FI75586B - SMAELTLIM. - Google Patents

Abstract

1. Adhesive fusible consisting of a composition comprising a prepolymer isocyanate, a lower molecular synthetic resin and optionally a thermoplastic polymer, characterized in that the composition comprises the following components : a) 20 to 90% by weight of prepolymer isocyanate, b) from about 0 to 75% by weight of a thermoplastic polyurethane consisting of diisocyanates, polyolen with a molecular weight of from about 1,000 to 3,000 and optionally shortbranched diolens with end-position primary or secondary OH-groups, whereby the quantity ratio of said components is selected such that the thermoplastic polyurethane practically does not contain any free OH- and NCO-groups and has a melting point of from about 70 to 170 degrees C, and c) further comprising from about 5 to 50% by weight of a lower molecular synthetic resin selected from the group containing ketone-aldehyde-condensation resins and/or hydration products of acetophenone condensation resins.

Description

1 75586

melt adhesive

The invention relates to a hot melt adhesive consisting of a mixture of an isocyanate prepolymer, a thermoplastic polymer and a low molecular weight synthetic resin.

Hot melt adhesives are already known. They consist of thermoplastic polymers, which are usually modified with artificial or natural resins, waxes, organic fillers, etc. They become fluid when heated o ...

100-200 ° C. Once the hot melt adhesive is applied to the substrate to be bonded, the adhesive cures rapidly and causes a solid adhesive bond.

The main advantage of hot melt adhesives over other adhesive systems is that bonding is rapid and that water and solvents are absent. An essential drawback is thermoplastic behavior. At high temperatures they become soft or flowable and at low temperatures they become hard and brittle, so that the adhesive bonds obtained in this way can only be loaded in a more or less narrow temperature range.

The same applies to previously known polyurethane hotmelt adhesives. They are expensive and do not offer similar advantages over conventional hotmelt adhesives based on ethylene vinyl acetate polymer polymers, polyamides and polyterephthalic acid esters. Polyurethane melts are highly viscous. Their stability at the required working temperature is poor. Initial strength and thermal strength are low. They adhere well to only a few materials.

Solvent-free, moisture-curable NCO prepolymers are still known. At room temperature, they are fluid or resemble soft wax. Due to their low initial strength and long reaction time, their use is limited.

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However, mixtures of these ingredients tend to be unfavorable or unstable in melting under certain mixing conditions. Their storage stability is often insufficient.

The object of the present invention is to overcome the disadvantages of the prior art and to provide durable, melt-stable and moisture-stable storage-stable hot-melt adhesives with good initial adhesion strength as well as high thermostability.

The object is achieved according to the invention by providing hot-melt adhesives consisting of a mixture of an isocyanate prepolymer, a thermoplastic polymer and in addition a low molecular weight synthetic resin, having the following composition: a) 20-90% by weight of isocyanate prepolymer and b) 0-75% by weight % of a polyurethane consisting of a thermoplastic diisocyanate, a polyol and a short-chain diol, and c) 5-50% by weight of a low molecular weight synthetic resin selected from ketone resins and / or ketone aldehyde condensation resins and / or hydrogenation products of acetophenone condensation resins.

In place of the thermoplastic polyurethane, the mixture may contain 10 to 70% by weight of a thermostable or stabilized thermoplastic polyester, preferably an ester based on terephthalic acid, dicarboxylic acids and diols and containing as few hydroxyl groups as possible. In this case, the hot-melt adhesive mixture no longer needs a low molecular weight synthetic resin.

When crystalline thermoplastic polyester is used instead of polyurethane, fast-setting hot-melt adhesives with a higher initial strength are obtained.

Il 3 75586 Such hotmelt adhesives are particularly well suited for gluing inorganic and organic substrates. But they are equally suitable for gluing thermosets and thermoplastics / foams, lacquered surfaces, wood and wood materials, paper, leather, imitation leather, rubber, textiles, fibrous materials and metals.

Not all polyesters are suitable for the hot melt adhesives of the invention. Polyesters which contain as few hydroxyl groups as possible are suitable. Polyesters, which contain more hydroxyl groups, give too viscous and even indigestible products and are therefore not suitable for hotmelt adhesives.

The invention also relates to hotmelt adhesives consisting of a mixture containing: a) 50-80% by weight of a prepolymer isocyanate, b) 0-2% by weight of a thermoplastic polyurethane or polyester, c) 20-70% by weight of a low molecular weight synthetic resin.

Due to their low viscosity, such adhesive formulations are suitable for spray application and are particularly well suited for gluing foams together or for gluing foams together with fibrous materials, textiles, imitation leather, leather, etc.

Manufacture of isocyanate prepolymers (A)

The reactive polyurethane prepolymers used in the adhesive according to the invention may contain: 1. aromatic diisocyanates, such as 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, or aliphatic or cycloaliphatic diisocyanates, such as e.g. -isocyanatohexane or diisocyanatoisophorone, or mixtures of these compounds or 4 75586 2. Prepolymers formed by the diisocyanates mentioned in point 1 with short-chain diols having terminal primary or secondary OH groups, e.g. 3. ranging from ethylene glycol to hexanediol-1,6 or from propylene glycol to hexapropylene glycol, or mixtures of these compounds, and branched polyesters with a molecular weight range between 1000 and 3000, or polycaprolactodiols having a molecular weight range of 1000 to 3000, and 4. short chain diols having terminal primary or secondary OH groups, as mentioned in 2.

The reactive polyurethane prepolymer used in the adhesive of the invention has a viscosity range of about 50 Pa.s to about 40,000 Pa.s, especially 500-40,000 Pa.s, at 20 ° C when the NCO content is about 1.0 to about 7.5, especially 2-5%.

Manufacturing is as follows:

Take the diisocyanate and / or diisocyanate prepolymer, heat it to 50-70 ° C, add the desired amount of the polyol component mentioned in A 3, then add the short chain diol mentioned in A 4 and keep the resulting mixture for 1-3 hours 80-120 ° C.

The proportions of the components are as follows: 1 mole of diisocyanate components 0.05 to 0.5 moles of polyol components 0.1 to 0.4 moles of short-chain diol components.

* Preparation Example 410 g of diisocyanate prepolymer based on 4,4'-di

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5,75586 to phenylmethane diisocyanate and tripropylene glycol (commercial product: Desmodur PF (Bayer AG)) are heated to 60 ° C and then 516 g of polyester diol based on adipic acid, ethylene glycol and butanediol are added with stirring. molecular weight of about 2000 and an OH number of about 55) and the mixture is heated to 90 [deg.] C. 74 g of tripropylene glycol are then added dropwise, taking care that the temperature does not rise above 110 [deg.] C. The mixture is stirred for 1.5 hours. ° C.

NCO: 2.7-3.2%.

Viscosity at 20 ° C 31,000 Pa.s (Brookfield HBT). Manufacture of thermoplastic polyurethanes (B)

The thermoplastic polyurethane used in the adhesive according to the invention consists of the following individual components.

1. Diisocyanates, such as, for example, 4,4'-diphenylmethane diisocyanate or 2,4-toluene diisocyanate or 2,6-toluene diisocyanate or isophorone diisocyanate or 1,6-diisocyanatohexane, or mixtures of these ingredients and 2. polyols, such as linear or slightly branched polyester diols with primary primary OH groups and a molecular weight between 1000 and 3000, or straight-chain or slightly branched polyethers with primary primary or secondary OH groups; groups with a molecular weight in the range of 1000-3000, or polycaprolactodiols with a molecular weight in the range of 1000-3000, and optionally 3. short-chain diols with terminal primary or secondary OH groups, such as, for example, those extending from ethylene glycol to hexanediol -1.6 or propylene glycol to hexapropylene glycol or diethylene glycol to hexaethylene glycol, or mixtures of these compounds.

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The thermoplastic polyurethane used in the adhesive according to the invention thus consists of one or more diisocyanate components mentioned in point 1, one or more polyol components mentioned in point 2 and optionally one or more further short-chain diols mentioned in point 3.

The proportions of said components may be as follows: B 1. 1 mole of diisocyanate B 2. 0.2 to 1.0 mole of long-chain diol B 3. 0.8 to 0.0 moles of short-chain diol, the proportions of components B 1 to B 3 is selected so that the thermoplastic polyurethane no longer contains virtually any OH and NCO groups.

Thermoplastic polyurethane (B) is a solid, rock hard substance with high cohesion at room temperature. Its melting point is between 70 and 170 ° C, in particular between 130 and 135 ° C. The composition of the polyol component of the thermoplastic polyurethane (B) should be similar to that of the prepolymer (A) in order to achieve the best possible compatibility with the prepolymer (A) over the entire temperature range (-30 to + 170 ° C). The thermoplastic urethane (B) must be free of NCO-reactive groups in the molecules in order to guarantee the storage stability of the hot melt.

Thermoplastic polyurethane (B) gives the hot melt adhesive mixture high strength at room temperature. In addition, the melting and softening point of the hot melt adhesive mixture according to the invention can be adjusted as desired by the amounts of thermoplastic urethane (B).

Depending on the amount, the surface of the hot melt adhesive mixture at room temperature is slightly sticky and rocky (Blockfest 3).

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Preparation Example of Thermoplastic Polyurethane 404.0 g of polyester diol based on adipic acid, butanediol-1,4 and ethylene glycol, having an OH number of about 55 and a molecular weight of about 2000 20.0 g of butanediol-1,4 109.5 g of 4,4'-isocyanatodiphenylmethane 533.5 g

The preparation is carried out as follows: 4,4'-diisocyanatodiphenylmethane is heated to 50-70 ° C, polyester diol is added, heated with stirring to 80 ° C and then butanediol-1,4 is added dropwise.

The mixture is stirred for 5 hours at 80 ° C. This forms a solid soft thermoplastic polyurethane with a melting point of 130 ° C.

A low molecular weight synthetic resin (C) is used to further modify the properties of the hot melt adhesive. Its softening point should be between 60-120 ° C. The resin must be compatible with both major components of the hot melt adhesive of the invention and must not react with the isocyanate groups of the prepolymer. Low molecular weight synthetic resins can be used to adjust properties * such as heat adhesion, initial strength, viscosity.

Preparation of small molecule resin (C) Small molecule resins are products prepared in the usual way from: a) aliphatic ketones such as acetone or methyl ethyl ketone, aliphatic aromatic ketones such as acetophenone, acetophenone, methylnaphthyl ketone, methylnaphthyl ketone , ethyl, tert-butyl and cyclohexylacetophenone, cycloaliphatic ketones such as cyclohexanone or methylcyclohexanone or a mixture thereof using as catalysts active neutral, basic or acidic condensing agents such as aldehydes, basic or acidic condensing agents and / or formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, crotonaldehyde or 3-oxybutyraldehyde in a molar ratio of ketonizaldehyde of 1: 1 to 2: 1.

The small molecule resin may also be c) a hydrogenation product of an acetophenone condensation resin.

The synthetic resins used according to the invention are described in: 1. H. Wagner, H.F. Sarx, Lack-Kunstharze (4th edition 1959), Karl Hanser Verlag, Munich, p. 79-83 2. Houben-Weyl Bd XIV, Teil 2, Georg Thieme Verlag, Stuttgart, 1963, pp. 416-424.

It is highly preferred to use a light, neutral, unsaponifiable ketone-aldehyde condensation resin. This resin has a density of about 1.19, an iodine color number of about 1.5, a acid number of about 0.1, and a softening point of about 79 ° C in a 50% toluene solution.

According to the above-mentioned literature reference 2, the synthetic resin can be prepared from acetophenone and formaldehyde in a molar ratio of 1: 1.

The hot melt adhesive according to the invention, consisting of the ingredients described above, is stable and storable for a long time (more than 8 months) and is solid at room temperature.

The application properties and bonding behavior are largely similar to those of ordinary hot melt adhesives. Initial strength is between satisfactory and good. As the reaction of the NCO groups with the humidity of the air proceeds, the bonding strength increases. The hot melt film, which is initially thermoplastic, becomes increasingly flexible and reaches an elastic end state.

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The reacted hot-melt adhesive films are non-meltable and their elasticity and strength are maintained over a wide temperature range. These, like adhesives, are resistant to greases, oils, plasticizers, and dilute acids and bases and are insoluble in most solvents and water. By varying the proportions of the prepolymer, thermoplastic polyurethane or polyester and the low molecular weight resin, the application and use properties can be modified in the required direction. The softening range (melting point), viscosity and application temperature of the hot melt depend on the molecular weight and quality of the isocyanate prepolymer (A) and the thermoplastic polyurethane (B) or polyester and the melting point of the low molecular weight synthetic resin (C).

The melt viscosity of the hot melt adhesive when measured on an Epprecht Rheomat 15 with Viskotemp is from about 0.1 to about 800 Pa.s.

The rate of crosslinking depends on the structure and quality of the isocyanate prepolymer (A) used.

The polyisocyanate prepolymer (A) should be the main component of the hot melt adhesive of the invention. It gives high flexibility to the finished reaction film, good cold and heat strength, good resistance to various substances such as solvents, grease, etc., and sufficient adhesion to several substrates.

If the proportion of the prepolymer (A) is less than 20% by weight, the properties of the thermoplastic polymer or synthetic resin begin to control. Cold and heat resistance are inferior. Responsibility for plasticizers, greases and solvents deteriorates. When the proportion of larger prepolymers (A) is more than 90%, the nature of the prepolymer is predominant. In this case, the initial strength of the unreacted adhesive mixture is very low and the surface of the film is not hard. According to the invention, it is preferred to use 50-75% by weight of part (A).

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Even very small amounts of thermoplastic polyurethane (B) or ester affect the rheological behavior of the prepolymer melts so that it is not completely absorbed into the porous substrates. The effect is already present in amounts of 2% by weight of component (B). An important property of the thermoplastic polyurethane (B) or polyester is that it is able to substantially increase the softening point and melting point of the adhesive mixture in amounts of the order of 5-10% by weight. The mixture of the prepolymer (A) between heavy-duty and soft-waxy becomes solid and the melt solidifies rapidly. The main requirement for a hot melt, i.e. that it binds rapidly when cooled, is thus achieved. As the amount (B) increases, the melt viscosity increases and at the same time the processing temperature and open time of the adhesive mixture shortens.

In adhesives which require high initial strengths and in which absorption into porous materials must be avoided, a thermoplastic polymer (B) of 2-75% by weight, preferably 5-55% by weight, is used.

If the technical requirements have a low melt viscosity in the foreground, the thermoplastic polyurethane (B) can either be omitted altogether or used in an amount of less than 2%.

The low molecular weight synthetic resin (C) improves both the heat adhesion and moisture absorption capacity and the bonding rate of the uncrosslinked adhesive mixture. In particular, it lowers the viscosity. Therefore, at least 5% by weight of resin (C) should be used. At an amount of more than 50% by weight, the use properties of the adhesive film, e.g. cold strength and resistance to grease, plasticizers and solvents, deteriorate, although cohesion and elasticity may still be sufficient. According to the invention, the preferred amount of component (C) is between about 5 and 40% by weight.

The adhesive composition according to the invention is storage stable when protected from light. Application takes place at 90 to 160 ° C

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11 75586 depending on the composition of the adhesive mixture and the temperature sensitivity of the substrate to be bonded.

If it is desired to glue plastic films, e.g. polyethylene films, it is expedient to use low viscosity controls and low melting points (Example 1, adhesive a), which can be properly applied at temperatures already between 90 and 100 ° C. Conventional thermoplastic hotmelt adhesives with sufficient thermal strength have substantially higher application temperatures and thus film damage may occur. Hot melt adhesives on the market with a lower application temperature have poorer thermal strength of the adhesive.

If it is desired to glue porous materials or in situations where gluing is immediately subjected to stress, highly viscous adjustments and higher softening and melting points are preferred (Example 2, adhesives b and c).

The hot melt adhesive can be applied with a scraper, roller or spray. Drum melters (Fasschmelzanlagen) are particularly preferred.

The hot melt adhesive according to the invention adheres to many organic and inorganic substrates, e.g. disposable and thermoplastics, including foams, various varnishes, rubber, textiles, fibrous materials, leather, wood, metal and paper.

The advantages of the crosslinked polyurethane hot melt adhesive are apparent from the following examples: 12,75586

Composition of adhesive mixtures in% by weight:

Examples according to the invention a__b_ c_d_ A Prepolymerized isocyanate-

ti according to Example 4 B Thermoplastic polyurethane according to Example 7 C Low molecular weight synthetic resin (commercially available 15 20 5 ketone aldehyde condensation product according to Example 7 D Polyester phthalic acid ester 55 Application example 1 Polyethylene film gluing

The pretreated LD-PE film1 (surface tension obtained by Corona pretreatment: 45 dynes / cm) was coated using a hot melt adhesive of 20 g / m 2. The hot melt adhesive a) has an application temperature of about 90 ° C; with a hot melt adhesive for plastics based on EVA resins, an application temperature of 120 ° C was required. Within 10 seconds, an equal film was placed on the adhesive-coated film and pressed. After 2 hours, test strips were cut to determine peel, heat, and cold strength. Table 1 compares the hot melt adhesive a) according to the invention with a special hot melt adhesive for plastics based on EVA resins.

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Low density polyethylene

table 1

Special hot melt adhesive for plastics according to the invention according to the invention (ISATHERM S 39/3)

Peeling strength of the adhesive: after 2 hours 1.1 pcs 1.8 pcs after 24 hours 1.8 pcs 1.9 pcs after 48 hours 2.5 pcs 1.9 pcs after 1 week Tear of the film 1.85 pcs 03 .2 kp) Thermal strength (4 years after 3 hours 24 hours) after 1 min at 50 ° C at 70 ° C 66 min 1/2 min

Adhesive mixture cold- Not at all Peeling strength at -10 ° C loss of adhesion at -20 ° C Not at wire Peeling loss of adhesion

measurement methods

To determine the peel strength, 15 mm wide test strips were peeled in a tearing machine.

Forward movement: 200 mm / min.

Thermal strength: 30 mm wide glued test strips were loaded with a weight of 300 g at the respective test temperature in a circulating air drying cabinet and the time during which the test strips weigh 60 mm was measured.

Cold strength was tested by hand, 30 mm wide, glued test strips were each kept for 1 hour in a freezer at low temperature and then loaded using strainers. It was examined whether the layers separated at the gluing of the test strip.

Cold cracking temperature: a 10 mm thick and 100 mm wide steel plate is placed vertically on the board on its narrow 14,75586 side. The 30 mm wide and 600 thick hot melt film is fixed with adhesive strips so that the film rests approximately half its width on the board. The other half of the hot-melt adhesive film is glued to the part of the steel plate perpendicular to the board. After 1 hour, the steel plate is poured so that the adhesive film folds. If the adhesive film does not break, lower the freezer temperature by 2 ° and repeat the procedure until the film breaks.

The viscosity of the hot melt adhesive was measured with an Epprecht Rheomat 15 plus Viskotemp instrument.

Application example 2 Bonding of rigid substrates (wood).

Adhesives b, c and d were compared to the adhesive for gluing the edges of furniture.

The test pieces, incubated with red beech, were prepared using the method WPS 68 for the determination of the thermal strength of hot melt adhesives for furniture.

The shear strength was determined according to DIN 53 254 and the thermal strength according to WPS 68.

Elongation at break and tensile strength were determined with 600 μm thick, 25 mm wide adhesive films using a tear machine. The fixing length of the film was 30 mm and the forward movement was 200 mm / min.

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Table 2

Pre-tunnel adhesive b) adhesive c) adhesive d) adhesive f) according to the invention, market-based hot-melt adhesive for furniture (Rakoll-Schmelzkleber___ 750_

Adhesive shear strength * 2 hours. 10kp / 4cm ^ 23kp / 4cmir 99kp / 4cm ^ 64 kp / 4 cm? 8 hours 38kp / 4cnC 203kp / 4cnj2 155kp / 4cm, 68 kp / 4 cm2 24 hours 207kp / 4cm ^ 213kp / 4 cm 202kp / 4cm 69 kp / 4 cm

Thermal strength of the adhesive according to WPS 68

2 hours 30-40 ° C 45-50 ° C 50-55 ° C 65-70 ° C

24 hours 170-175 ° C 180-185 ° C 160-165 ° C 65-70 ° C

48 hours 205-210 ° C 210-215 ° C 170-175 ° C 65-70 ° C

It can be seen from Tables 1 and 2 that the adhesive strength of the adhesive according to the invention, after complete crosslinking, is better than with conventional hot-melt adhesives both at room temperature and at high and low temperatures.

Table 3 summarizes the other physical properties.

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Table 3 a b c d e f

Plastic Furniture Melt Melt _ Glue Glue_

Viscosity 5 Pa.s 1000 Pa.s 2000 Pa.s 3000 Pa.s 14.0Pa.s 1600 Pa.s Order 0.2 Pa.s 9 Pa.s 160 Pa.s 900 Pa.s 4.5 Pa.s. s 490 Pa.s at 120 ° C at 150 ° C

Melting point

2 h after 67 ° C 90 ° C 92 ° C 115¾ 68 ° C 100 ° C

24 h after 110 ° C us1) us1) us1) 48 h after. us1) us1) us1) us1)

Fraction 420 4? 0 480% 52Q% 49Q% elongation

Breaking strength 13.6 kp 15.0 kp 17.4 kp 10.64 kp 1.4 kp 6.0 kp

Kylmässä-

broken <_35 ° c2) <_350c2) <-35 ° C2) -35 ° C -15 ° C -28 ° C

melt temperature 1) us = unmelted 2) Molten films could not be examined at temperatures below -35 ° C. The films of adhesives a, b and c are flexible at -35 ° C, but the films of EVA resin adhesives e and f are brittle.

The crosslinked hot melt adhesive films are highly resistant to solvents, oils, greases, plasticizers and dilute acids and bases.

Thus, PE films with 14-day-old adhesives made with adhesive b) were stored (storage time 5 weeks) in various solvents, and after 24 hours of ventilation, in which the solvent remaining in the adhesive joint was removed, the peel strength was measured on a tensile testing machine. The width of the test strips was 15 mm.

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The results obtained were as follows:

Solvent PE bonding peel strength after storage for 5 weeks in ___ listed solvents_ 3.2 kp / 15 mm film tearing Special gasoline 60/95 2.8 "

Toluene 3.2 "

Ethyl acetate 3.2 "film tearing

Acetone 2.9 ""

Trichlorethylene 3.1 "" PE adhesive release strength after 4 weeks storage in listed substances_

Dibutyl phthalate 2.8 kp / 15 mm film tearing

Dioctyl phthalate 2.9 ""

Aqueous sulfuric acid solution, 2n 3,2 ""

Aqueous nitric acid solution, 2n 2,2 ""

Potassium hydroxide 32 "” aqueous solution, 2n '

Water 2.8

Resistance to plasticizers

A soft PVC film with 30% DOP was glued with glue b and a plastic special glue d.

The glued strips were stored for 4 days at 50 ° C in an oven and, after cooling, the peel strength was measured at room temperature (test strip width 30 mm).

Samples glued with glue b got values of 2.8 pcs. Samples bonded with a special adhesive based on EVA resins peeled off. The glue became soft and slippery after absorbing the PVC plasticizer.

Claims (7)

A hot melt adhesive consisting of a blend containing an isocyanate prepolymer, a thermoplastic polymer and a low molecular weight synthetic resin, characterized in that the blend contains the following components: a) 20-90% by weight of the isocyanate prepolymer b) 0-75% by weight of a thermoplastic polyurethane based on a diisocyanate, a polyol and a short chain diol; c) 0-50% by weight of a low molecular weight synthetic resin from a group consisting of ketone resins and / or ketone aldehyde condensation resins and / or hydrogenated acetophenone condensation resins. 2. Adhesive adhesive according to claim 1, characterized in that the mixture contains 10-70% by weight of a thermoplastic polyester. 3. Adhesive adhesive according to claim 2, characterized in that the polyester is an ester based on terephthalic acid, dicarboxylic acids and diols and forms as little hydroxyl groups as possible. 4. Adhesive adhesive according to claim 1, characterized in that the mixture contains the following components: a) 50-80% by weight of the isocyanate prepolymer; b) 0-2% by weight of the thermoplastic polyurethane and c) 20-50% by weight of the layer molecular synthetic resin.