melt adhesives (hereinafter also referred to as hot melt adhesive systems or PUR hotmelts) which comprise asymmetric diisocyanates and low-monomer prepolymers. Another object of the present invention are preparations which contain the hot melt adhesives, processes for the preparation of hot melt adhesives or preparations and their use.

Reactive polyurethane hotmelts are a rapidly growing product group within the application of polyurethanes in the adhesives field. For their construction, preference is given to using linear polyester and / or polyether polyols in combination with an excess of polyisocyanates, preferably diisocyanates.

The advantages of this class of product, especially in the absence of solvent, the ability to apply the products in the heat with relatively low viscosities, still get high initial strength and after a relatively short time due to the further reaction with moisture adhesive bonds with very high, well over to maintain the application temperatures lying heat and excellent solvent resistance.

In order to quickly establish initial strength, reactive PUR hotmelts use polyols whose concentration in the hotmelt is sufficiently high and whose first or second order transition (Tm or Tg) is at relatively high temperatures. Care should be taken here that the first or second order transition also takes place in a formulated hotmelt and not by e.g. Miscibility of the crystallizing polyol is suppressed in the overall system.

Since the reactive PUR hotmelt is typically applied as a melt, the application temperature must be above the transition temperature of the formulated hotmelt. The transition temperatures can be relatively high depending on the formulation. Application temperatures of well over 100 ° C are common.

Important methods for determining initial strengths are the measurement of the open time (OZ) and the setting time (AZ).

The OZ describes the period of time within which the seemingly dry adhesive layers can still be joined together, without having to accept losses in the final strength of the executed bond.

The AZ describes the time after which the bond has built sufficiently high strength to cancel the pressing pressure and thus the fixation of the parts to be bonded.

From the end user's point of view, in principle reactive hot melt adhesive systems are desirable which can be applied at low temperatures without having to accept losses in AZ and / or OZ.

The skilled worker is aware that by using suitable polyols or polyol mixtures, the application temperature of hot melt adhesives can be reduced. This can be done, for example, in which polyols or polyol mixtures are used with lower melt viscosities. Typically, however, the AZ and the OZ are characterized by the polyol mixture. When changing the polyol mixture therefore often the cooling behavior of the hot melt adhesive, possibly by adding appropriate additives, be elaborately adjusted. Longer development times are the result.

After the apprenticeship of DE-A 101 63 857 By using asymmetric diisocyanates, it is possible to prepare compositions which are distinguished by lower melt viscosities at the same temperatures compared to systems of the prior art. The AZ and the OZ remain unaffected.

The EP-A 0 693 511 describes reactive hot melt systems with low initial viscosity and shorter open times. By using asymmetric diisocyanates, hot-melt systems can be produced which, compared to standard systems based on symmetrical diisocyanates, such as, for example, 4,4'-MDI, have more rapid initial strengths. From the teaching is not clear how and whether the AZ and OZ change when the application temperatures are reduced.

The problem underlying the invention was therefore in particular to provide systems whose application temperatures are lower than the previously known formulations of reactive polyurethane hotmelts, without causing any changes in the OZ or AZ.

It has now surprisingly been found that the application temperature of hot melt adhesive systems based on crystalline or semicrystalline polyesterpolyols or mixtures thereof with crystalline, partially crystalline, amorphous, liquid polyols or other components and asymmetric isocyanates can be significantly reduced in comparison with formulations of the prior art, without that changes in the AZ or OZ result.

The present invention thus relates to reactive polyurethane systems comprising (a) NCO prepolymers based on asymmetric isocyanates or mixtures of asymmetric isocyanates and also (b) prepolymers with a content of free monomeric isocyanate of <1% by weight.

The reactive polyurethane systems according to the invention generally have a viscosity at 130 ° C. of <10000 mPas, preferably of <8000 mPas and particularly preferably of <5000 mPas. In addition, they have a residual monomer content of less than 1% by weight, preferably less than 0.5% by weight, preferably less than 0.1% by weight (determination methods see experimental part of the present application).

The present invention also provides the use of these reactive polyurethane systems comprising (a) NCO prepolymers based on asymmetric isocyanates or mixtures of asymmetric isocyanates and (b) prepolymers having a content of free monomeric isocyanate of <1 wt .-% in hot melt adhesives to reduce those application temperatures.

The asymmetric isocyanate used in the reactive polyurethane systems of the invention is preferably 2,4'-MDI.

• (A) mindestens einem monomeren aromatischen, aliphatischen, araliphatischen und/oder cycloaliphatischen Diisocyanat, dessen Isocyanatgruppen unterschiedliche Reaktivitäten gegenüber Polyolen besitzt oder ein über freie NCO-Gruppen verfügendes, auf diesen monomeren Diisocyanaten aufgebautes Prepolymer und
• (B) ein Polyol oder Polyolgemisch wobei das Verhältnis von A zu B so gewählt wird, dass das molare Verhältnis von NCO zu OH > 1 beträgt, und anschließend wird das Umsetzungsprodukt aus (A) und (B) mit einem Isocyanatterminierten Prepolymer gemischt, welches einen Gehalt an freiem monomeren Isocyanat von < 1 Gew.-%, bevorzugt < 0,5 Gew.-% und besonders bevorzugt < 0,1 Gew.-% verfügt.

The reactive polyurethane systems according to the invention are obtainable by reaction of

• (A) at least one monomeric aromatic, aliphatic, araliphatic and / or cycloaliphatic diisocyanate whose isocyanate groups have different reactivities to polyols or a prepolymer having free NCO groups and based on these monomeric diisocyanates
• (B) a polyol or polyol mixture wherein the ratio of A to B is chosen so that the molar ratio of NCO to OH> 1, and then the reaction product of (A) and (B) is mixed with an isocyanate-terminated prepolymer, which a content of free monomeric isocyanate of <1 wt .-%, preferably <0.5 wt .-% and particularly preferably <0.1 wt .-% has.

The invention also relates to preparations which contain the reactive polyurethane systems according to the invention, and to the use of the reactive polyurethane systems or preparations according to the invention for example in sealants, coatings, foams, and in adhesives, in particular in hotmelt adhesives. Another object of the present invention is a process for the preparation of the inventive reactive polyurethane systems and / or preparations.

Isocyanate component A):

Isocyanates suitable as isocyanate component A) are, for example, those having isocyanate contents of from 5 to 60% by weight (based on the isocyanate) with aliphatically, cycloaliphatically, araliphatically and / or aromatically bound isocyanate groups, such as, for example, 1,4-diisocyanatobutane, 1,6- Diisocyanatohexane (HDI), 2-methyl-1,5-diisocyanatopentane, 1,5-diisocyanato-2,2-dimethylpentane, 2,2,4- and 2,4,4-trimethyl-1,6-diisocyanatohexane, respectively , 10-diisocyanatodecane, 1,3- and 1,4-diisocyanatocyclohexane, 1,3- and 1,4-bis- (isocyanatomethyl) -cyclohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane ( Isophorone diisocyanate, IPDI), 4,4'- Diisocyanatodicyclohexylmethane, 1-isocyanato-1-methyl-4 (3) isocyanatomethylcyclohexane, bis (isocyanatomethyl) norbornane, 1,3- and 1,4-bis (2-isocyanato-prop-2-yl) -benzene (TMXDI ), 2,4- and / or 2,6-diisocyanatotoluene (TDI), 2,2'-, 2,4'- and / or 4,4'-diisocyanatodiphenylmethane (MDI), 1,5-diisocyanatonaphthalene, 1, 3- and 1,4-bis (isocyanatomethyl) benzene or mixtures of these. Of course, polyisocyanates can also be used.

Preferred diisocyanate component A) diisocyanates are those which have differently reactive NCO groups. Examples of such components are 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI), 2,4-diisocyanatotoluene (TDI) or 2,4'-diisocyanatodiphenylmethane (MDI).

Diisocyanate component A) particularly preferred diisocyanate is 2,4'-diisocyanatodiphenylmethane (MDI).

Polyol component B):

In the context of the present invention, a polyol is understood as meaning a polyol having more than one OH group, preferably two terminal OH groups. Such polyols are known to the person skilled in the art. Preference is given to polyester polyols. They can be prepared by known methods, for example from aliphatic hydroxycarboxylic acids or from aliphatic and / or aromatic dicarboxylic acids and one or more diols. It is also possible to use corresponding derivatives, e.g. Lactones, esters of lower alcohols or anhydrides. Examples of suitable starting materials are succinic, adipic, suberic, azelaic, sebacic, dodecanedioic, glutaric, glutaric, phthalic, isophthalic, terephthalic, phthalic, ethylene glycol, diethylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, ε-caprolactone ,

Polyester polyols are either liquid at room temperature (glass transition temperature Tg <20 ° C) or solid. Solid at room temperature polyester polyols are either amorphous (glass transition temperature Tg> 20 ° C) or crystallizing.

Suitable crystallizing polyesters are, for example, those based on linear aliphatic dicarboxylic acids having at least 2 carbon atoms, preferably at least 6 carbon atoms, more preferably 6 to 14 carbon atoms in the molecule, e.g. Adipic acid, azelaic acid, sebacic acid and dodecanedioic acid, preferably adipic acid and dodecanedioic acid and linear diols having at least 2 carbon atoms, preferably at least 4 carbon atoms, more preferably 4-6 carbon atoms in the molecule, preferably with an even number of carbon atoms such as 1,4-butanediol and 1 , 6-hexanediol. Likewise, the polycaprolactone derivatives based on bifunctional starting molecules such as 1,6-hexanediol are particularly suitable.

Examples of suitable amorphous polyester polyols are those based on adipic acid, isophthalic acid, terephthalic acid, ethylene glycol, neopentyl glycol and 3-hydroxy-2,2-dimethylpropyl-3-hydroxy-2,2-dimethylpropanoate.

Suitable polyester polyols which are liquid at room temperature are, for example, those based on adipic acid, ethylene glycol, 1,6-hexanediol and neopentyl glycol.

Suitable polyetherpolyol are the polyethers customary in polyurethane chemistry, for example those using diacidic or hexahydric starter molecules such as, for example, water, ethylene glycol, 1,2- or 1,3-propylene glycol, neopentyl glycol, glycerol, trimethylolpropane, pentaerythritol, sorbitol or 1- to 4-NH-bond-containing amines prepared addition or Mischadditionsverbindungen of tetrahydrofuran, styrene oxide, ethylene oxide, propylene oxide, the butylene oxides or epichlorohydrin, preferably of ethylene oxide and / or propylene oxide. Preferably, the bifunctional propylene oxide and / or ethylene oxide adducts and polytetrahydrofuran be mentioned. Such polyether polyols and their preparation are known in the art.

The preparation of the reactive polyurethane systems and / or preparations according to the invention is carried out, for example, by mixing the polyol components B) with an excess of polyisocyanates A), the ratio of A to B being selected such that the molar ratio of NCO to OH> 1 , is preferably from 1.1 to 2.0, particularly preferably from 1.2 to 1.8, and is stirred until a constant NCO value is obtained, then an isocyanate-terminated prepolymer which has a content of free Isocyanate of <1 wt .-%, preferably <0.5 wt .-%, particularly preferably <0.1 wt .-% has, is mixed and then bottled.

The reaction temperature is 60 to 150 ° C, preferably 80 to 130 ° C, is selected. Of course, the preparation of the reactive polyurethane systems and / or preparations can also be carried out continuously in a stirred tank cascade or suitable mixing units, such as, for example, high-speed mixers according to the rotor-stator principle or a static mixer.

It is of course possible, the polyester and / or polyether or some of them with a deficit of diisocyanates, preferably 1,6-diisocyanatohexane (HDI), 2,4- and / or 2,6-diisocyanatotoluene (TDI) and / or 2,4'- and / or 4,4'-diisocyanatodiphenylmethane (MDI), to modify and react after completion of the reaction, the urethane group-containing polyols with an excess of diisocyanates to a hotmelt containing isocyanate groups.

It is also possible to react the polyols with the diisocyanates in the presence of up to 5% by weight of, for example, trimers of aliphatic diisocyanates, e.g. HDI perform or add such Trimerisate after completion of prepolymerization.

If desired, the reaction of the polyols with the diisocyanates can also take place in the presence of catalysts. In question are the known to those skilled, commonly used in polyurethane chemistry catalysts.

In addition to the reactive polyurethane systems and / or preparations according to the invention, the preparations may also be provided with customary additives. Corresponding additives can be selected, for example, from the group consisting of the reaction with moisture-activating catalysts, further inorganic or organic fillers, dyes, resins, reactive and non-reactive polymers and extender oils.

The reactive polyurethane systems and / or preparations according to the invention can be used in a variety of ways, for example in sealants, coatings, foams, in adhesives, in particular in hotmelt adhesives, as assembly adhesives, for example for provisional or final fixing of components, as bookbinding adhesive, as adhesive for the production of cross-bottomed valve sacks. for the production of composite films and laminates or as Kantenumleimer can be used.

Examples

Unless otherwise noted, all percentages are by weight. In the examples and comparative examples, the following raw materials were used:

Polyester A:

Polyesterpolyol based on adipic acid and 1,6-hexanediol having a hydroxyl number of about 30 mg KOH / g and an acid number of about 0.5 mg KOH / g. The preparation takes place in a manner known to those skilled in the art and is described for example in Ullmanns Enzyklopadie der technischen Chemie, "Polyester", 4th edition, Verlag Chemie, Weinheim, 1980 ,

Polyester B:

Polyester polyol based on adipic acid, isophthalic acid, neopentyl glycol and ethylene glycol having a hydroxyl number of about 55 mg KOH / g and an acid number of about 0.5 mg KOH / g. The preparation takes place in a manner known to those skilled in the art and is described for example in Ullmanns Enzyklopadie der technischen Chemie, "Polyester", 4th edition, Verlag Chemie, Weinheim, 1980 ,

Polyester C:

Polyester polyol based on 1,12-dodecanedioic acid and 1,6-hexanediol having a hydroxyl number of about 30 mg KOH / g and an acid number of about 1.0 mg KOH / g. The preparation takes place in a manner known to those skilled in the art and is described for example in Ullann's Encyclopedia of Industrial Chemistry, "Polyester", 4th Edition, Verlag Chemie, Weinheim, 1980 ,

Polyether A

Desmophen ^® 1262 BD, Bayer MaterialScience AG, Leverkusen, Germany.

Isocyanate I-1:

Desmodur ^® 44M, 4,4'-diisocyanate, Bayer MaterialScience AG, Leverkusen, Germany.

Isocyanate I-2:

Desmodur ^® E XP 2715, Bayer MaterialScience AG, Leverkusen, Germany.

Isocyanate I-3:

Desmodur ^® VP LS 2397, Bayer MaterialScience AG, Leverkusen, Germany.

Stabilizer A

Irganox ^® 1010, Ciba Specialty Chemicals Inc., Basel, CH.

Preparation of Comparative Example 1

Comparative Example 1 corresponds to a preparation as it is usually used for the application of bookbinding.

In a 2 L flat ground cup, the proportions of polyol specified in Table 1 are introduced, melted at 130 ° C and then dehydrated for 1 h at 130 ° C and 15 mbar (+/- 10 mbar) vacuum. The dehydrated polyol is then reacted with the appropriate amount of isocyanate. After about 20 minutes, the products are filled in aluminum cartridges and sealed airtight. The cartridges are then tempered for 4 h at 100 ° C in a convection oven. The result is a product having a viscosity of 5000 mPas (at 130 ° C), an NCO content of 2.24 wt .-% and a residual monomer content of 3.00 wt .-%. Table 1: Composition of Comparative Example 1 Isocyanate I-1 15.25% by weight Polyester A 32.50% by weight Polyester B 32.50% by weight Polyester C 16.20% by weight Polyether A 3.25% by weight Stabilizer A 0.30% by weight

Preparation of Inventive Example 1

The proportions of polyol indicated in Table 2 are introduced into a 2 L flat ground cup, melted at 130 ° C. and then dewatered at 130 ° C. and 15 mbar (+/- 10 mbar) under reduced pressure for 1 h. The dehydrated polyol is then reacted with the appropriate amount of isocyanate I-2. After about 20 minutes, isocyanate I-3 is added and homogenized for about 10 minutes. The product is then filled into aluminum cartridges and these are sealed airtight. The cartridges are then tempered for 4 h at 100 ° C in a convection oven. The result is a product having a viscosity of 3100 mPas (at 130 ° C), an NCO content of 2.26 wt .-% and a residual monomer content of <0.1 wt .-%.

The composition of Example 1 is equivalent to Comparative Example 1. Table 2: Composition of Example 1 Isocyanate I-2 13.91% by weight Isocyanate I-3 29.70% by weight Polyester A 18.09% by weight Polyester B 12.68% by weight Polyester C 25.37% by weight Stabilizer A 0.25% by weight

Methods used to characterize the reactive polyurethane hotmelts:

To determine the viscosity, the products, which are filled in aluminum cartridges, melted in a convection oven at about 125 ° C for about 30 minutes and then brought to the respective measurement temperature. The characterization of the viscoelastic properties of the reactive polyurethane hotmelts is carried out with the MCR 301 Rheometer from Anton Paar. The spindle / measuring cup system Z4 and CC27 was used. The viscosity was recorded as a function of the shear rate and evaluated by the Carreau-Yasuda algorithm.

The NCO content was after DIN EN 1242 certainly.

To determine the OZ, the hotmelt adhesive is brought to the temperature indicated in Tables 3 and 4 and, after complete melting, applied as a bead of adhesive. The time at which the bead is finished applied is considered the zero point of the time measurement. At regular intervals (from 5 seconds to 1 minute, depending on the OZ of the hot melt adhesive to be examined), successive paper strips are pressed onto the bead with light pressure. After cooling the bead to room temperature, the strips are torn from the substrate. The longest time at which the bond can only be broken under material fracture is considered to be OZ.

To determine the AZ, the hotmelt adhesive is heated to the temperature indicated in Tables 3 and 4 and, after complete melting, applied as a bead of adhesive. Immediately after the caterpillar application, a long piece of paper, cut in half at regular intervals, is pressed onto the bead with light pressure. This time is considered the zero point of the time measurement. At regular intervals, successive paper strips are removed from the bead. The time during which the bond can only be broken under material fracture is considered AZ.

The content of free monomeric diisocyanate was determined by gel permeation chromatography (GPC). The measurement was carried out at room temperature. The eluent used was THF, the flow rate was 1 ml / min and the injection volume was 50 μl. The separation columns used were GPC columns packed with 5 μm separation material having a porosity of 500 Å, as described, for example, by MZ-Analysentechnik, Mainz Description MZ-Gel SD-plus are available. The total length of the columns is 120 cm. The detector used was a refractive index detector. Results: Table 3: OZ and AZ of Comparative Example 1 and Inventive Example 1 hotmelt Comparative Example 1 example 1 application temperature 130 ° C 130 ° C 115 ° C 100 ° C OZ [s] 45 53 44 44 AZ [s] 22 35 40 28

It can be clearly seen that by lowering the application temperature of Example 1, the OZ and AZ can be reduced to the level of Comparative Example 1. For the user, this represents an advantage in terms of time expenditure, energy costs and workplace hygiene.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10163857 A [0012]
• EP 0693511 A [0013]

Cited non-patent literature

• Ullmanns Enzyklopadie der technischen Chemie, "Polyester", 4th edition, Verlag Chemie, Weinheim, 1980 [0039]
• Ullmanns Enzyklopadie der technischen Chemie, "Polyester", 4th edition, Verlag Chemie, Weinheim, 1980 [0040]
• Ullanns Enzyklopadie der technischen Chemie, "Polyester", 4th edition, Verlag Chemie, Weinheim, 1980 [0041]
• DIN EN 1242 [0052]

Claims (10)

Reactive polyurethane systems containing (a) NCO prepolymers based on asymmetric isocyanates or mixtures of asymmetric isocyanates and (b) prepolymers having a content of free monomeric isocyanate of <1 wt .-%. Process for the preparation of reactive polyurethane systems according to Claim 1, characterized in that (A) comprises at least one monomeric aromatic, aliphatic, araliphatic and / or cycloaliphatic diisocyanate whose isocyanate groups have different reactivities with respect to polyols or with a monomer having free NCO groups Diisocyanates constructed prepolymer and (B) a polyol or polyol mixture are reacted together, wherein the ratio of A to B is chosen so that the molar ratio of NCO to OH> 1. and then the reaction product of (A) and (B) is mixed with an isocyanate-terminated prepolymer having a content of free monomeric isocyanate of <1 wt .-%. Process according to Claim 2, characterized in that the isocyanate-terminated prepolymer used for blending with the reaction product of (A) and (B) has a content of free isocyanate of <0.5% by weight. Process according to Claim 2, characterized in that the isocyanate-terminated prepolymer used for blending with the reaction product of (A) and (B) has a content of free isocyanate of <0.1% by weight. Process according to Claims 2 to 4, characterized in that the diisocyanate component A) is isophorone diisocyanate and / or 2,4-diisocyanatotoluene and / or 2,4'-diisocyanatodiphenylmethane. Process according to Claims 2 to 4, characterized in that the diisocyanate component A) is 2,4'-diisocyanatodiphenylmethane. Preparations containing the reactive polyurethane systems according to claim 1. Hot melt adhesives (hotmelts) containing the reactive polyurethane systems according to claim 1. Use of reactive polyurethane systems according to claim 1 in sealants, coatings, foams, adhesives or hot melt adhesives. Use of asymmetric isocyanates or mixtures of these and reactive polyurethane systems containing such isocyanates or mixtures for reducing the application temperatures of hot melt adhesives.