DE19742217A1 - Polyurethane for thermally removable label adhesive - Google Patents

Abstract

Hydrophilic, high molecular weight polyurethanes are obtained by reacting a di-isocyanate with a mixture containing hydrophilic and hydrophobic hydroxy compounds, e.g. polyethylene glycol and 1,10-decanediol, and preferably an ionic compound. Hydrophilic, high molecular weight polyurethane based on the reaction products of di-isocyanates with mixtures of hydrophilic and hydrophobic compound(s) containing hydroxyl (OH) groups, obtained by reacting 1-25 equivalents of di-isocyanate with 1-25 equivalents. OH group- containing component consisting of 1-5 equivalents diol(s), 0-5 equivalents triol(s) or tetra-ol(s) and 0-20 equivalents ionic compound(s), in which the hydrophilic hydroxy compound may be a polyethylene glycol (PEG) and/or a polypropylene glycol/PEG block copolymer with a mol. wt. of 1000-20,000. An Independent claim is also included for an adhesive composition containing this polyurethane.

Description

The present invention relates to a hydrophilic, high molecular weight polyurethane based on a reaction product of diisocyanates and hydroxyl groups compounds, an adhesive composition this Contains polyurethane, the use of this polyurethane as part of a Adhesive composition, in particular a hot melt adhesive or Solution / dispersion adhesive, for example a label adhesive and finally the use of this polyurethane as part of a Adhesive composition that after being on the back of a water absorbent substrate has been attached, which on a hard or Plastic surface was applied almost by heat treatment can be removed without residue from this surface.

For the labeling area of hard surfaces or plastic surfaces such as for example, glass and polyethylene terephthalate bottles are currently mainly glue based on casein. This watery Formulations are primarily based on one casein component and one Tackifier resin, in addition to certain additional additives. In this context For example, WO 93/03110 to name an adhesive based on Casein, water-soluble extenders, fillers and optionally others Additives describes where the adhesive is characteristic Contains resin acid derivatives and alcohol. This will make a flawless Labeling of moist glass bottles also possible at 15 ° C, even if  the casein content is well below the usual concentration of 18% by weight lies.

The above-mentioned labeling adhesives containing casein components, however, have the disadvantage that the removal of the labels when cleaning, in particular reusable bottles, is very complex. For example, in European patent application 503112 in column 1, line 36 to column 2, column 52, the following is stated:
"So far, the labels have been washed off with heated soapy water with a high water throughput. Handling the dirt load of the wastewater is correspondingly complex, which involves not only the required cellulose-fiber-free filtration of this wastewater, but in particular also the removal of metal components, in particular aluminum compounds the wastewater, which is present to a greater extent through the printing, that is to say the color components of the labels. The labels are detached in the bottle cleaning machine in an approximately 2.5% sodium hydroxide solution at an average temperature of 82 ° C. This detachment process takes place Of course, paper streak portions and thus also color and varnish portions from the printing into the lye. Labels thus burden the lye with dirt loads, which are assessed today according to the chemical oxygen demand (COD). The breweries in turn have to pay their waste water taxes according to the amount of Pay CSB. "

From the German patent application 31 37 324 is a bottle neck film known from a coated on both sides with a protective layer Section of aluminum foil, the protective layer consisting of a mixture of 1 to 40% alkali-resistant and 60 to 99% alkali-resistant binders consists. Polyvinyl acetate can be found there as alkali-resistant binder, Polyamide resins, melamine resins or cellulose nitrate application. The specified  alkali-resistant binders are state of the art Polyester resins from terephthalic acid and aliphatic diols, vinyl chloride Copolymers, polyvinyl butyral resins, acrylic resins and methacrylic resins or Mixtures of these. The alkali-resistant coating has the advantage that it detaches relatively easily from the bottle or the like, so that the actual washing process of the label either accelerates or with lower wash solution volumes can be carried out. The use of both alkali-resistant and alkali-resistant binders here only in order to keep the wash water too long Prevent downtimes of the system. Both belly labels as well As is well known, back and chest labels can have a high aluminum content contain. The neck foils consist mostly of Aluminum foil. The mostly multicolored printing of the labels used in increasing amount of gold or silver metal colored components, which makes increased accumulation of preferably aluminates in the cleaning solution mandatory surrender. The aluminate is an aluminum sludge that is found in the Washing machine is set down and disposed of. The hydrogen is made suctioned upwards from the cleaning machine. So that the aluminum dissolved 1.48 kg of sodium hydroxide is required per kilo of aluminum and especially the energy required for this. By suction of the About 25% of the energy is extracted with hydrogen. Through the alkali-resistant coating is attempted over the aluminum foil Keep alkali resistant and if possible the neck foil like a paper from the Discharge the lye again without the aluminum being dissolved in the lye Has.

In the European patent application 503112 is used to solve the problem proposed to mechanically remove the label from the return material in front of the Remove wet cleaning. This is made possible by the fact that between the Label and the previous adhesive layer a release layer is inserted.  

This enables peeling without tearing the label. The However, the adhesive layer remains on the bottles and must, as before, pass through Wash liquor can be removed. The problem of residue-free replacement of the Labels are therefore only partially solved.

In the German patent application 34 34 141 the previous adhesive (Glue) replaced by a mounting or fixing adhesive. This is said Have property not to harden, so that there is a label with this adhesive has been applied to a bottle, leaving no residue at any time can be removed. What the adhesive is made of is not disclosed.

However, it is disadvantageous that fixing adhesives require a dry substrate.

Automated Label Systems Company proposes "Auto sleeve "with the printing date 1993 for bottle labeling a polyethylene Banderole label that is pulled over the container in the expanded state and, after contracting, lies firmly over the container. So there is no glue used at all. The label comes with a High-pressure water jet - like a knife - cut through. Supposedly supposed to the container will not be damaged. In any case, it must Polyethylene label should be discarded.

WO 94/13726 relates to a hydrophilic, high molecular weight, nonionic Polyurethane, which is characterized by its water solubility and its specific viscosity of at least 0.4 as a 1% aqueous solution at 20 ° C. Such polyurethanes are essentially made of polyethylene glycol with a Molecular weight of 336 to 24,000 g / mol and a diisocyanate, preferably Tetramethylxylene diisocyanate without catalyst and without solvent at 80 to 200 ° C and can be used as the basis for an adhesive, especially one Hot melt adhesive or solution adhesive, for example for gluing wallpapers  and labels. The molar ratio of diol to diisocyanate is as close as possible to 1: 1 in order to achieve a high molecular weight.

Based on this state of the art, the task arises Adhesive composition in the form of a labeling adhesive both aqueous and also available as a hot melt, in addition to good ones application properties such as good adhesive strength Possibility to be removed thermally at about 50 to 70 ° C. With this, both the complex bottle cleaning and the Disposal of the wash liquor can be avoided, as was previously the case in the Technology was necessary.

The solution according to the invention is defined in the claims.

The present invention initially relates to a hydrophilic high molecular polyurethane based on reaction products from Diisocyanates and at least one hydrophilic and at least one hydrophobic, hydroxyl-containing compound, being a Reaction product of 1 to 25 equivalents of a diisocyanate and 1 to 25 Equivalents of a compound having hydroxyl groups, the Hydroxyl group-containing compound of at least 5 equivalents a diol, 0 to 5 equivalents of at least one triol or tetraol, 0 to 20 Contains equivalents of at least one ionic compound, the hydrophilic Compound containing hydroxyl groups is a polyethylene glycol and / or Polypropylene glycol / polyethylene glycol block copolymer with a molecular mass from 1000 to 20,000 g / mol. In particular, this has hydrophilic Compound having hydroxyl groups has a molecular mass of 3000 to 13,000 g / mol.  

This polyurethane preferably contains a reaction product of 1 to 25 Equivalents of a diisocyanate and 0 to 25 equivalents of a hydroxy Group-containing compound, the hydroxy group-containing Compound 1 to 5 equivalents of at least one diol, 1 to 5 equivalents at least one triol or tetraol and 1 to 20 equivalents of at least one contains ionic component.

The hydrophilic high molecular weight according to the invention preferably has Polyurethane has a melting point in the range from 50 ° C to 70 ° C.

In the hydrophilic high molecular weight polyurethanes according to the invention should the molar ratio of diol to diisocyanate is as close as possible to 1: 1, to achieve high molecular weight. The molar ratio is general 0.6-1: 1.1, preferably 0.7 to 1: 1.

The diol component is selected for the polyurethanes according to the invention from the hydrophilic diol polyethylene glycol and / or a polypropylene glycol / Po polyethylene glycol block copolymer with a molecular mass of 1000 to 20,000 g / mol, preferably with a molecular mass of 3000 to 14,000 g / mol as well Alkanediols with 2 to 44 carbon atoms, hereinafter hydrophobic diols called. This includes, for example, polytetrahydrofuran with one molecular weight from 400 to 3000, in particular 1000 to 2000 and 1,10-decanediol, 1,12-dodecanediol, 1,12-octadecanediol, dimer fatty acid diol, 1,2-octanediol, 1,2-Do decanediol, 1,2-hexadecanediol, 1,2-octadecanediol, 1,2-tetradecanediol, 2-Bu ten-1,4-diol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol. These are preferably hydro phobic diols alone or mixed in an amount of 0.0 to 10, in particular from 1 to 8 wt .-%, based on the total polyurethane used.  

In the case of the production of the hydrophilic high molecular weight polyurethanes The triplets and tetraols used are, for example, glycerol, Trimethylolethane (TME), trimethylolpropane (TMP) and pentaerythritol. Is preferred TMP.

As an ionic component in the hydrophilic high molecular weight polyurethanes an at least one anionic group, such as. B. carboxylate and / or Sulfonate groups and / or cationic groups such as e.g. B. quaternary Compound containing ammonium groups used. Is preferred Dimethylpropionic acid (DMPA).

In addition to these compounds containing hydroxyl groups are the diisocyanates essential building blocks of the polyurethane according to the invention. This is what it is about are compounds of the general structure O = C = N-X-N = C = O, where X is a aliphatic, alicyclic or aromatic radical, preferably a aliphatic or alicyclic radical with 4 to 18 carbon atoms.

Examples of suitable isocyanates are 1,5-naphthylene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), hydrogenated MDI (H ₁₂ MDI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), 4,4'-diphenyldimethyl methane diisocyanate, Di- and tetraalkyldiphenylmethane diisocyanate, 4,4-dibenzyl diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, the isomers of tolylene diisocyanate (TDI), 1-methyl-2,4-diisocyanato-cyclohexane, 1,6-diisocyanate nato -2,2,4-trimethylhexane, 1,6-diisocyanato-2,4,4-trimethylhexane, 1-isocyanato methyl-3-isocyanato-1,5,5-trimethylcyclohexane (IPDI), chlorinated and brominated diisocyanates, phosphorus-containing diisocyanates , 4,4'-diisocyanato-phenylperfluoret han, tetramethoxybutane-1,4-diisocyanate, butane-1,4-diisocyanate, hexane-1,6-dii socyanate (HTI) dicyclohexylmethane diisocyanate, cyclohexane-1,4-diisocyanate, ethylene diisocyanate, Bis-isocyanatoethyl phthalate, and also diisocyanates of reactive halogen atoms, such as 1-chloromethylphenyl-2 , 4-diisocyanate, 1-bromomethylphenyl-2,6-diisocyanate, 3,3-bis-chloromethyl ether-4,4-diphenyldiisocyanate. Sulfur-containing polyisocyanates are obtained, for example, by reacting two moles of hexamethylene diisocyanate with one mole of thiodiglycol or dihydroxy dihexyl sulfide. Other important diisocyanates are trimethylhexamethylene diisocyanate, 1,4-diisocyanatobutane, 1,12-diisocyanatododecane and dimer fatty acid diisocyanate. Particularly suitable are: tetramethylene, hexamethylene, undecane, dodecamethylene, 2,2,4-trimethylhexane, 1,3-cyclohexane, 1,4-cyclohexane, 1,3- or 1,4-tetramethylxylene -, Isophorone-, 4,4-dicyclohexylmethane, lysine ester dii socyanate and the 1-isocyanatomethyl-3-isocyanato-1,5,5-trimethylcyclohexane. It is very particularly preferred that 1-isocyanatomethyl-3-isocyanato-1,5,5-tri methylcyclohexane and tetramethylxylene diisocyanate, in particular the meta-TMXDI from Cytec.

The polyurethanes according to the invention can be used both in a single stage and can also be produced in a two-stage process. In the two-stage The process first produces a prepolymer in which a part of the Pre-react the compound containing hydroxyl groups with the diisocyanate. Then the further compound containing hydroxyl groups is added.

However, the polyurethane according to the invention is preferably used in one one-step process. First, all starting materials can be in Presence of an organic solvent with a water content of less are mixed as 0.5% by weight. The mixture is then at 80 ° C to 200 ° C, in particular 100 ° C to 175 ° C for about 1 to 30 hours, preferably 1 to 5 Heated for hours. The reaction time can preferably be determined by the presence of Catalysts can be shortened, for example with 0.02-0.5% (DBTL) and 0.02-0.5% (DABCO).  

To increase the storage stability, the finished polyurethane is also customary Additives and additives added, such as antioxidants as well Preservatives.

The polyurethanes according to the invention are in all proportions with water miscible and can therefore be part of adhesive compositions be used. Such an adhesive can be used both as a solution adhesive and also as a hot melt adhesive without a liquid component on the back of Water absorbing substrates are applied and in this respect a Effect connection on hard surfaces or plastic surfaces.

According to a further preferred embodiment, the present relates Invention the use of the aforementioned polyurethane as part of a Adhesive composition after application on a water absorbent surface, especially paper or labels and gluing a hard or plastic surface by heat treatment, in particular at 60 to 80 ° C is removed almost completely from the surface.

The invention is explained in more detail below by examples.

A (Preparation and properties of a water soluble high molecular weight Polyurethane) example 1

90.9 parts by weight (1 equivalent) of PEG 12 000 S (polyethylene glycol with a Molecular mass of 12,000; Hoechst AG) was melted at about 80 ° C and placed in a polyurethane hot melt system. Then this was Component and 4.4 parts by weight (2.06 equivalents) of 1,12-hydroxystearyl alcohol (Loxanol® from Henkel KGaA) at about 80 ° C for 2 hours in an oil pump vacuum,  d. H. at about 1 mbar, dewatered and then aerated with nitrogen. Thereupon 4.7 parts (2.9 equivalents) of m-TMXDI (commercial product from Cytec) added and the stirred kettle heated to 145 ° C. The course of the reaction was checked on the basis of the NCO content and the melt viscosity. After about The theoretical NCO content of 0% is reached for 3 hours. The Melt viscosity (according to Epprecht) is around 65,000 to 85,000 mPas 125 ° C.

Before filling, the polyurethane is given the usual antioxidants - here 0.1 part of Irganox® L 57 from Ciba Geigy AG - and a common one Preservative - here 0.1 part Kathon 886 F, available from Rohm & Haas GmbH - admitted. The stirring time itself is about 10 minutes. Out the nonionic polyurethane obtained in this way is given the corresponding adhesive according to the invention by first 64.5 parts by weight distilled water and 14 parts by weight of an aqueous balsam resin (Flexin® D) presented in a dispersion kettle. The high molecular weight obtained above Polyurethane is then in an amount of 21.5 parts by weight, initially in preheated in an oven, added to the reaction mixture. The Polyurethane is dissolved at about 70 to 80 ° C within 2 hours. In turn 0.1 part by weight of Irganox® before filling the adhesive formulations L 57 (antioxidant from Ciba Geigy AG) and 0.1 part Kathon 886 F (Preservative from Rohm & Haas GmbH) added. The stirring time was again about 10 minutes.

The solution thus obtained showed a Brookfield solution viscosity 25 ° C from 20,000 to 40,000 mPas.

B (Manufacture and properties of a polyurethane hot melt adhesive) Example 2

In a 2 l three-necked flask equipped with a stirrer and nitrogen feed, 561 g (0.2 Equivalents) Polyethylene glycol 6000 (Hüls AG), 112.16 g (1.67 equivalents) Dimethylolpropionic acid (Angus Chemie) and 26.7 g (0.164 equivalents) Loxanol® (Product of Henkel KGaA = 1,12-octadecanediol) 2 hours at 80 ° C and one mbar vacuum drained. It was then vented with nitrogen, 236.6 g (1.936 Equivalents) m-TMXDI (Cytec) added and the mixture homogenized. The The substance was then heated to 145 ° C. After 2 hours the NCO Ge was stop 0%. The polyurethane thus obtained showed one at 125 ° C Melt viscosity of 36 Pas. The application properties of this Polyurethane obtained were both qualitative and based on the tensile and Peel strengths depending on the temperature used following table determined.

The determination of the adhesive strength of paper to polyethylene terephthalate in the hydrophilic, high molecular weight polyurethanes according to the invention as a function the temperature was determined as follows:

First, an adhesive A according to Example 1 was applied in a manner known per se a paper label with a length of 10.5 cm and a width of 7.5 cm applied and as a wrapping label around a 1.5 l polyethylene terephthalate Soft drink bottle attached. From this series there were 5 labeled bottles manufactured. Thereupon was a previously calibrated drying cabinet for one hour set to the temperature defined below and then a labeled one Polyethylene terephthalate bottle added for 30 min. After that the drying cabinet was quickly opened and an attempt was made to remove the label with the result shown in the table below.  

Table 1

Adhesive strength paper / PET from adhesive A

The above table shows that up to about 55 ° C is sufficient Adhesion between paper and polyethylene is present and from about 63 to 64 ° C the label can be removed completely.

In the same way 6 1.5 liter polyethylene terephthalate soft drink bottles were used the adhesive B according to the invention connected to paper labels. The corresponding drying cabinet temperature and the separation or Non-separation of paper and polyethylene terephthalate is as follows Table 2. With this hot melt polyurethane adhesive, up to a temperature of 48 to 50 ° C no separation of the label from the bottle can be achieved, whereas at temperatures of 53 to 54 ° C the Label was easily separable from the bottle.  

Table 2

Adhesive strength paper / PET from adhesive B

Claims (11)

1. Hydrophilic high molecular weight polyurethane based on reaction products of diisocyanates and at least one hydrophilic and at least one hydrophobic hydroxyl compound, wherein it is a reaction product of
1 to 25 equivalents of a diisocyanate and
1 to 25 equivalents of a compound containing hydroxyl groups,
wherein the compound containing hydroxyl groups
1 to 5 equivalents of at least one diol,
0 to 5 equivalents of at least one triol or tetraol,
0 to 20 equivalents of at least one ionic compound can exist and the hydrophilic hydroxyl group-containing compound can be polyethylene glycol and / or a polypropylene glycol / polyethylene glycol block polymer with a molecular mass of 1000 to 20,000 g / mol. 2. Polyurethane according to claim 1, characterized in that the Reaction product 1 to 20 equivalents of at least one ionic Contains component. 3. Polyurethane according to claim 1 or 2, characterized in that it is a Has melting point in the range of 50 to 70 ° C. 4. Polyurethane according to the preceding claims, characterized in that it has a molar ratio NCO / OH of 0.61: 1.1, preferably 0.7 to 1: 1 having. 5. Polyurethane according to the preceding claims, characterized in that the hydrophobic diol is selected from 1,10-decanediol; 1,12-dodecanediol,  1,12-octadecanediol, 1,2-octanediol, 1,2-dodecanediol, 1,2-tetradecanediol, 1,2-hexadecanediol and 1,2-octadecanediol. 6. Polyurethane according to the preceding claims, characterized in that the triol or tetraol is selected from glycerol, trimethylolethane, Trimethylolpropane and pentaerythritol. 7. Polyurethane according to the preceding claims, characterized in that the ionic component is dimethylol propionic acid. 8. Polyurethane according to the preceding claims, characterized in that the diisocyanate is selected from 4,4'-diphenylmethane diisocyanate Isomers of tolylene diisocyanate, hexane-1,6-diisocyanate, 1-diisocyanatomethyl-3-isocyanato-1,5,5-trimethylcyclohexane, 1-isocyanatomethyl-3-1,0-cyanato-1,5,5-trimethylcyclohexane and the isomers of tetramethylxylene diisocyanate. 9. adhesive composition containing a polyurethane according to claims 1 to 8th. 10. Use of the polyurethane according to claims 1 to 8 as part of a Adhesive composition, in particular a hot melt adhesive or a solution adhesive, for example a labeling adhesive. 11. Use of the polyurethane according to claims 1 to 8 as part of a Adhesive composition that after application to a water absorbent surface, in particular from paper materials and adhesive on a hard or plastic surface by heat treatment, especially at 50 ° C to 70 ° C almost residue-free Surface is removable.