ES2698799B2 - PRESSURE SENSITIVE POLYURETHANE THERMOPLASTIC ADHESIVES (PSA) WITH CONTROLLED PEGAJOSITY IN A SHORT TEMPERATURE RANGE - Google Patents

Description

DESCRIPTION

PRESSURE SENSITIVE POLYURETHANE THERMOPLASTIC ADHESIVES (PSA)

WITH CONTROLLED PEGAJOSITY IN A SHORT TEMPERATURE RANGE

Field of the invention

The present invention is framed in the general field of adhesives and in particular, it relates to a pressure-sensitive adhesive of thermoplastic polyurethane, whose tackiness is controlled in a short temperature range.

BACKGROUND OF THE INVENTION

According to the definition of the Pressure Sensitive Tape Council glossary, a pressure sensitive adhesive (PSA) is the one with permanent stickiness, it is able to adhere to different substrates only exerting a light pressure (1-10 Pa) with the fingers for a few seconds (1-5 seconds) without the need for activation (heat, solvent or water), maintains the binding to the substrate over time and separates without leaving residues on the substrate.

For the bonding to take place, the adhesive must possess high molecular mobility and fluidity under a slight pressure so that a good contact with the substrate is created, and at the same time it must possess a high intermolecular cohesive force and a certain elasticity. This last requirement is necessary to dissipate the mechanical energy during the separation of the union.

Adhesive tapes were the first products that were manufactured with pressure sensitive adhesives and were first used in 1840. Later the first protective labels and films were made, which appeared in 1930 and 1940 respectively. Today, products based on PSAs are almost indispensable in everyday life and include packaging tapes, labels, sticky notes, automotive use, medical use, etc.

Pressure sensitive adhesives (PSAs) for medical use, whether for prolonged contact with the skin or reusable, are of special interest. Currently, the most common pressure sensitive adhesives are based on rubber, acrylic polymers or polysiloxanes. Because the skin has a heterogeneous surface and roughness, the PSA adhesive must be able to deform under light pressure and ensure the highest possible contact on the skin. During the joining phase, the PSA adhesive must behave viscously (as a liquid) and be able to wet the entire surface of the substrate, and It must also resist shear forces and easily detach by applying peeling efforts.

Acrylic PSAs can be designed so that they exhibit good tack and adhesion properties. PSAs derived from polysiloxanes can possess adequate tack when resins are added, but these resins can migrate to the surface of the PSA and can cause allergies and / or damage to the skin, so their use tends to disappear. The PSAs derived from polyisobutylene usually contain naphthenic oils that also tend to migrate to the surface generating loss of adhesion.

Compared to rubber or acrylic pressure sensitive adhesives (PSAs), polyurethane-based PSAs are more hydrophilic. In addition, they are biocompatible with the skin, so they are preferred in medical applications. The main problem presented by polyurethane PSAs is their low tackiness compared to that of acrylic PSAs.

It is important to mention that polyurethane adhesives do not have, by themselves, the characteristic properties of PSAs.

Polyurethane PSAs can be prepared in several ways:

1- Addition of rosin resins, cumarona-indene resins, hydrocarbon resins and polyterpene resins to polyurethanes [US 3925283; US 3718712]. The choice of resins is based on their acidity, ie milligrams of KOH per gram of resin, and must not exceed 10. In addition, they require the addition of a plasticizer to improve fluidity and decrease viscosity. However, these PSAs present migrations of the resin to the surface, increasing its adhesion to peeling with time, not being able to separate easily and without damaging the substrate to which it has been applied.

2- Use an isocyanate / polyol ratio (or NCO / OH ratio) of less than one unit [US 4087392;

US 3930102; US 5714543; US 5591820.] and add crosslinking agents [Y. Nakamura, S. Nakano, K. Ito, K. Imamura, S. Fujii, M. Sasaki, Y. Urahama. Adhesion properties of polyurethane pressure-sensitive adhesive. J Adh Sci Tech. 2013; 27: 263-277]. However, the stickiness of these polyurethane PSAs is insufficient.

3- Add mixtures in different amounts of monofunctional polyols (polyester, polyether) of different molecular weight and functionality (2 and 3) during the synthesis of polyurethanes [US 5227409; US 5102714]. However, the PSAs obtained have a very low degree of cross-linking, which facilitates the migration of low-level chains. molecular weight to the surface of the PSA, deteriorating the stability of the adhesion with time. Polyols with C = C unsaturations have also been used to prepare polyurethane PSAs [US 3879248; US 3743616; N. Akram, RS Gurney, M. Zuber, M. Ishaq, JL Keddie. Influence of polyol molecular weight and type on the tack and peel properties of waterborne polyurethane pressure-sensitive adhesives. Macromol. React. Eng. 2013; 7: 493-503], but possess high sensitivity to oxidation.

4- Add copolymers with typical characteristics of a PSA to polyurethanes [US 5910536]. These PSAs have a high tack but do not separate easily from the substrate, ie they have an excessively high peel strength.

In PSAs for medical use for contact with human skin is required not to irritate the skin or generate allergies and to bind to the skin quickly, maintaining its adherence over time to body temperature. In addition, after being removed should not leave residues on the skin or cause trauma or injury. In this sense, the US patent application US2012 / 121686 refers to a polyurethane adhesive for biological applications that is only active at a temperature of 37 ° C and a relative humidity of 100%.

US Pat. No. 6093270 discloses a thermoplastic polyurethane adhesive comprising, among other components, resins, pigments, and other additives, but these adhesives are applied to substrates such as paper and cardboard, textile or wood at room temperature.

In particular cases, such as labeling in food and pharmaceutical products that require refrigeration, the adhesive must maintain its union at low temperature.

There is thus a need to provide PSA adhesives of thermoplastic polyurethane having the viscoelastic properties that solve the problems described in the state of the art, that is to say that they present good tack in different short and controllable ranges of temperature, suitable for medical uses, packaging or labeled, among others.

BRIEF DESCRIPTION OF THE INVENTION

The present invention solves the problems described above since it refers to PSA adhesives based on polyurethane which have a good equilibrium tackiness, cohesion-cohesion, with the ability to modify their tackiness when the temperature varies, both for a small range of temperatures, especially in applications in contact with skin (it is intended that PSAs have good adhesion at 37 ° C and less or no stickiness at temperatures below 25 ° C), as in a somewhat wider range of temperatures for special applications in food or transport labeling of merchandise (null tack required at temperatures below -10 ° C and good tack at room temperature).

Thus, the present invention, in a first aspect, refers to a pressure sensitive polyurethane thermoplastic adhesive with controlled tack as a function of temperature (hereinafter, thermoplastic adhesive of the present invention), comprising:

- an isocyanate of general formula R (NCO) n, where n is at least 2,

- at least one polyol or polyol mixture,

where the NCO / OH ratio is greater than 1, the functionality is at least 2, the molecular weight of the polyol or polyols is between 400-5000 g / mol and where the tack is optimal in the selected temperature ranges of between 10 - 39 ° C, 5 - 20 ° C and -10 -5 ° C.

In a particular embodiment, the isocyanate of the PSA adhesive of the present invention is selected from aliphatic isocyanates, aromatic isocyanates derived from methylene diphenyl 4,4'-diisocyanate (MDI), isocyanates derived from 2,6-toluene diisocyanate (TDI), and isocyanate prepolymers.

In a particular embodiment, the polyol or polyol mixture of the PSA adhesive of the present invention is selected from polyether, polyester, polycaprolactone, polycarbonate diol and mixtures thereof.

In a particular embodiment, the polyols that are part of the polyol mixture can be of the same or of a different chemical nature.

In a particular embodiment, the NCO / OH ratio is comprised between 1.01-1.40.

In a particular embodiment, for an optimum tack in a temperature range comprised between 10-39 ° C, the polyol mixture of the PSA adhesive of the present invention, comprises polyols with molecular weight of 400 g / mol, 1000 g / mol and 2000 g / mol, the percentage of polyols of molecular weight 2000 g / mol being less than 50% of the total thereof, and the NCO / OH ratio is between 1.05-1.10. Preferably, the polyol mixture comprises poly (tetrahydrofuran) s and / or propylene glycols with molecular weight of 400 g / mol, 1000 g / mol and 2000 g / mol, the percentage of weight polyols being molecular weight 2000 g / mol less than 50% of the total. More preferably, the polyol mixture comprises polypropylene glycol and polycarbonate diol.

In another particular embodiment, for optimum tack in a temperature range comprised between 5-20 ° C, the polyol mixture of the PSA adhesive of the present invention, comprises polyols with molecular weights of 1000 g / mol and 2000 g / mol , and an NCO / OH ratio between 1.20-1.35. Preferably, the polyol mixture comprises a mixture of propylene glycol with molecular weight of 1000 g / mol and poly (tetrahydrofuran) with molecular weights of 1000 g / mol and 2000 g / mol.

In another more particular embodiment, for an optimal tack in a temperature range comprised between -10 - 5 ° C, the polyol mixture of the PSA adhesive of the present invention, comprises polyols with molecular weight of 2000 g / mol, and the NCO / OH ratio is between 1.30-1.40. More particularly, the polyol mixture comprises a mixture of polypropylene glycol and polyester polyol wherein the maximum amount of polyester polyol is 50% by total weight of the polyol mixture.

In a particular embodiment, the PSA adhesive of the present invention comprises a chain extender. More particularly, the chain extender is selected from diol or diamine, more preferably it is selected from 1,4-butanediol and alcohol amines such as ethanol amine.

In another aspect, the present invention relates to a support comprising the adhesive of the present invention.

In the present invention, "support" refers to any surface in or on which the adhesive of the present invention can be contained or incorporated.

In another aspect, the present invention relates to the use of the adhesive of the present invention in labels, prostheses, films, packaging tapes, pharmaceuticals.

In another aspect, the present invention relates to a process (hereinafter, method of the present invention) for the preparation of the PSA adhesive of the present invention, which comprises the following steps:

a) mixture of an isocyanate or mixtures of isocyanates, and a polyol or mixture of polyols,

b) catalyst addition,

c) evaluation of the free NCO in the reaction, until an NCO / OH ratio greater than 1 is achieved,

d) addition of chain extender until polyurethane is obtained.

In a particular embodiment, the isocyanate of step a) of the process of the present invention is selected from aliphatic isocyanates, aromatic isocyanates derived from methylene diphenyl 4,4'-diisocyanate (MDI), isocyanates derived from 2,6-toluene diisocyanate (TDI) and isocyanate prepolymers.

In a particular embodiment, the polyol or polyol mixture of step a) of the present invention is selected from polyether, polyester, polycaprolactone, polycarbonate diol and mixtures thereof.

In a particular embodiment, the NCO / OH ratio is comprised between 1.01-1.40.

In a particular embodiment, the catalyst of step b) of the process of the present invention is an organic catalyst selected from organic tin catalysts, tertiary amines, guanidines, cyclic amidines, W-heterocyclic carbenes and organic acids. More particularly, the catalyst is selected from tin dibutyl dilaurate (DBTL), dibutyltin diacetate (DBTDA), 1,4-diazabicyclo [2.2.2] octane (DABCO), 1,5,7-triazabicyclo [4.4 .10] dec-5-ene (TBC), W-methyl-1,5,7-triazabicyclododecene (MTBD), 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU); 1,3-bis (diterbutyl) imidazol-2-ylidene; trifluoroacetic acid (TFA), diphenyl phosphate (DPP) and triflioromethane sulfuric acid (MSA). Preferably, the catalyst used in step b) of the process of the present invention is selected from tin dibutyl dilaurate (DBTL) and dibutyl tin diacetate (DBTDA).

In a particular embodiment, the chain extender of step d) of the present invention is selected from diol or diamine. More particularly, the chain extender is selected from diol or diamine, more preferably it is selected from 1,4-butanediol and alcohol amines such as ethanol amine.

In a particular embodiment, the reaction time of step d) of the process of the present invention is 10 minutes.

Description of the figures

Figure 1 shows the variation of stickiness with the temperature of some polyurethane PSAs prepared with mixtures of polypropylene glycols of molecular weights 1000 and 2000 g / mol and NCO / OH ratio equal to 1.10.

Figure 2 shows the variation of stickiness at 25 and 37 ° C of polyurethane PSAs as a function of the weight percentage of poly (tetrahydrofuran) of molecular weight 1000 g / mol for PSAs prepared with mixtures of polypropylene glycol of molecular weight 2000 g / mol and poly (tetrahydrofuran) of molecular weight 1000 g / mol with an NCO / OH ratio equal to 1.20.

Figure 3 shows the viscoelasticity window of Chang at different temperatures of a polyurethane PSA prepared with a mixture of polypropylene glycol of molecular weight 2000 g / mol and 1,4-butanediol polyadipate of molecular weight 2000 g / mol with a ratio in weight 50/50 and an NCO / OH ratio equal to 1.30.

Figure 4 shows the variation of the tack with the temperature of PSAs of polyurethane prepared with mixtures of polypropylene glycol of molecular weight 2000 g / mol and polycarbonate of 1,6-hexanediol of molecular weight 2000 g / mol.

Detailed description of the invention

The invention relates to PSAs with intelligent properties so that their tackiness is controlled by the temperature in a narrow range of values, 20-39 ° C, 5-20 ° C and -10-5 ° C. By means of the use of different polyols or polyol mixtures and synthesis conditions new formulations of PSAs of thermoplastic polyurethanes are obtained.

The polyurethane PSAs were prepared by reaction of an isocyanate or mixture of isocyanates, with a polyol or mixture of polyols (polyether, polyester, polycaprolactone, polycarbonate diol) with molecular weights between 400 and 5000 g / mol.

Some isocyanates suitable for this invention are shown in Table 1. Preference is given to aromatic isocyanates derived from methylene diphenyl 4,4'-diisocyanate (MDI) with functionality 2, although isocyanates derived from 2,6-toluene diisocyanate (TDI) can also be used. ) or isocyanate prepolymers having a functionality greater than 2. In addition, hexamethylene diisocyanate, hydrogenated MDI, isophorone diisocyanate, L-lysine diisocyanate, etc. are also isocyanates suitable for this invention.

Table 1. Some isocyanates suitable for this invention.

Commercial name Composition NCO (%) Functionality Provider

Desmodur 44M 1-isocyanato-4 - [(4-33.6 2 Covestro Flakes phenylisocyanato) methyl] benzene,

2,4'-MDI content <1.8

Desmodur T80 2,4-diisocyanato-1-methyl- 48 2 Covestro benzene, content of 2,4-TDI = 67%

Desmodur T65N 2,4-diisocyanato-1-methyl-48 2 Covestro benzene, content of 2,4-TDI = 80%

Suprasec 5025 polymeric MDI 31 2.7 Huntsman

Some polyols suitable for this invention are shown in Table 2. Polyethers of functionality 2 and molecular weight equal to or greater than 2000 g / mol are preferred to impart adequate tack. A decrease in the molecular weight of the polyol promotes the cohesion of the polyurethane and the addition of polyols of higher functionality provides additional physical crosslinking to the polyurethane. On the other hand, short chain polyols, such as glycerol, can also be used in the case where an increase in crosslinking of the polyurethane is required.

Table 2. Some polyols suitable for this invention.

Trade name Composition Weight Functionality index Molecular supplier OH

(g / mol)

(mg

KOH / g)

Alcupol® D-4011 Reagent polypropylene glycol, 4000 28 2 Repsol contains ethylene oxide

Alcupol® D-2021 Non-reactive polypropylene glycol, 2000 56 2 Repsol does not contain ethylene oxide

Alcupol® D-1011 Non-reactive polypropylene glycol, 1000 110 2 Repsol does not contain ethylene oxide

Alcupol® D-0511 Non-reactive polypropylene glycol, 450 250 2 Repsol does not contain ethylene oxide

Alcupol® X-1950 Trifunctional polyether 886 190 3 Repsol

Alcupol® X-1550 Trifunctional polyether 1032 163 3 Repsol

Alcupol® F-5611 Trifunctional Polyether 3000 56 3 Repsol

Alcupol® F-3531 Trifunctional polyether 4800 35 3 Repsol

Alcupol® F-2831 Trifunctional polyether 6000 28 3 Repsol

PTMEG2000 Poly (tetrahydrofuran) 2000 - 2 Sigma Aldrich

PTMEG1000 Poly (tetrahydrofuran) 1000 - 2 Sigma Aldrich

Hoopol® F501 1,4-butanediol polyadipate 2000 54-58 2 Synthesia

Hoopol® S105-55 Polyadipate 1.6- 2000 53-58 2 Synthesia hexanediol

Hoopol® F620 Neopentyl polyadipate 1000 107-117 2 Synthesia glycol

Hoopol® F600 Neopentyl Polyadipate 2000 54-58 2 Synthesia glycol

Eternacoll® UHC Copolymer of 1000 110 2 UBE 50-100 polycaprolactone and

1,6-hexanediol polycarbonate, 50/50

Eternacoll® UHC Copolymer of 2000 58 2 UBE 50-200 polycaprolactone and

1,6-hexanediol polycarbonate, 50/50

Eternacoll® PHA Copolymer of 2000 56 2 UBE 50-200 polycaprolactone and

1,5-pentanediol polycarbonate, 50/50

Eternacoll® UH Polycarbonate 1.6- 2000 56 2 UBE 200 hexanediol

Eternacoll® UG Polycarbonate diethylene diol 2000 56 2 UBE 200 glycol

The polyurethane PSA was prepared with an NCO / OH ratio between 1.05 and 1.40, preferably between 1.10-1.20 with excess isocyanate, using a diol or a small molecular weight diamine as a chain extender, preferably 1,4-butanediol, or alcohol amines, such as ethanol amine.

The reaction was carried out in the presence of an organic tin catalyst such as, for example, tin dibutyl dilaurate (DBTL) or dibutyltin diacetate (DBTDA). Other catalysts useful for this invention are tertiary amines such as 1,4-diazabicyclo [2.2.2] octane (DABCO); cyclic guanidines and amidines such as 1,5,7-triazabicyclo [4.4.10] dec-5-ene (TBC), W-methyl-1,5,7-triazabicyclododecene (MTBD), 1,8-diazabicyclo [5.4.0 ] undec-7-ene (DBU); W-heterocyclic carbenes such as 1,3-bis (diterbutyl) imidazol-2-ylidene, etc; organic acids such as trifluoroacetic acid (TFA), diphenyl phosphate (DPP), trifluoromethane sulfuric acid (MSA), etc.

The polyurethane PSAs were prepared in a 500 mL four-drop reactor, equipped with a temperature controller, inert nitrogen atmosphere, and stirring rod with a Heidolf RZR-2000 agitation system (Kelheim, Germany). The polymerization reaction was carried out in two stages. A first step in which the appropriate amount of polyol (polyether, polyester, polycaprolactone, polycarbonate diol, or mixtures thereof) was reacted with diisocyanate, at 80 ° C under a nitrogen atmosphere for two hours, with an agitation of 250 rpm. After 90 minutes, the catalyst was added reducing the agitation at 80 rpm. Before adding the chain extender, the amount of free NCO in the prepolymer was determined by back-titration with dibutylamine (ASTM D5155). Next, the corresponding equivalents of chain extender were added to the prepolymer so that no NCO remained unreacted, maintaining the reaction for 10 minutes.

Some examples of formulations of polyurethane PSAs suitable for this invention are shown in Tables 3 to 6.

For applications with a notable variation of stickiness in a short temperature range (10-39 ° C), PSAs were prepared with an NCO / OH ratio of 1.10, and mixtures of polypropylene glycols of molecular weights 400, 1000 or 2000 g / mol and with functionality 2, preferably mixtures with less than 50% by weight of polypropylene glycol of molecular weight 2000 g / mol. Especially for medical applications, the synthesis of PSAs was carried out with mixtures of MDI and polycarbonate diol, preferably copolymer of 1,6-hexanediol caprolactone and polycarbonate of molecular weight 2000 g / mol and an NCO / OH ratio of 1.05.

Table 3 Compositions of polyurethane PSAs prepared with mixtures of polypropylene glycols of different molecular weights.

Polyol (g) a, b Diisocyanate (g) NCO / OH D-2021 D-1011 D-0511 X-1950 MDI

68.6 0 0 14.4 9.9 1.10

70 0 0 0 9.6 1.10

52.5 17.5 0 0 12.0 1.10

35 35 0 0 14.4 1.10

17.5 52.5 0 0 16.8 1.10

0 70 0 0 19.2 1.10

52.5 0 17.5 0 17.9 1.10

35 0 35 0 26.2 1.10

17.5 0 52.5 0 34.5 1.10

a In all cases, 0.04 mmoles of DBTL catalyst and the necessary amount of 1,4-butanediol as chain extender were added.

b The calculations have been made fixing the total polyol mass in 70 g.

Table 4 Compositions of polyurethane PSAs prepared with mixtures of polypropylene glycol and poly (tetrahydrofuran) s with different molecular weights.

Polyol (g) a, b Diisocyanate (g)

D-2021 PTMEG2000 PTMEG1000 MDI NCO / OH

35 35 0 9.2 1.05

35 35 0 9.6 1.10

35 35 0 10.5 1.20

35 35 0 11.8 1.35

17.5 26.25 26.25 12.6 1.05

17.5 26.25 26.25 16.2 1.35

52.3 8.75 8.75 10.3 1.05

52.3 8.75 8.75 13.3 1.35

24.5 22.75 22.75 12.8 1.10

24.5 22.75 22.75 16.20 1.40

35 17.5 17.5 12.0 1.10

35 17.5 17.5 13.1 1.20

0 70 0 9.2 1.20

52.5 0 17.5 13.1 1.20

50 0 50 15.7 1.20

17.5 0 52.5 18.4 1.20

0 0 70 21.0 1.20

a In all cases 0.04 mimetic DBTL catalyst and the necessary amount of 1,4-butanediol as chain extender were added.

b The calculations have been made fixing the total polyol mass in 70 g.

Table 5 Compositions of polyurethane PSAs prepared with mixtures of polypropylene glycol and polyester polyol of different molecular weights.

Polyol 3 'b Diisocyanate

D-2021 F501 MDI NCO / OH

70 0 11.40 1.30

75 25 11.40 1.30

50 50 11.40 1.30

a In all cases, 0.04 mmoles of DBTL catalyst and the necessary amount of 1,4-butanediol as chain extender were added.

b The calculations have been made fixing the total polyol mass in 70 g.

Table 6 Compositions of polyurethane PSAs prepared with mixtures of polypropylene glycol and polycarbonate diol.

Poliola, b Diisocyanate

D-2021 UH200 UG200 UHC-50-200 MDI NCO / OH

0 0 70 0 9.2 1.05

0 0 0 70 9.2 1.05

52.5 17.5 0 0 11.4 1.30

35 35 0 0 11.4 1.30

35 35 0 0 9.9 1.13

17.3 52.5 0 0 11.4 1.30

17.3 52.5 0 0 11.4 1.13

a In all cases, the appropriate amount of 1,4-butanediol was added as a chain extender and 0.04 mmoles of DBTL as a catalyst.

b ^{The calculations have been made fixing the total polyol mass in 70 g.}

For applications with good tack and cohesion at room temperature (5-20 ° C), PSAs were prepared with an NCO / OH ratio of 1.05-1.35 and with mixtures of polypropylene glycol of molecular weight 2000 g / mol and poly (tetrahydrofuran) s molecular 1000 or 2000 g / mol. More specifically, for applications with PSAs with a permanent bond and greater adherence, ternary polyether mixtures and NCO / OH ratios between 1.20 and 1.40 were used.

For PSAs in feed with stickiness and adhesion at low temperature (temperatures below 5 ° C), formulations based on blends of polypropylene glycol of molecular weight greater than 2000 g / mol and polyester polyol of molecular weight 2000 g / mol were used with amounts of polyester less than 50% by weight and an NCO / OH ratio of 1.30.

To obtain the PSA film on a polymeric carrier or carrier, as is well known to one skilled in the art, several methods can be employed. In order to prepare PSA films of thickness less than 50 microns, it is preferable to dissolve the adhesive in methyl ethyl ketone and to extend the solution by means of a grammage rod. For thicknesses greater than 50 microns the appropriate amount of adhesive is pressed in a hot plate press at 100 ° C applying a pressure of 3-4 kg / m2. In the present invention, the film thickness of Recommended PSA adhesive was in the range of 10 to 150 microns, preferably between 20 and 60 microns.

Next, a brief description of the characterization methods employed in this invention is made.

The rheological properties of the PSAs were determined in a Discovery Hybrid DHR2 rheometer (TA Instruments, New Castle, DE, USA), using parallel plates (diameter of the upper plate = 20 mm); the distance between plates was 0.4 mm. In the region of linear viscoelasticity, frequency sweep tests were carried out at 25 ° C using an amplitude of 2.5% in the angular frequency range of 0.01 to 100 rad / s. The obtained values of elastic modulus (G ') and viscous modulus (G ") at frequencies 0.1 and 100 rad / s and at different temperatures are used to obtain the viscoelastic windows of Chu [S.-G. Chu. Dynamic mechanical properties of pressure-sensitive adhesives. In: L.-H. Lee (Ed.), Dynamic mechanical properties of pressure-sensitive adhesives. Adhesive Bonding. Plenum Press, New York, pp. 97-137] that are used to estimate whether an adhesive meets the requirements so that it can be used as a PSA. For this, the value of G 'at a frequency of 0.1 rad / s must be between 2-4104 Pa, and in addition it must be fulfilled that 5 <G' (ra = 100 rad / s) / G '(ra = 0.1 rad / s) <300.

The stickiness measurements of the PSAs were carried out by means of the "probe tack" test in a Texture Analyzer TA.XT2i (Stable Micro Systems, Surrey, England), which has a thermostatted chamber equipped with a Viscotherm VT10 thermostatted bath ( Physica, Zurich, Switzerland), which has been developed in the Adhesive and Adhesives laboratory of the University of Alicante. The stickiness of the PSAs was evaluated between 10 and 37 ° C (skin temperature). The PSA films were deposited on a stainless steel sheet with a thickness of 50-80 ^ m. A cylindrical stainless steel rod of 3 mm diameter (smooth contact surface) was used, using the following experimental conditions:

- Speed of approach of the stem to the sample: 0.1 mm / s

- Force applied to the sample: 5 N

- Contact time of the stem with the sample: 1 second

- Speed of separation of the stem of the sample: 10 mm / s.

The obtained values are the arithmetic mean of at least 5 replicas.

The peel adhesion measurements at 180 ° were evaluated in 5754 aluminum / adhesive / PET film (polyethylene terephthalate) joints. The dimensions of the aluminum specimens 5754 were 3 cm x 15 cm and those of the PET film were 3 cm x 18 cm. The area in which the PSA was applied was 21 cm2 (3 cm wide and 7 cm long), leaving 11 cm of PET film without adhesive to be able to hold it in the jaws of the test equipment. The 5754 aluminum specimens were cleaned with MEK (ethyl methyl ketone) before applying the adhesive, to remove contaminants.

The preparation of the adhesive joints was carried out by applying a thickness of 50-100. ^ M PSA on the aluminum specimen 5754. Then the PET film specimen was placed on top of the adhesive and pressed 30 times over a manual roller of 2 kg. The peel adhesion at 180 ° was obtained in an Instron 4411 universal testing machine (Instron Ltd., Buckinghamshire, England) using a peeling speed of 152 mm / min. The obtained values are the arithmetic mean of 5 replicas and are expressed in N / cm.

Examples

The following are some examples that show the invention and provide additional illustrations for the selection of the components, amounts and properties to obtain the polyurethane PSAs with controlled tack in a short temperature range (10-39 ° C, 5-20. ° C and -10 - 5 ° C).

Example 1

A polyurethane PSA was prepared by reaction of MDI with functionality 2 and a mixture of di- and tri-functional polyols (D2012 and X-1950) in proportions 98% and 2% respectively, with an NCO / OH ratio equal to 1.10. The values of tackiness, peel adhesion at 180 ° and the rheological properties at 25 ° C were measured. The results obtained are shown in Table 7. The stickiness values at 25 and 37 ° C were similar (566-617 kPa), the peeling force at 180 ° was 5.4 N / cm at 25 ° C being the type of failure produced adhesion failure. The addition of the trifunctional polyol (X-1950) did not change the stickiness of the adhesive between 25 and 37 ° C. The values obtained in plate-dish rheology showed that the Chu criteria were met, since G 'at 0.1 rad / s was 1.8104Pa and G' (ra = 100 rad / s) / G '(ra = 0.1 rad / s ) was 15.5.

Table 7

Stickiness Stickiness Force of G (104 Pa) G (ra-100 G (104 pa) at 25 ° C at 37 ° C pe ra oa = 0.1 ra = 100 rad / sec) / G 'ra = 0.1 «-100 ( kPa) (kPa) 180 ° (N / cm) rad / s rad / s (ro-01 rad / s) rad / s rad / s

617 ± 27 566 ± 66 5.4 ± 0.19 1.8 28.0 15.5 1.6 10.9

Examples 2-6

Polyurethane PSAs were prepared by reaction of MDI with mixtures of polypropylene glycols of molecular weights 1000 and 2000 g / mol. The tack was measured at different temperatures and the peel strength at 180 ° at 25 ° C. The values in Table 8 showed that a decrease in the weight percentage of polypropylene glycol of molecular weight 2000 g / mol favored the stickiness at 37 ° C and the stickiness at 10 ° C decreased considerably. All the formulations had a peeling force at 180 ° suitable for use as PSAs (2.4-11.2 N / cm), the type of failure observed being the cohesion of the adhesive in Examples 2-5 and adhesion failure in Example 6 .

Table 8

No D2021 (% D1011 N CO / OH Stickiness to Stickiness Strength in weight) (% at 10 ° C (kPa) at 37 ° C peeled at 180 ° weight) (kPa) (N / cm)

2 100 0 1.10 880 ± 55 708 ± 8 4.1 ± 0.2

3 75 25 1.10 812 ± 11 933 ± 62 3.6 ± 0.2

4 50 50 1.10 420 ± 52 913 ± 71 3.4 ± 0.1

5 25 75 1.10 10 ± 1 272 ± 14 11.2 ± 0.9

6 0 100 1.10 3 ± 1 0.23 ± 0.01 2.4 ± 0.5 Table 9

The viscoelastic properties of polyurethane PSAs were also evaluated. The results measured at 25 ° C are shown in Table 9. The G 'values at 0.1 rad / s were found in a wider range than the high tackiness polysiloxane PSAs (0.5 4104 Pa) and within the range proposed by Chu (2-4104 Pa). The ratio G '(or = 100 rad / s) / G "(or = 0.1 rad / s) increased with the increase in the percentage of polypropylene glycol of molecular weight 2000 g / mol, which was related to an adequate peeling strength to 180 °.

Examples 7-9

Polyurethane PSAs were prepared by reaction of MDI with blends of polypropylene glycols of molecular weights between 450 and 2000 g / mol. The formulations of Examples 7-9 showed good tack at 37 ° C, decreasing considerably to 25 ° C (Table 10). The peel force values at 180 ° were suitable for PSAs (0.1-5 N / cm), with a failure of the adhesive cohesion for Example 7 and an adhesion failure in Examples 8 and 9. A decrease in the Peel strength at 180 ° when increasing the percentage of polypropylene glycol of molecular weight 450 g / mol. Table 11 shows the values of G 'and G "at 0.1 and 100 rad / s of the formulations of Examples 7-9. Higher values of G 'at 0.1 and 100 rad / s with respect to G "indicated an increase in the cohesion of the adhesive with respect to the PSAs of Examples 2-6.

Table 10

No D2021 D0511 NCO / OH Stickiness to Stickness to Force (% in (% by weight) 25 ° C (kPa) 37 ° C (kPa) peeled to weight) 180 ° (N / cm)

7 75 25 1.10 328 ± 10 456 ± 71 4.4 ± 0.2

8 50 50 1.10 298 ± 4 535 ± 6 1.0 ± 0.4

9 25 75 1.10 35 ± 0 121 ± 0 0.2 ± 0.02

Table 11

No D2021 D0511 G '(104 Pa) G' (or = 100 G '' (104 Pa)

(% by weight) (% at or = 0.1 or = 100 iad / s) / G (ra = °. ra = 0.1 or = 100 weight) rad / s rad / s 1 rad / s) rad / s rad / s

7 75 25 0.9 53.5 59 2.3 21.1

8 50 50 27.6 89.9 3 13.2 34.8

9 25 75 36.6 269.6 7 20.3 333.7

Examples 10-13

The PSA formulations described in Table 12 were prepared, using MDI as a diisocyanate and mixtures of polypropylene glycol and poly (tetrahydrofuran) of molecular weights of 2000 g / mol, functionality 2 and different NCO / OH ratios. For NCO / OH values lower than 1.10 a greater variation of the stickiness was observed with the temperature, while for higher NCO / OH values, the tackiness did not vary in the temperature range between 25 and 37 ° C (Table 12) . The peeling force at 180 ° measured at 25 ° C increased for NCO / OH ratios between 1.10 and 1.20 and the type of failure observed was cohesion of the adhesive in all cases. The viscoelastic properties are shown in Table 13. It is verified that they meet the criteria of Chu, except in example 13.

Table 12

No D2021 PTMEG2000 N C O / OH Stickiness to Stickiness to Strength (% in (% by weight) 25 ° C (kPa) 37 ° C (kPa) peeled by weight) 180 ° (N / cm)

10 50 50 1.05 278 ± 17 405 ± 22 0.6 ± 0.03

11 50 50 1.10 874 ± 18 760 ± 119 9.3 ± 0.4

12 50 50 1.20 576 ± 17 653 ± 23 9.9 ± 0.6

13 50 50 1.35 185 ± 8 174 ± 10 1.8 ± 0.04

Table 13

No G '(104 Pa) G (© = 100 G' '' (104 Pa)

© = 0.1 rad / s © = 100 rad / s ^{rad / s) / G (© = 0.1} © = 0.1 rad / s © = 100 rad / s rad / s)

10 0.81 44.3 55 1.9 14.1

11 0.64 58.1 91 1.7 23.5

12 0.77 59.6 77 1.9 21.8

13 0.03 28.8 960 0.3 19.5

Examples 14-17

PSAs were prepared using MDI and ternary mixtures of functional polyols 2 with different chemical nature and different molecular weights. The different formulations were prepared by varying the percentage of polypropylene glycol (25% and 75%) of molecular weight 2000 g / mol and with mixtures 50:50 by weight of PTMEG2000 and PTMEG1000 with NCO / OH ratios of 1.05 and 1.35. For NCO / OH ratios close to the unit and low polypropylene glycol contents (25%) a considerable variation of the tack between 37 and 25 ° C was achieved, with a good peeling force at 180 °. The type of failure observed was of adhesive cohesion in the case of examples 14 and 16 with an NCO / OH ratio equal to 1.05, while the use of higher NCO / OH ratios (1.35) resulted in adhesion failure (Table 14) . For higher amounts of polypropylene glycol and higher NCO / OH ratios, the stickiness was maintained between 25 and 37 ° C, giving values of peel strength suitable for PSAs. Values obtained from plate-dish rheology showed G 'values at 0.1 rad / s lower than the range proposed by Chu (2-4.104 Pa). One of the Chu criteria was not met in Examples 16 and 17 in which the 75% by weight percentage of propylene glycol was increased.

Table 14

No D2021 (% in PTMEG2000 / P NCO / OH Stickiness to Stickiness to Force of weight) TMEG1000 (% 25 ° C (kPa) 37 ° C (kPa) peeled to weight) 180 °

(N / cm)

14 25 75 1.05 466 ± 19 771 ± 17 2.8 ± 0.4

15 25 75 1.35 144 ± 7 244 ± 16 6.4 ± 1.4

16 75 25 1.05 694 ± 19 540 ± 19 1.3 ± 0.1

17 75 25 1.35 141 ± 8 293 ± 14 11.0 ± 1.2

Table 15

No G '(104 Pa) G' (© = 100 G '' (104 Pa)

ra = 0.1 rad / s ra = 100 rad / s rad / s) / G '(© = 0.1 ra = 0.1 rad / s ra = 100 rad / s rad / s)

14 0.2 42.6 213 0.9 20.6

15 14.1 103.0 7 12.4 25.0

16 0.03 27.2 907 0.3 16.2

17 1.4 70.8 501 3.2 21.9

Examples 18-21

PSAs were prepared using MDI and ternary mixtures of functional polyols 2 with different chemical nature and different molecular weights. The different formulations were prepared by varying the percentage of polypropylene glycol (35 and 50%) of molecular weight 2000 g / mol and with 50:50 by weight mixtures of PTMEG2000 and PTMEG1000 with NCO / OH ratios of 1.10 and 1.40. The use of mixtures of propylene glycols of molecular weight 2000 g / mol and PTMEG mixtures of molecular weights of 1000 and 2000 g / mol in percentages between 35-50% and 50-65% respectively, considerably increased the peeling strength at 180 ° keeping a good stickiness at 25 and 37 ° C (Table 16). The type of failure observed was adhesion failure in formulations prepared with 35% by weight of polypropylene glycol and adhesive cohesion for formulations with 50% by weight of polypropylene glycol. The values of G 'at low frequencies corresponded to formulations of PSAs with good tackiness while the values of G' (ra = 100 rad / s) / G '(ra = 0.1 rad / s) were below the limit.

Table 16

No D2021 (% in PTMEG2000 / P NCO / OH Stickiness to Stickiness to Weight Force) TMEG1000 (% 25 ° C (kPa) 37 ° C (kPa) peeled to weight) 180 ° (N / cm)

18 35 65 1.10 390 ± 23 476 ± 26 18.1 ± 4

19 35 65 1.40 299 ± 39 305 ± 48 21.1 ± 4

20 50 50 1.10 454 ± 57 633 ± 71 7.3 ± 1

21 50 50 1.20 257 ± 29 363 ± 33 5.8 ± 0.3

Table 17

No G '(104 Pa) G' (ffl = 100 G '' (104 Pa)

ra = 0.1 rad / s ra = 100 rad / s rad / s) / G (ra = 0.- | ra = 0.1 rad / s or = 100 rad / s rad / s)

18 8.9 10.6 1.2 98.3 17.9

19 10.5 10.0 0.95 99.1 21.0

20 2.6 4.8 1.9 78.7 21.0

21 0.5 1.5 3.2 55.2 23.2 Example 22

Polyurethane PSA adhesives for medical applications. PSAs were prepared from MDI and polycarbonate diol with an NCO / OH ratio of 1.05. The values shown in Table 18 indicated good tack at 37 ° C which decreased considerably at 10 ° C, also obtaining an excellent peeling force at 180 ° measured at 25 ° C, showing a failure of the adhesive cohesion.

Table 18

No Polyol Stickiness at 10 ° C Stickiness at 37 ° C Force (kPa) (kPa) peeled at 180 °

(N / cm)

22 UHC-50-200 0.23 ± 0.0 1188 ± 108 4.5 ± 0.3

Examples 23-25

Polyurethane PSA adhesives for application at low temperature. PSAs were prepared from MDI and mixtures of polypropylene glycol and 1,4-butanediol polyadipate both of molecular weight 2000 g / mol, with an NCO / OH ratio of 1.30. Table 19 shows the tack and peel strength values at 180 ° measured at 25 ° C, with adhesive cohesion failure observed when polypropylene glycol percentages greater than 50% by weight and adhesion failure were used for percentages of polypropylene glycol below 50% by weight, which showed good tack but low peel strength at 180 °. The values of Table 20 showed that at room temperature these PSAs had a viscous behavior (small values of G 'at low frequencies) characteristic of adhesives with high tack, while the G' values at low frequencies increased when the temperature decreased. -10 ° C.

Table 19

No D2021 (% F501 NCO / OH Stickiness to 25 Peel strength to weight) (% by weight) ° C (kPa) 180 ° (N / cm)

22 100 0 1.30 992 ± 26 0.1 ± 0.0

23 75 25 1.30 885 ± 9 0.6 ± 0.0

24 50 50 1.30 110 ± 7 0.1 ± 0.0 Table 20

Claims (15)

1. Pressure sensitive polyurethane thermoplastic adhesive with controlled tack as a function of temperature, comprising: - an isocyanate of general formula R (NCO) n, where n is at least 2, - at least one polyol or polyol mixture, where the NCO / OH ratio is greater than 1, the functionality is at least 2, and the molecular weight of the polyol or polyols is between 400-5000 g / mol, characterized in that it comprises: - a mixture of polyols wherein said polyols have a molecular weight of 400 g / mol, 1000 g / mol and 2000 g / mol, the percentage of polyols of molecular weight 2000 g / mol being less than 50% of the total thereof, and the NCO / OH ratio is comprised between 1.05-1.10, the adhesive having an optimum tack in the temperature range of between 10-39 ° C, or - a mixture of polyols wherein said polyols have a molecular weight of 1000 g / mol and 2000 g / mol, and the NCO / OH ratio is between 1.20-1.35, the adhesive having an optimum tack in the temperature range of between - 20 ° C, or - a mixture of polyols wherein said polyols have a molecular weight of 2000 g / mol, and the NCO / OH ratio is between 1.30-1.40 and where the polyol mixture comprises a mixture of polypropylene glycol and polyester polyol where the maximum amount of polyester polyol is 50% by total weight of the polyol mixture, the adhesive having an optimum tack in the temperature range between -10 - 5 ° C. The thermoplastic polyurethane adhesive according to claim 1, wherein the isocyanate is selected from aliphatic isocyanates, aromatic isocyanates derived from methylene diphenyl 4,4'-diisocyanate (MDI), isocyanates derived from 2,6-toluene diisocyanate (TDI) and isocyanate prepolymers. 3. The polyurethane thermoplastic adhesive according to any of claims 1-2, wherein the polyol or mixture of polyols is selected from polyether, polyester, polycaprolactone, polycarbonate diol and mixtures thereof. 4. Polyurethane thermoplastic adhesive according to any of claims 1-3, wherein the mixture of polyols comprises poly (tetrahydrofuran) and / or propylene glycols with weight molecular weight of 400 g / mol, 1000 g / mol and 2000 g / mol, the percentage of polyols of molecular weight 2000 g / mol being less than 50% of the total thereof and the NCO / OH ratio is between 1.05-1.10 . 5. The polyurethane thermoplastic adhesive according to claim 4, wherein the polyol mixture comprises polypropylene glycol and polycarbonate diol. 6. The polyurethane thermoplastic adhesive according to any of claims 1-3, wherein the polyol mixture comprises a mixture of propylene glycol with molecular weight of 1000 g / mol and poly (tetrahydrofuran) with molecular weights of 1000 g / mol and 2000 g / mol and the NCO / OH ratio is between 1.20-1.35. 7. A polyurethane thermoplastic adhesive according to any of claims 1-6, comprising a chain extender. 8. Support comprising a polyurethane thermoplastic adhesive according to any of claims 1-7. 9. Use of a polyurethane thermoplastic adhesive according to any of claims 1-7, on labels, prostheses, films, packaging tapes, and pharmaceuticals. 10. Process for the preparation of a pressure sensitive polyurethane thermoplastic adhesive with controlled tack as a function of the temperature according to any of claims 1-7, comprising the following steps: a) mixture of an isocyanate or mixtures of isocyanates, and a polyol or mixture of polyols as defined in claim 1 b) catalyst addition, c) titration of the free NCOs in the reaction, until an NCO / OH ratio greater than 1 is achieved, as defined in claim 1, d) addition of chain extender until polyurethane is obtained. 11. Process for the preparation of a pressure sensitive polyurethane thermoplastic adhesive with temperature-controlled tack according to claim 10, wherein the isocyanate of step a) is selected from aliphatic isocyanates, aromatic isocyanates derived from methylene diphenyl 4,4'-diisocyanate (MDI), isocyanates derived from 2,6-toluene diisocyanate (TDI) and isocyanate prepolymers. 12. Procedure for the preparation of a pressure sensitive polyurethane thermoplastic adhesive with controlled tack as a function of temperature according to any of claims 10-11, wherein the polyol or polyol mixture of step a) is selected from polyether, polyester, polycaprolactone, polycarbonate diol and mixtures thereof. 13. Process for the preparation of a pressure-sensitive thermoplastic polyurethane adhesive with controlled tack as a function of the temperature according to any of claims 10-12, wherein the catalyst of step b) is an organic tin catalyst. 14. Process for the preparation of a pressure sensitive polyurethane thermoplastic adhesive with temperature-controlled tack according to any of claims 10-13, wherein the chain extender of step d) is selected from diol or diamine . 15. Process for the preparation of a pressure sensitive polyurethane thermoplastic adhesive with controlled tack as a function of the temperature according to any of claims 10-14, wherein the reaction time of step d) is 10 minutes.