EP1290102A1 - Anwendung von sternförmigen polymeren in druckempfindlichen klebemitteln - Google Patents

Anwendung von sternförmigen polymeren in druckempfindlichen klebemitteln

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Publication number
EP1290102A1
EP1290102A1 EP00936446A EP00936446A EP1290102A1 EP 1290102 A1 EP1290102 A1 EP 1290102A1 EP 00936446 A EP00936446 A EP 00936446A EP 00936446 A EP00936446 A EP 00936446A EP 1290102 A1 EP1290102 A1 EP 1290102A1
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EP
European Patent Office
Prior art keywords
pressure sensitive
sensitive adhesive
esters
acrylate
monomers
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP00936446A
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English (en)
French (fr)
Inventor
Robert D. Harlan
Jules E. Schoenberg
Christopher G. Gore
Deepak Hariharan
Smita M. Shah
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
National Starch and Chemical Investment Holding Corp
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National Starch and Chemical Investment Holding Corp
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Publication date
Application filed by National Starch and Chemical Investment Holding Corp filed Critical National Starch and Chemical Investment Holding Corp
Publication of EP1290102A1 publication Critical patent/EP1290102A1/de
Withdrawn legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F2/00—Processes of polymerisation
    • C08F2/12—Polymerisation in non-solvents
    • C08F2/16—Aqueous medium
    • C08F2/18—Suspension polymerisation
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F293/00—Macromolecular compounds obtained by polymerisation on to a macromolecule having groups capable of inducing the formation of new polymer chains bound exclusively at one or both ends of the starting macromolecule
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J153/00—Adhesives based on block copolymers containing at least one sequence of a polymer obtained by reactions only involving carbon-to-carbon unsaturated bonds; Adhesives based on derivatives of such polymers

Definitions

  • This invention relates to the use of star-branched polymers in pressure sensitive adhesive applications.
  • Star-branched polymers also known as radial polymers, are characterized by having three or more polymeric arms emanating from a central core. These polymers can be prepared by various polymerization procedures such as anionic, cationic, and free radical mechanisms.
  • the star polymers are usually formed by using either multifunctional initiators, multifunctional chain transfer agents, or multifunctional coupling agents.
  • the star polymers have unique properties including: narrow molecular weight distributions; low viscosities at low molecular weights or in solution due to their compact structures; and high viscosities at high molecular weights due to extensive entanglements.
  • 3,769,254 discloses pressure sensitive adhesives prepared from linear polymers of acrylic polymers containing monomers with reactive hydrogen groups.
  • high molecular weight linear polymers are usually used in high performance applications.
  • Such polymers have solution viscosities proportional to their molecular weight. Attempts to lower the solution viscosities by reducing molecular weight results in a reduction in adhesive properties which makes them difficult to use as hot melts for high performance and coating applications. In linear systems, these lost properties cannot be recovered by crosslinking.
  • U.S. Patent No. 5,679,762 discloses block star polymers which overcome some of the problems associated with a linear system. This patent is limited to block polymers which provide phase separation to attain the desired adhesive properties.
  • SUMMARY OF THE INVENTION This invention relates to pressure sensitive applications comprising star polymers. Specifically to pressure sensitive applications comprising random star polymers comprising an olefinic monomer containing one or more functional groups which can be crosslinked by reaction with multifunctional crosslinking agents.
  • the pressure sensitive adhesive compositions of the present invention comprise an adhesive polymer formed by the reaction of a multifunctional crosslinker with a star polymer.
  • Optional components of the adhesive polymer include other monomers containing an additional copoiymerizable ethylenically unsaturated linkage as the only reactive functional group.
  • the preferred multifunctional crosslinkers are metal compounds.
  • Figure 1 is a graph of viscosity as a function of percent acrylic acid.
  • Figure 2 is a graph of 20 minute peel as a function of percent acrylic acid.
  • Figure 3 is a graph of 24 hour peel as a function of percent acrylic acid.
  • Figure 4 is a graph of loop tack as a function of percent acrylic acid.
  • Figure 5 is a graph of shear hold as a function of percent acrylic acid.
  • the pressure sensitive adhesives of the present invention comprise an adhesive polymer formed by the reaction of a star polymer and multifunctional crosslinker.
  • the star polymers of the present invention comprise a polyvalent mercaptan core and three or more polymeric arms which extend radially from the core. The compositions of the arms themselves are random polymers.
  • the polyvalent mercaptan core of the present invention comprises three or more thiol groups.
  • the thiol groups can be either all the same or all different or variations therein. It is at the thiol groups that the monomers will react to create the polymeric arms of the star polymer.
  • the polyvalent mercaptan core comprises a central component, derived from a multifunctional alcohol which has been substituted with thiol derivatives.
  • the multifunctional alcohol can have any number of functional hydroxy units, preferably three to eight functional units.
  • each of the OH functional units will be substituted with thiol units.
  • the core compositions range from a tri-functional alcohol substituted with three identical thiol groups, up to an octa-functional alcohol substituted with eight different thiol groups.
  • the polyvalent mercaptan core is of the general formula:
  • X is derived from a tri- to octa- multi-functional alcohol such as glycerol, sorbitol, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, and inositol.
  • a tri- to octa- multi-functional alcohol such as glycerol, sorbitol, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, and inositol.
  • Variables Y.,, Y 2 , Y 3 , Y 4 , Y 5 , Y 6 , Y 7 and Y 8 are the same or different and each comprises C 2 . 10 alkanoic acids, preferably C 2 . 6 alkanoic acids.
  • Variables a, b, c, d, e, f, g and h are integers from 0 to 8 provided that a+b+c+d+e+f+g+h ⁇ 8.
  • a and b are integers from 1 to 8
  • c, d, e, f, g, h are integers from 0 to 8 provided that a+b+c+d+e+f+g+h ⁇ 8.
  • Each of the above identified (Y-SH) units are derived from, for example, 2- mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, 4- mercaptobutyric acid, 5-mercaptopentanoic acid, or 6-mercaptohexanoic acid. Preferred are 2-mercaptopropionic acid and 3-mercaptopropionic acid.
  • Examples of cores of differential reactivity include pentaerythritol bis(3- mercaptopropionate) bis(2-rnercaptopropionate); trimethylolpropane bis(3- mercaptopropionate)(2-mercaptopropionate); pentaerythritol tris(3-mercaptopropionate)(2- mercaptopropionate); and trimethylolpropane bis(2-mercaptopropionate) (3- mercaptopropionate).
  • Cores of non-differential reactivity, or homocores include pentaerythritol tetrakis(3-mercaptopropionate), trimethylolpropane trithiopropionate, tri(3-mercapto propionate), pentaerythritol tetrakis(thioglycolate) and dipentaerythritol hexakis thioglycolate.
  • the polyvalent mercaptan core is prepared by reacting a multi-functional alcohol with the appropriate amount of mercapto acid to prepare the polyvalent mercaptan core.
  • the multifunctional alcohol is a tri-alcohol
  • three equivalents of mercapto acid are added to give three (HS-Y) units.
  • the three equivalents of mercapto acid can be made up of any combination of the preferred mercapto acids.
  • one equivalent of 2-mercaptopropionic acid (a secondary thiol-containing acid) and two equivalents of 3-mercaptopropionic acid (a primary thiol-containing acid) will provide a core of differential reactivity.
  • the alcohol is a trialcohol and three equivalents of 2- mercaptopropionic acid are used, a homocore within the scope of the present invention is also obtained.
  • pentaerythritol can be used as the multifunctional alcohol, X, used to prepare the core.
  • X the multifunctional alcohol
  • the result will be a mixture of five compounds corresponding to molecules containing ratios of primary/secondary SH groups of 0/4, 1/3, 2/2, 3/1 , and 4/0.
  • Those cores with ratios of 1/3, 2/2 and 3/1 have differential reactivity and are within the scope of the present invention.
  • the cores with 0/4 and 4/0 are homocores.
  • the product mixture though a statistical mixture, has cores with an average of two primary thiol groups and two secondary thiol groups per core as shown by the following reaction: The reaction is shown below:
  • dipentaerythritol seven possible compounds can be obtained corresponding to 0,1 ,2,3,4,5 and 6 primary SH groups per molecule. These differential thiols will be utilized to provide enhanced selectivity to generate heteroarm stars.
  • the star polymers of the present invention are formed using the mercaptan core as a chain transfer agent in polymerization processes which include bulk, solution, emulsion, and suspension polymerization.
  • the process is a solution polymerization process employing a free radical initiator.
  • the polymerization reaction is typically conducted at temperatures in the range of 10 to 120°C, preferably 70 to 100°C.
  • the resulting polymer may comprise arms that are all the same, or all the same after the S atom but with different Y connecting groups.
  • the preparation of the star polymers of the present invention is by the non-sequential addition of monomers to the mercaptan core.
  • the core may be a core of differential reactivity, or a homocore.
  • all of the monomers are added at the same time, i.e., a mixture of two or more monomers are added to the core.
  • the core is a core of differential reactivity, the monomers with the higher reactivity ratios in copolymerization will react with the most reactive thiol groups.
  • the core is a homocore, the mixture of monomers will react randomly leading to random polymeric arms on the resulting star polymer.
  • the polymerization is initiated by a mercapto group on the polyvalent mercaptan core.
  • the orders of reactivity of thiol groups are: SH groups attached to aromatic rings (i.e., thiophenols) are more reactive than SH groups attached to primary aliphatic carbon atoms which are more reactive than SH groups attached to secondary aliphatic carbon atoms, i.e., ArSH>RCH 2 SH> RR'CHSH.
  • the monomer mixtures can be added by any method familiar to the skilled artisan including dropwise or by slug dose.
  • Monomers which may be used to prepare the polymeric arms of the star polymers of the present invention include olefinically unsaturated monomers in addition to a small amount of an olefinic monomer containing crosslinkable functionality such as alcohols, acids, isocyanates, epoxides and combinations thereof.
  • olefinically unsaturated monomers include those selected from the group consisting of acrylic and methacrylic acids, acrylamide and methacrylamide, acrylonitrile and methacrylonitrile, alkoxyalkyl acrylamides and methacrylamides, e.g., butoxymethyl acrylamide and methoxymet yl methacrylamide, hydroxyalkyl acrylamides and methacrylamides, e.g., N-methylol acrylamide and methacrylamide.
  • esters and amides of acrylic and methacrylic acids with alcohols, phenols and amines are preferred.
  • the vinyl aromatic compounds e.g., styrene, alpha -methylstyrene and substituted derivatives thereof such as the halogenated derivatives thereof and vinyl toluene
  • Monomers may be selected from hydroxyalkyl esters of ethylenically unsaturated carboxylic acids, ethylenically unsaturated carboxylic acids, ethylenically unsaturated epoxides, ethylenically unsaturated isocyanates and combinations thereof.
  • unsaturated monomers include hydroxypropyl (meth)acrylate, glycidyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, ethoxyethoxyethyl (meth)acrylate, cyanoethyl acrylate and the like; vinyl ethers which are represented by methyl vinyl ether, ethyl vinyl ether, isobutyl vinyl ether, and the like; fumaric acid, monoalkyl fumarates, dialkyl fumarates; maleic acid, monoalkyl maleates, dialkyl maleates; itaconic acid, monoalkyl itaconates, dialkyl itaconates; half esters of succinic anhydride or phthalic anhydride with hydroxyethyl (meth)acrylate; (meth)acrylonitrile, butadiene, isoprene, vinyl chloride, vinylidene chloride, vinyl keto
  • the present invention also contemplates the use of multifunctional monomers such as ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, diethylene glycol di(meth)acrylate trisacrylate, divinyl benzene, triallyl cyanurate, allyl acrylate, diallyl phthalate, diallyl sucrose and allyl(meth)acryalate.
  • the preferred monomers are acrylic acid and methacrylic acid and derivatives such as esters and amides which have chain transfer constants with thiols that are close to one.
  • Examples of such monomers include acrylic and methacrylic acid and esters of acrylic acid and methacrylic acid such as methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate, isobomyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, cyclohexyl methacrylate, isobomyl methacrylate, 2-ethylhexyl methacrylate, benzyl methacrylate, phenyl methacrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate.
  • acrylic and methacrylic acid and esters of acrylic acid and methacrylic acid such as methyl
  • the alkyl acrylates will form a major essential constituent of the polymeric arms of the star polymer.
  • Such alkyl acrylates are preferably acrylic acid esters of alcohols having up to about 18 carbon atoms.
  • the preferred alkyl acrylates have an average of from about 4 to about 10 carbon atoms in the alkyl groups, and include butyl acrylate, amyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, nonyl acrylate, decyl acrylate, and various isomers of these acrylates, such as isooctyl acrylate.
  • One specific preferred alkyl acrylate for use in the invention is 2-ethylhexyl acrylate.
  • Higher alkyl acrylates can in some instances be used, particularly in combination with the lower alkyl acrylates, whereby the average number of carbon atoms in the alkyl groups is within the desired range.
  • Methyl methacrylate, 2-ethylhexyl acrylate, methyl acrylate, acrylic acid, butyl methacrylate, 2-hydroxyethyl acrylate, t-octyl acrylamide and butyl acrylate are the most preferred monomers.
  • the polymeric arms of the star polymer also include a small amount of an olefinic monomer containing crosslinkable functionality such as alcohols, acids, isocyanates, epoxides and combinations thereof.
  • an olefinic monomer containing crosslinkable functionality such as alcohols, acids, isocyanates, epoxides and combinations thereof.
  • examples of such monomers include, but are not limited to, hydroxyalkyl esters o f ethylenically unsaturated carboxylic acids, ethylenically unsaturated carboxylic acids, ethylenically unsaturated epoxides and ethylenically unsaturated isocyanates.
  • the preferred olefinic monomers that are crosslinkable include the ethylenically unsaturated carboxylic acids.
  • the preferred carboxylic acids are acrylic acid and methacrylic acid, but other copoiymerizable acids such as crotonic acid, itaconic acid, and fumaric acid can also be employed.
  • Other useful carboxylic acids include half esters of unsaturated dicarboxylic acids such as methyl hydrogen fumarate, butyl hydrogen fumarate, ethyl hydrogen maleate, and butyl hydrogen maleate. These agents may be present in amounts from about 0.2 percent up to about 20 percent by weight of the total weight of the star polymer.
  • Preferred products contain from about 0.3 to about 10 percent by weight of such acids.
  • hydroxyalkyl esters of ethylenically unsaturated acids include hydroxyalkyl esters of ethylenically unsaturated acids.
  • the preferred hydroxyalkyl esters are esters of acrylic acid, methacrylic acid, and other alpha-beta ethylenically unsaturated carboxylic acids. Examples include 3-hydroxyethyl acrylate, 2-hydroxpropyl acrylate, 3- hydroxypropyl acrylate, 2-hydroyethyl methacrylate, 2-hydroxpropyl methacrylate, 3- hyroxypropyl methacrylate, 4-hydroxybutyl methacrylate, and corresponding esters of other unsaturated acids.
  • methacrylic acid for example, methacrylic acid, crotonic acid, and similar acids of up to about six carbon atoms.
  • mono- or di-esters of unsaturated dicarboxylic acids such as maleic acid, fumaric acids, and itaconic acid in which at least one of the esterifying groups contains a hydroxyl group.
  • esters examples include mono(2-hydroxyethyl) maleate, mono(2-hydroxyethyl) fumarate, bis(2- hydroxyethyl) maleate, mono(2-hydroxypropyl) maleate, bis(2-hydroxypropyl) maleate, mono(2-hydroxyethyl) itaconate, bis(2-hydroxyethyi) itaconate, and 2-hydroxyethylbutyl maleate.
  • a preferred ethylencially unsaturated epoxide is glycidyl (meth)acrylate, (“GMA”).
  • a preferred ethylencially unsaturated isocyanate is 1-(1-isocyanato-1 -methyl ethyl)-3-(1 -methyl ethenyl)benzene (“m-TMI”).
  • the arms of the star polymer are prepared from monomers consisting essentially of one or more alkyl acrylates, generally containing up to about 10 carbon atoms in the alkyl group, along with a small proportion of an acrylic monomer having crosslinkable functionality such as hydroxyalkyl esters of ethylenically unsaturated carboxylic acids, ethylenically unsaturated carboxylic acids, ethylenically unsaturated epoxides and ethylenically unsaturated isocyanates.
  • an acrylic monomer having crosslinkable functionality such as hydroxyalkyl esters of ethylenically unsaturated carboxylic acids, ethylenically unsaturated carboxylic acids, ethylenically unsaturated epoxides and ethylenically unsaturated isocyanates.
  • the polymeric arms also may include one or more other additional copoiymerizable monomers devoid of any functional group except for the polymerizable ethylenic linkage. In many cases it may be desirable to have both copoiymerizable monomers containing OH groups and those containing COOH groups in the composition simultaneously.
  • acrylate monomers such as methyl acrylate and methyl methacrylate, which are not considered tacky or pressure sensitive, may be used in combination with the acrylic monomers, or with the combination of acrylic and vinyl monomers, known to have pressure sensitivity.
  • combinations of acrylic and vinyl monomers known to have pressure sensitivity can be used.
  • the total amount of the monomer will be such that the monomers known to impart pressure sensitivity will constitute at least about 50% by weight of the total copolymer.
  • the vinyl monomers that may be used in combination with the acrylic monomers include vinyl monomers selected from the group consisting of vinyl esters, vinyl ethers, vinyl halides, vinylidene halides, and nitriles of ethylenically unsaturated hydrocarbons, and include, vinyl acetate, vinyl ethyl ether, vinyl chloride, vinylidene chloride, and acrylonitrile.
  • the star polymer composition there can also be included in the star polymer composition one or more other copoiymerizable monomers which contain an ethylenically unsaturated linkage, such linkage being the only reactive functional group in the monomer.
  • a vinyl ester of a saturated carboxylic acid such as vinyl acetate, vinyl propionate or vinyl butyrate.
  • Other optional monomers which will copolymerize by addition reaction include alkyl acrylates other than those above, and alkyl methacrylates having from 1 to 20 carbon atoms or more in the alkyl group, such as methyl methacrylate, butyl methacrylate, octadecyl methacrylate, lauryl methacrylate, and the like.
  • the exact relative amounts of the specific components making up the arms of the star polymers are dependent upon the final properties desired and the end uses contemplated, and are known in the art.
  • the process of the present invention is adaptable to be used with all such pressure sensitive adhesives.
  • the star polymer can include essentially any ethylenic monomer or mixture of monomers copoiymerizable with the other components and which do not contain additional crosslinkable functionality and which do not, in combination with those components, provide unsatisfactory properties such as unsatisfactorily reduced tack.
  • crosslinkable functionality herein refers to functional groups with which the multifunctional crosslinking agent reacts, such as hydroxyl, carboxyl, etc.
  • Such other monomers can be of widely varying types, depending upon the specific alkyl acrylates, hydroxyalkyl esters, carboxylic acids, and other monomers in the star polymer.
  • mono- olefinic hydrocarbons such as styrene and vinyl toluene
  • halogenated mono-olefinic hydrocarbons such as vinyl chloride and vinylidene chloride
  • unsaturated esters such as isopropenyl acetate and dimethyl maleate
  • dienes such as 1 ,3-butadiene.
  • the polymer arm of the resulting polymer comprises 10 to 1500 monomer units, preferably 20 to 500.
  • the copolymer is a random copolymer of such units.
  • Free radical initiators suitable for use in the polymerization process of the present invention include, for example: azo-based polymerization initiators such as 2,2'- azobisisobutyronitrile ("AIBN") and 2,2'-azobis(cyclohexanecarbo-nitrile); peroxide-based polymerization initiators such as benzoyl peroxide; and the like.
  • Suitable initiators include organic peroxides, hydroperoxides, persulfates and azo compounds such as methyl ethyl ketone peroxide, cumene hydroperoxide, potassium persulfate, lauroyl peroxide, 2,5- dimethyl-2,5-di(t-butylperoxy)hexane, diethyl peroxide, dipropyl peroxide, dilauryl peroxide, dioleyl peroxide, distearyl peroxide, di(tertiary butyl) peroxide, di(tertiary amyl) peroxide, tertiary butyl hydroperoxide, tertiary amyl peroxide, acetyl peroxide, propionyl peroxide, lauroyl peroxide, stearoyl peroxide, malonyl peroxide, succinyl peroxide, phthaloyl peroxide, acetyl benzoyl peroxid
  • a solvent can be selected from the group consisting of organic solvents which are represented by: aromatic hydrocarbons such as toluene and xylene; esters such as ethyl acetate and butyl acetate; cycloaliphatic hydrocarbons such as cyclohexane; aliphatic hydrocarbons such as hexane and pentane; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aliphatic esters; alcohols; and the like.
  • organic solvents which are represented by: aromatic hydrocarbons such as toluene and xylene; esters such as ethyl acetate and butyl acetate; cycloaliphatic hydrocarbons such as cyclohexane; aliphatic hydrocarbons such as hexane and pentane; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl
  • the star polymer as described above, is reacted with a multifunctional crosslinking agent to provide the adhesive polymer employed in the invention.
  • multifunctional crosslinking agents include soluble metal compounds, polyisocyanates, polyaziridines or polyepoxides.
  • metal alkoxides such as those having the formula R n T(OR 1 ) z , wherein T is a metal selected from those having valences of 2 to 5, such as aluminum, titanium, zinc, tin and zirconium.
  • R is selected from the group consisting of alkyl or alkoxy radicals of from 1 to 8 carbon atoms such as methyl, ethyl butyl, iso-octyl and the like, aryl radicals of from 6 to 16 carbon atoms such as benzyl, alkoxy radicals of from 1 to 8 carbon atoms, and moieties derived from beta-diketones such as acetyl acetonate.
  • R 1 is selected from the group consisting of aliphatic and substituted aliphatic radicals containing from 1 to 18 carbon atoms, such as alkyl groups, allyl groups and the like; n is an integer whose value is zero or greater and z is an integer of at least two, wherein the sum of n+z is greater than one (1 ) and is equal to the valence of the metal represented by T.
  • the preferred metal alkoxides are aluminum isopropoxide or titanium esters such as alkyl titanates such as ortho titanic acid esters of monofunctional alcohols and tetraaryl esters.
  • alkyl titanates include tetramethyl titanate, tetraethyl titanate, tetrapropyl titanate, tetraisopropyl titanate, tetrabutyl titanate, tetra-2-ethyl-hexyl titanate, and tetrastearyl titanate.
  • tetraphenyl titanate and other tetraaryl esters are also included.
  • the above alkoxides may be used if the acrylic monomer containing a COOH group is used as the olefinic monomer having crosslinkable groups. It has been found that the adhesives produced using these alkoxides and the acid monomers have excellent strength.
  • the metal alkoxides including the lower alkyl titanates, have the disadvantage of being extremely reactive and have a tendency to gel in combination with the star polymer.
  • the preferred metal alkoxide, chelated metal alkoxide, will solve any stability problems while retaining strength.
  • Chelated esters are not subject to the storage disadvantages discussed above and provide formulated adhesives which can be stored for relatively long periods without substantial increase in viscosity.
  • the chelated metal alkoxides may be used where the olefinic monomer containing the crosslinkable functionality is either an OH or COOH containing monomer to achieve the improved strength and also the vastly improved shrink resistance and stability.
  • the preferred chelated metal alkoxides are chelated aluminum and titanium esters.
  • the chelated titanium esters which are employed in the preferred embodiment of the invention are formed by coordinate bonding between titanium or aluminum and electron donating atoms, such as oxygen or nitrogen.
  • electron donating atoms such as oxygen or nitrogen.
  • the reaction of alkyl esters of titanic acid with amino alcohols, keto alcohols, glycols, or similar polyfunctional alcohols as the ligands, particularly acetyl acetone causes replacement of at least two of the alkoxy groups of the ester with at least two moles of the ligand.
  • Such chelated esters can be formed by various methods, such as by reaction of a tetraalkyl titanate with a glycol, such as 2-ethyl-1 ,3-hexanediol; a diketone, such as 2,4- pentanedione; a hydroxy acid, such as lactic acid, citric acid, or tartaric acid; a keto ester, such as acetoacetic ester; or with an aminoalcohol, such as diethanolamine or triethanolamine.
  • a glycol such as 2-ethyl-1 ,3-hexanediol
  • a diketone such as 2,4- pentanedione
  • a hydroxy acid such as lactic acid, citric acid, or tartaric acid
  • a keto ester such as acetoacetic ester
  • aminoalcohol such as diethanolamine or triethanolamine.
  • chelated aluminum esters examples include aluminum trisacetylacetonate and chelated titanium esters including TYZOR AA and TYZOR GBA, isopropoxy acetylacetonates available from DuPont.
  • the preferred chelated esters employed in the invention are those which are commercially available, which include those formed from octylene glycol, triethanolamine, 2,4-pentanedione, and lactic acid.
  • chelated compounds such as titanium acetylacetonate, when added to the interpolymer solution forms a more stable, latently crosslinkable solution, which upon evaporation of solvent forms a crosslinked polymer matrix.
  • additive materials which do not affect the basic properties of the adhesive. Fillers, tackifiers, antioxidants, stabilizers, and the like are thus sometimes added to the formulated adhesive.
  • the present invention is also directed to a coated article comprising the pressure sensitive adhesive composition of the present invention and also a coated article comprising a pressure sensitive adhesive prepared according to the process of the present invention.
  • the adhesive can be employed in various forms. For instance, it can be cast as a free film interleaved between sheets of release paper and employed in a transfer operation. In other methods of utilization, the adhesive is coated onto a backing member and dried to provide pressure-sensitive adhesive coated materials, such as tapes, sheets or panels. Alternatively, the adhesive may be coated on to a release material and then dried and transferred to a backing member. Cellophane, vinyls, cloth, polyester, rubber, various laminates, and other such flexible materials, as well as wood, metal, hardboard and other less flexible backings, can be coated in this manner.
  • the adhesive of this invention is useful in any application where pressure sensitive adhesives are used. In some cases, the adhesive can be used as a liquid adhesive and applied just prior to use.
  • the dried adhesive composition forms a tacky adhesive which adheres to various substrates to provide a bond of high cohesive strength, thus, making these adhesives especially desirable in uses where holding ability and retention of strength over a period of time are necessary.
  • the shear test is conducted in accordance with PSTC Test Method No. 7.
  • the coating preparation, preconditioning and test conditions are the same as for the peel test.
  • a mixture of acrylates in the ratio of 65 parts 2-ethylhexyl acrylate (“EHA”), 27.5 parts t-octyl acrylamide (“tOA”) and 7.5 parts acrylic acid (“AA”) were polymerized in the presence of 0.65 parts polymercaptan to yield a star polymer.
  • Two different polymercaptans were used, trimethylolpropane tris(3-mercaptopropionate) ("3-arm”), and pentaerythritol tetrakis(3-mercapto-propionate) (“4-amn”).
  • the same monomer composition was polymerized in the presence of a equivalent amount of linear methyl 3-mercaptopropionate to prepare a linear control.
  • the reagents and procedure for preparation of each sample were as described below.
  • the monomer mix was prepared and thoroughly mixed.
  • the initial charge was charged to a 3000 mL reaction flask, equipped with a condenser, paddle stirrer, thermometer, addition funnels and water bath.
  • the initial charge was heated to reflux and held for five minutes.
  • At reflux add very slowly 50% by volume of initiator solution to the flask contents.
  • monomer and initiator were slow added continuously and uniformly over three hours while maintaining reflux.
  • the flask contents were held at reflux for two hours.
  • the contents were cooled to 25°C and analyzed, and the results shown below. Table I
  • the star polymers, samples 1-B, 1- C and 1 -D all have substantially lower viscosity than the linear polymer of same composition at similar polymer concentration of 40%. Additionally the viscosity of the 4-arm radial polymer, sample 1-C, is lower than the 3-arm radial polymer, sample 1-B, at the same polymer concentration.
  • star polymers samples 1-B, 1-C and 1-D, all show good balance of PSA performance and in some cases better than the linear polymer.
  • the monomer mix was prepared and thoroughly mixed.
  • the initial charge was charged to a 3000 mL reaction flask, equipped with a condenser, paddle stirrer, thermometer, addition funnels and water bath.
  • the initial charge was heated to reflux and held for 5 minutes.
  • At reflux add very slowly 50% by volume of initiator solution to the flask contents.
  • monomer and initiator were slow added continuously and uniformly over three hours while maintaining reflux.
  • the flask contents were held at reflux for two hours.
  • the contents were cooled to 25°C and analyzed, and the results shown below.
  • Other monomers and reagents were also prepared by the above method and these results also shown in Table II below.
  • Viscosity, peel, shear and loop tack were plotted against percent acrylic acid, and the results shown in Figures 1-5.
  • Figure 1 indicates that tOA gives the lowest viscosity and that in general, viscosity increases with an increase in acrylic acid content.
  • Figure 2 shows 20 minute peel as a function of acrylic acid content. In general, peel decreases with increase in acrylic acid content, although sometimes a maximum is seen such as with the 106 series containing methyl methacrylate. The steepest decline in peel is seen in the 111 series which contains tOA. However in all cases, peel values are in the range of 20 to 60 oz/inch.
  • Figure 3 shows 24 hour peel, and the tends are exactly the same as in Figure 2, however the peel values are all higher indicating a build up with time.
  • Figure 4 shows loop tack values for all the samples.
  • Figure 5 shows the shear holds for the same polymer.
  • a mixture of acrylates in the ratio of 70 parts 2-ethylhexyl acrylate, 27.5 parts t- octyl acrylamide and 2.5 parts acrylic acid were polymerized in the presence of 0.65 parts tetrafunctional polymercaptan pentaerythritol bis(2-mercaptopropionate) bis(3- mercaptopropionate), to yield a heterocore star polymer.
  • the same monomer composition was polymerized in the presence of equimolarly substituted linear methyl 3-mercaptopropionate to provide a linear control polymer.
  • the reagents and procedure for preparation of each sample were as described below.
  • the monomer mix was prepared and thoroughly mixed.
  • the initial charge was charged to a 3000 mL reaction flask, equipped with a condenser, paddle stirrer, thermometer, addition funnels and water bath.
  • the initial charge was heated to reflux and held for five minutes.
  • At reflux very slowly add 50% by volume of initiator solution to the flask contents.
  • monomer and initiator were slow added continuously and uniformly over three hours while maintaining reflux.
  • the flask contents were held at reflux for two hours.
  • the contents were cooled to 25 C C and analyzed for residual monomers, percent solid, intrinsic viscosity and molecular weight, and the results shown below.
  • thermo mechanical properties of star polymers of the present invention were analyzed by Dynamic Mechanic Analysis ("DMA"). All of these polymers showed a single Tg value.
  • DMA Dynamic Mechanic Analysis
  • star polymers were prepared according to U.S. Patent No. 5,679,762 and analyzed by DMA.
  • the polymers prepared according to the reference showed two Tg values and phase separation.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Organic Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
EP00936446A 2000-06-02 2000-06-02 Anwendung von sternförmigen polymeren in druckempfindlichen klebemitteln Withdrawn EP1290102A1 (de)

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PCT/US2000/015108 WO2001094490A1 (en) 2000-06-02 2000-06-02 The use of star-branched polymers in pressure sensitive adhesives

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