MX2010014334A - Pressure sensitive adhesives which are self-crosslinkable at room temperature. - Google Patents

Abstract

Use of water-based polymers as pressure sensitive adhesives, which are formed by units of one or several monomers which polymers present the characteristic of having a very low glass transition temperature, such as the butyl acrylate, 2-ethylhexyl acrylate or the diisooctyl acrylate, amongst others, in a ratio of from about 30% to about 95% by weight with regard to the total mixture of monomers; one or a plurality of monomers which polymers have a higher glass transition temperature, such as the ethyl acrylate, the methyl acrylate, the vinyl acrylate or the methyl methacrylate, amongst others, in a ratio of from about 5% to about 60% by weight with regard to the total mixture of monomers; also includes units of 3-isopropenyl-a, a-dimethyl bencyl isocyanate monomer, TMI, in a ratio of from about 0.5% to about 10% by weight with regard to the total mixture of monomers.

Description

SELF-RETICULABLE PRESSURE SENSITIVE ADHESIVES AT ROOM TEMPERATURE" DESCRIPTION OBJECT OF THE INVENTION The object of the present invention is to protect the use as pressure sensitive adhesives of copolymers whose characteristic is that they are formed with units of one or more monomers whose polymers have the characteristic of having a very low vitreous transition temperature, such as butyl acrylate, 2-ethylhexyl acrylate or isooctyl acrylate, among others; one or more monomers whose polymers have a higher vitreous transition temperature, such as ethyl acrylate, methyl acrylate, vinyl acetate or methyl methacrylate, among others; as well as units of the isocyanate monomer of 3-isopropenyl-α, α-dimethylbenzyl, TMI, whose function is to generate crosslinking points between the polymer chains. The crosslinking reactions caused by the TMI can occur at room temperature and the adhesives have better swelling properties with water and other solvents.

BACKGROUND Pressure sensitive adhesives (PSAs) are those that adhere to a substrate quickly and firmly under the application of light pressure. Two of the main characteristics of this type of materials are the adhesion (the force with which the adhesive is attached to the surface of the substrate) and the cohesion (the internal force between the molecules of the adhesive film). A PSA must show strong adhesion to the substrate without generating any chemical type bond in the interface [C. Creton in Materials Science and Technology: A Comprenhensive Treatment, H.E. H. Meijer (Ed.), Vol. 18, p. 708, VCH, Weinhein, Germany, 1997] The quality of a self-adhering article depends mainly on the relationship between the adhesion and the cohesion of the adhesive layer. This relationship can be designed according to each application. In the case of a protective tape, a low adhesion combined with a very high cohesion is sought, because it is required that after a long period of time, the tape can be removed, without leaving any residue of the adhesive on the substrate that originally protected On the other hand, in the case of adhesive tapes for packaging, the adhesive layer needs the combination of a high adhesion and a high cohesion [M. C. Bricker and S. T. Gentry, Adhesives Age, Jury, 30-33, 1994].

Currently, in the production of PSAs there is a tendency to substitute solvent-based systems for water-based systems that have certain advantages compared to the former [D. J. Dunn and R. H. D. Beswick, Natural and Synthetic Latex Polymers Market Report, Rapra Technology Limited, Shawbury, Shrewsbury, Shropshire, SY4 4NR, UK, 2002]. Unlike a solvent-based system, the viscosity of a water-based system does not depend on the molecular weight of the polymer, since it is contained within the latex particles. The viscosity of these systems depends on the size of the particles and the solids content. Normally, a latex with a content of 35-55% of solids has a relatively low viscosity (<1000 cp), while solvent based products of a similar viscosity have solids contents < 30 Adhesion and cohesion strongly depend on the formulation of the adhesive. If an adhesive must be adapted to a certain application or process conditions, one of the main parameters that can be altered is the composition in the monomer mixture used. Butyl acrylate (BA) and 2-ethylhexyl acrylate (2-EHA) are the most used monomers for the development of this type of adhesives and, in most cases, is the main compound in the formulation [S . Kirsch, M. Kutschera, N. Y; Frechen, J. Appl. Polym. Sci., 101, 1444, 2006; M. D. Gower, R. A Shanks, J. Appl. Polym. Sci., J. Polym. Sci. Part. B: Polym Phys, 44, 1237, 2006; S. Jitladda, T. Narumol, P. Nanthaporn, T. Yasuyuki, J. Appl. Polym. Sci., 100, 413, 2006; M. D. Gower, R. To Shanks, Macromol. Chem. Phys, 205, 2139, 2004]. Another monomer that is also used for this purpose is vinyl acetate (VA) copolymerized with BA. [M. Sanmiguel, N. Soto, Y. Reyes, F. Vázquez, Int. J. Polym. Mat., 55, 595, 2006; N. Soto, M. Sanmiguel, Y. Reyes, M. A. Duda, F. Vázquez, Int. J. Polym. Mat., 55, 187, 2006; R. Jovanovic, M. A. Dubé, Ind. Eng. Chem. Res., 44, 6668, 2005]. It is also common the use of bifunctional monomers that promote excellent adhesion to the substrate, at the same time favoring the crosslinking of the chains to give a greater cohesion to the film, such as acrylic acid (AA) and acrylamide (AM) [S. Kirsch, M. Kutschera, N. Y. Frechen, J. Appl. Polym. Sci., 101, 1444, 2006; M. D. Gower, R. A Shanks, J. Appl. Polym. Sci., J. Polym. Sci. Part. B: Polym Phys, 44, 1237, 2006; S. Jitladda, T. Narumol, p. Nanthaporn, T. Yasuyuki, J. Appl. Polym. Sci., 100, 413, 2006; M. D. Gower, R. To Shanks, Macromol.

Chem. Phys, 205, 2139, 2004; M. Sanmiguel, N. Soto, Y. Reyes, F. Vázquez, Int. J. Polym. Ma, 55, 595, 2006; N. Soto, M. Sanmiguel, Y. Reyes, M. A. Duda, F. Vázquez, Int. J. Polym. Mat., 55, 187, 2006; R. Jovanovic, M. A. Dubé, Ind. Eng. Chem. Res., 44, 6668, 2005]. However, in a process of emulsion polymerization, the use of a monomer such as acrylic acid is not without collateral effects, unlike what occurs in solvent-based processes, where these types of limitations have not been observed.

With respect to the surfactant, this component of the formulation has a great impact in all the stages of production of the latex, since it controls the number of particles formed, their distribution of sizes and the stability of the finished product. It could be said that there is a suitable surfactant system for each application, so that its selection is of great importance if it is desired to achieve an optimum performance of the adhesive [J. Mallegol, O. Dupont, J. L. Keddie, J. Adhesion Sci. Technol., 17, 243, 2003]. Depending on the type of surfactant and the drying conditions, an excess of surfactant may be located at the PS A / substrate interface and at the PS A / air interface, which may have an important influence on the adhesion properties [J. Y. Charmeau, P. A. Gerin, L. Vovelle, R. Schirrer, Y. Holl., J. Adhesion Sci. Technol., 13, 203, 1999; A. Zosel, B. Schuler, J. Adhesion 70, 179, 1999].

The bifunctional isocyanate monomer of 3-isopropenyl-α, α-dimethylbenzyl, TMI, is a monomer that combines a vinyl unsaturation with an isocyanate group, -NCO, such that it can react with the double bond to form a copolymer and, subsequently, react with the -NCO group to generate the crosslinking of the polymer chains [S. Mohammed, E.S. Daniels, A. Klein and M.S. El-Aasser, J. Appl. Polym. Sci., 61, 91 1, 1996; R.W. Dexter, R. Saxon and D.S. Fiori, J. Coat. Teph., 58, 43, 1986]. It has been found that films prepared from latex of the terpolymer formed by methyl methacrylate, butyl acrylate (BA) and TMI have better mechanical properties due to the crosslinking caused by the TMI [S. Mohammed, E.S. Daniels, L.H. Sperling, A. Klein and M.S. The Aasser, J. Appl. Polym. Sci., 66, 1869, 1997].

Based on the foregoing, the object of the present invention is to protect the use as pressure sensitive adhesives of water-based copolymers prepared by the technique of emulsion polymerization whose characteristic is that they are formed with units of one or more monomers whose polymers have the characteristic of having a very low vitreous transition temperature, such as butyl acrylate, 2-ethylhexyl acrylate or isooctyl acrylate, among others; one or more monomers whose polymers have a higher vitreous transition temperature, such as ethyl acrylate, methyl acrylate, vinyl acetate or methyl methacrylate, among others; as well as units of the isocyanate monomer of 3-isoproperul-a, a-dimethylbenzyl, TMI, whose function is to generate crosslinking points between the polymer chains. The crosslinking reactions caused by the TMI can occur at room temperature and the adhesives have better swelling properties with water and other solvents.

DETAILED DESCRIPTION OF THE INVENTION Different latexes were prepared, by emulsion copolymerization of a monomer mixture formed by different proportions, butyl acrylate, vinyl acetate and TMI, which were evaluated as PSAs, finding that the presence of TMI caused the crosslinking of the polymer and a increase in the cohesive force (holding power) of the pressure-sensitive adhesives and a decrease in the degree of swelling of the polymer with toluene.

The copolymers that are the basis of self-crosslinkable PSAs at room temperature are composed of units of one or more monomers whose polymers have the characteristic of having a very low vitreous transition temperature, such as butyl acrylate, acrylate 2- ethylhexyl or isooctyl acrylate, inter alia, in a range of 30 to 95% by weight with respect to the total monomer mixture; one or more monomers whose polymers have a higher vitreous transition temperature, such as ethyl acrylate, methyl acrylate, vinyl acetate or methyl methacrylate, inter alia, in a range of 5 to 60% by weight with respect to the total monomer mixture; in addition to units of the isocyanate monomer of 3-isopropenyl-α, α-dimethylbenzyl, TMI, in a range from 0.5 to 10% by weight with respect to the total monomer mixture.

The polymer can be prepared by free radical polymerization using a process of emulsion polymerization, suspension, mini-emulsion, microemulsion or any other type of heterophase polymerization that allows obtaining polymer particles dispersed in water. For the stabilization of the particles, one or more surfactants may be used, which may be cationic, anionic, nonionic or polymeric, among others. Once the latex is obtained, it can be formulated with the addition of different fillers and additives such as thickeners, fungicides, pH modifiers, among others, necessary to increase its shelf life and improve its application in its final use as a wood adhesive. The adhesive can be used for the manufacture of pressure-sensitive products such as adhesive tapes for different applications, labels, self-adhesive protective films, among others. In addition, the different chemical reactions originated by the -NCO groups of the TMI can be carried out at room temperature or be accelerated by the use of heat, catalytic agents or radiofrequency, among other methods.

The invention having been described in a general manner, an exemplary embodiment is described below that serves only as an illustration of the procedure and is not intended to be limiting in any way.

EXAMPLE 1 Using a 500 mL jacketed glass reactor, 3 latexes were prepared by the emulsion polymerization technique. The formulation used is presented in Table 1.

Table 1. Formulation used in the preparation of the pressure sensitive adhesives The reactor was charged with a part of the total water of the system (210 g), as well as the total surfactant, sodium bicarbonate and VA. With the remaining water (40 g) the solutions of the redox initiators (potassium persulfate and potassium metabisulfite) were prepared, which were added in semicontinuous in two individual streams.

The mixture was stirred at 200 rpm and was bubbled with argon for 1.5 h, while cold water was passed through the jacket of the reactor to prevent entrainment of monomer by the argon stream. After this time, the heating of the reaction mixture was started, passing hot water through the jacket of the reactor After 30 min, time g sufficient to reach a temperature of 40 ° C, the semicontinuous addition of the monomer mixture (total BA, TMI and terdodecyl mercaptan), as well as the solutions of the oxidant (potassium persulfate) and the reducer (metabisulfite of potassium). The bubbling with argon was continued until the end of the reaction. The semicontinuous addition was made at different times (4 and 6 h). In Table 2.

Table 2. Properties of pressure sensitive adhesives.

Claims (10)

CLAIMS Having sufficiently described the invention, the authors consider as a novelty and therefore claim as their exclusive property, what is contained in the following clauses:

1. The object of the present invention is to protect the use as pressure sensitive adhesives of copolymers whose characteristic is that they are formed with units of one or more monomers whose polymers have the characteristic of having a very low vitreous transition temperature, such as butyl acrylate, 2-ethylhexyl acrylate or isooctyl acrylate, among others; units of one or more monomers whose polymers have a higher vitreous transition temperature, such as ethyl acrylate, methyl acrylate, vinyl acetate or methyl methacrylate, among others; in addition to isocyanate monomers of 3-isopropenyl-a, or dimethylbenzyl, TMI.

2. The copolymers of claim 1, characterized in that they contain units of one or more monomers whose polymers have a very low vitreous transition temperature such as butyl acrylate, 2-ethylhexyl acrylate or isooctyl acrylate, among others, in a range which ranges from 30 to 95% by weight with respect to the total monomer mixture used in the copolymerization reaction.

3. The copolymers of claim 1, characterized in that they contain units of one or more monomers whose polymers have a higher vitreous transition temperature such as ethyl acrylate, methyl acrylate, vinyl acetate or methyl methacrylate, among others, between others, in a range ranging from 5 to 60% by weight with respect to the total monomer mixture used in the copolymerization reaction.

The copolymers of claim 1, characterized in that they contain units of the bifunctional monomer TMI, whose function is to generate crosslinking points between the polymer chains, in a range ranging from 0.5 to 10% by weight with respect to the total monomer mixture used in the copolymerization reaction.

The copolymers of claim 1 characterized in that they can be prepared by free-radical polymerization using a process of emulsion polymerization, suspension, mini-emulsion, microemulsion or any other type of heterophase polymerization that allows obtaining polymer particles dispersed in water.

The copolymers of claim 1 characterized in that the polymer particles can be stabilized with a cationic surfactant such as dodecyltrimethylammonium bromide, didodecyldimethylammonium bromide and hexadecyltrimethylammonium bromide, of the anionic type such as sodium dodecyl sulfate and bis (2-) ethylhexyl) sodium sulfosuccinate, of non-ionic type such as nonylphenol ethoxylated with "n" moles of ethylene oxide, where "n" must be greater than 6, or polymeric type such as polyvinyl alcohol.

The copolymers of claim 1 characterized in that they can be formulated with the addition of different fillers and additives such as thickeners, fungicides, pH modifiers, among others, necessary to increase their shelf life and improve their application in their final use as sensitive adhesives. the pressure.

8. The copolymers of claim 1 characterized in that they can be applied on different materials that function as backup, such as films, plastic, paper films, among others.

9. The copolymers of claim 1 characterized in that they can be used for making, tapes, labels and any type of self-adhering film.

10. The copolymers of claim 1 characterized in that the chemical reaction of the -NCO groups can be carried out at room temperature or be accelerated by the use of heat, catalytic agents or radiofrequency, among other methods.