ionace

Ma

ulask

sed foline 2

In this work, metal chelate zirconium acetylacetonate (ZrACA) was added into acrylic polymers with self-adhesiveproperties. These acrylic polymers, known as acrylic pressure-sensitive adhesives (PSA), were crosslinked with ZrACA

long chain molecules conned by crosslinkages into bonding processes are via adhesion and adhering

tack, peel adhesion and shear strength. The rstmeasures the adhesives ability to adhere quickly,the second its ability to resist removal through peel-ing and the third its ability to hold in position whenshear forces are applied [4].

erved.

* Corresponding author. Tel.: +48 60 105 71 12; fax: +48 91483 49 08.

E-mail address: psa_czech@wp.pl (Z. Czech).

European Polymer Journal 42 (

EUROPEANPOLYMER0014-3057/$ - see front matter 2006 Elsevier Ltd. All rights resthree-dimensional networks. They are, in uncross-linked form, capable of sustaining very large revers-ible deformations at low stress. However, a fewtenths of a percent of crosslinking agent make it apressure-sensitive adhesive having viscoelastic uidstate and good mechanical and thermal properties.

Pressure-sensitive adhesives (PSA) are nonmetal-lic materials used to bond other materials, mainlyon their surfaces through adhesion and cohesion[1]. Adhesion and cohesion are phenomena, which

with pressure-sensitive adhesives. The term PSAhas a very precise technical denition and was dealtwith extensively in the chemical literature [3]. Thefunction of PSAs is to ensure instantaneous adhe-sion upon application of a light pressure. Mostapplications further require that they can be easilyremoved from the surface to which they wereapplied, through a light pulling force.

The most importance properties, which are essen-tial in characterizing the nature of PSA comprise:to obtain acrylic self-adhesives with which to study the crosslinking reaction between carboxylic groups of the polymerchain and metal chelate crosslinking agent. 2006 Elsevier Ltd. All rights reserved.

Keywords: Crosslinking of acrylic PSA; Pressure-sensitive adhesives; Acrylic; PSA; Adhesives; Metal chelate zirconium acetylacetonate;Acrylic pressure-sensitive adhesives

1. Introduction

Pressure-sensitive adhesives are composed of

may be described thermodynamically and chemi-cally, but actually they cannot be measured pre-cisely. It was shown [2] that the most importantThe crosslinking reactchelate metal

Zbigniew Czech *,

Szczecin University of Technology, Polymer Institute, K. P

Received 29 November 2005; received in reviAvailable on

Abstractdoi:10.1016/j.eurpolymj.2006.03.022of acrylic PSA usingtylacetonates

rta Wojciechowicz

iego 10, Pl-70-322 Szczecin, Zachodniopomorskie, Poland

rm 9 March 2006; accepted 20 March 20062 May 2006

2006) 21532160

www.elsevier.com/locate/europolj

JOURNAL

2. Methods of crosslinking

The properties of pressure-sensitive adhesivessynthesized by copolymerization of acrylic mono-mers and formulated in organic solvent mixtureare determined, to a great extent, by the kind andquantity of the crosslinking agent added to theself-adhesive. As with molecular weight, crosslink-ing inuences the bulk properties of the lm andbuilds shear, heat and chemical resistance, whilenegatively impacting the tack and peel. It is neces-sary to achieve inter-chain crosslinking for heatresistance, because the pressure-sensitive adhesivepolymers are operating in the region above theirglass transition temperature. Therefore, withoutcrosslinks, the polymer would readily ow underheat, losing all cohesive strength. The crosslinking

carbamates from isocyanates and hydroxyl groupsand the formation of ureas from isocyanates andamines are both well known.

Polymers containing ionic crosslinks such ascarboxylates have been known for many years [8].These ionomers, as they are called, tend to exhibitboth rapid stress relaxation and marked creep underload. Nonetheless, ionic linkages are attractive forcrosslinking in that the reactions can be controlledto achieve the desired properties. If the ionic cross-link is metal mediated, the metal salt might be cho-sen for some particular spectroscopic characteristic.

Past works by Yeh [9] with b-diketonate chelatesof transition metals incorporated in carboxylatedstyreneisoprene (SIR), styrenebutadiene (SBR),and polystyrene rubbers have opened new possibili-ties for identifying crosslinks, estimating crosslink

of cr

2154 Z. Czech, M. Wojciechowicz / European Polymer Journal 42 (2006) 21532160also builds water and chemical resistance, as wellas nal adhesive construction properties to enhancedie cutting, slitting and roll stability [5].

An acrylic copolymer whose chains are onlycrosslinked via hydrogen bonds or inter penetratingsystems (IPN) can hardly be cohesively loaded. Buta few tenths of a percent of crosslinking agent makeit a pressure-sensitive adhesive having goodmechanical and thermal properties.

Traditional methods of crosslinking polymers,which include sulfur vulcanization, peroxide curingand radiation curing, give networks whose crosslinkdensities cannot be examined by simple means [6].

Crosslinking based upon amine, ether, ester oramine bonds located at suitable sites along the poly-mer can be used as both stoichiometry and reactioncan be controlled [7]. For instance, the formation of

Density

Tack

, Adh

esio

n

AdhesionFig. 1. General eects of crosslinkidensity and studying the nature of the chemicalbond in the polymer under varying conditions,using commonly available instrumentation.

With the aid of chemical bonds during the chem-ical crosslinking, an increase in cohesion may beaccomplished during the drying of the PSA coatingin the drying step. Logically, the tackifying proper-ties of the PSA coating, such as tack and adhesion,decrease (Fig. 1) [10].

The transition metals having a coordination num-ber greater than 2, typically 4, 6 or 8 (exemplied byZn, Ni, Mn, Fe, Co, Cr, Al, Ti or Zr), form with 2,4-pentanedione (acetylacetone) chelate complexes [11]known as acetylacetonates. The hydrogen atoms ofthe methylene group CH2 accordingly the induc-tion eect of the neighboring ketone group are verymobile. Therefore, the acetylacetonates show the

osslinkage

Coh

esio

nCohesion

Tackng to the PSA performances.

keto-enol antimerism. The central hydrogen atom ofthe chelate rings is accessible to electrophilic substi-tution [12,13].

The following chelating agents can also be usedas chelating b-diketones: 2-acetylhexanone, 1,3-diphenyl-1,3-propandione, 1-phenyl-1,3-butandione,1,3-diphenyl-1,3-pentandione, 2,4-hexandione, 3,5-heptandione, 3-phenyl-2,4-pentandione, 2,2,6,6-tet-ramethyl-3,5-heptandione or 1,1,1-triuro-2,4-pent-andione [14,15].

The equilibrium between the ketone and enolform of the b-diketone stabilizes slowly at roomtemperature. The two tautomeric forms have beenobserved in IR and NMR spectra [16] (Fig. 2).

Metal chelates that react with the acrylic polymer

Characteristic for crosslinking systems contain-ing metal chelates is the addition of alcohol as a sta-bilizer, after the vaporization of which (in the dryingchannel together with other solvents) the crosslink-ing starts spontaneously. Pressure-sensitive adhesiveacrylics containing the above mentioned crosslink-ing agents are, therefore, called room temperaturecrosslinking pressure-sensitive adhesives [17].

Most of the pressure-sensitive adhesives will ben-et from a short crosslinking time at a temperaturehigher than the volatilization temperature of thepolymerization solvent and the solvent stabilizer.The crosslinking time and temperature will dependupon the particular required acrylate ester mono-mers used, the chelating agent, the optional copoly-

ic fo

Z. Czech, M. Wojciechowicz / European Polymer Journal 42 (2006) 21532160 2155chains containing carboxylic groups are particularlyecient as crosslinking agents; they have the follow-ing formula (Fig. 3).

Chelate-forming reactions are usually exothermicand therefore, the liberated alcohol does not need tobe distilled to make the reaction complete. Indeed,such is the physical nature of the chelates that it isoften more desirable to leave the liberated isopro-panol in the product as a solvent to facilitate han-dling. Only capable of forming coordinate bondswith two donor atoms is metal atom with maximumvalence six. The chelates are therefore manufacturedby adding up to two moles of chelating agent to oneof metal acidester. A typical example is metal che-late titanium acetylacetonate, which is formed byreacting isopropyl titanate with two moles of acetyl-acetone, respectively.

Acetylacetone reacts in its enol form with organicderivatives of Zn, Ni, Mn, Fe, Co, Cr, Al, Ti and Zrto form metal acetylacetonate. This reaction isshown in Fig. 4.

O O O O

H(1) (2a)

Fig. 2. The tautomer

(RO)a

(O)bM

O

O C

CCH

CH3

CH3cFig. 3. General formula of mmerizable comonomer used, if any, the metal chelateused, the volatilization temperature of the reactionby-product after crosslinking, and the requiredend use for the acrylic PSA [18].

Crosslinking of the polymer chains with a view tothe selected composition of functional monomerswill only be aected by the functional carboxylgroups and hydroxyl groups protruding out of thechain. Consequently, the crosslinking agents willreact preferably with the most proton-active-groups, and these are the carboxylic groups of theacrylic acid molecules being connected to the poly-mer chain. Crosslinking relevant for practical appli-cation can only be attained provided that thepolymer chain is equipped with acid groups.

3. Target of the investigations

The target of this work was the investigation ofthe crosslinking mechanism of the acrylic pressure-sensitive adhesives using metal chelate zirconium

O O

H(2b)

O O

H(3)

rms of a b-diketone.

M central metal atoma + b + c = n-metal valenceb = 0 or 1R = alkyl groupetal acetylacetonates.

nium acetylacetonate, aluminum acetylacetonate,f the troups incorporated inthe staization

5. Test methods and instrumentation

Ti

O

O

CH

O CHCH3

CH3

CHCH3CH3

CH3CH3

OCHCH3

CH3+ 2 CH3 C

O

CH C

OH

CH3

acetylacetone (enol form)

CH

CH

CH

e (TiAtitani

2156 Z. Czech, M. Wojciechowicz / European Polymer Journal 42 (2006) 21532160iron acetylacetonate and titanium acetylacetonate,monomers, solvents and AIBN were purchased fromAldrich (Table 1).

The basic solvent-borne pressure-sensitive adhe-acetylacetonate and later the manufacture ofsolvent-borne acrylic pressure-sensitive adhesiveswith high application performances.

4. Starting materials

All starting materials were obtained reagent gradeand were used without further purication unlessotherwise noted. All used crosslinking agents: zirco-

tetraisopropyl titanate

(i-C3H7O)2 TiO

O C

C

titanium acetylacetonat

Fig. 4. Synthesis ofsive was synthesized from 65 wt.% of 2-ethylhexylacrylate, 30 wt.% of methyl acrylate and 5 wt.% ofacrylic acid in the organic solvent ethyl acetate witha boiling point temperature of about 77 C. 2,2-Azo-bis-diisobutyronitrile in the amount of 0.1 wt.% wasused as the thermal initiator to start radical polymer-ization. The nal synthesized solvent-borne basicacrylic pressure-sensitive adhesive was, after addi-tion of isopropyl alcohol stabilizer, characterizedby the following important properties:

Table 1Selected metal chelates

Crosslinkers Chemical formula

Aluminum acetylacetonate (AlACA) Al(C5H7O2)3Titanium acetylacetonate (TiACA) Ti(C5H7O2)2(C3H7O)2Zirconium acetylacetonate (ZrACA) Zr(C5H7O2)4Iron acetylacetonate (FeACA) Fe(C5H7O2)3The inuence of the crosslinking alinking methods is usually determinethe reaction time and to the conceadhesion properties, consideringtack, adhesion, cohesion and shrinthree properties were determinedAFERA (Association des FabricantRubans Auto-Adhesifs) procedurescan be found in AFERA 4015 (t

Appearance Solubility in

Powder Toluene, acetone, ethLiquid Isopropyl alcohol, toPowder Toluene, ethyl alcohoPowder Toluene, acetone, ethpropyl alcohol, after polymer is necessary.ing agents with functional gthe polymer, the addition of bilizer, i.e. iso-Facing the high reactivity o ested crosslink-Polydispersity Pd MW=Mn 1.72Amount of solid materials 45 wt.%Viscosity 4.6 Pa sWeight averagemolecular weight MW

712000 Dalton

Number averagemolecular weight Mn

415000 Dalton

3

3 2

+ 2 i -C3H7OH

CA) isopropanolum acetylacetonate.gents or cross-d in relation tontration versusthe properties:kage. The rstby standard

s Europeens de. Exact detailsack), AFERA

yl acetateluene, ethyl acetatel, acetoneyl alcohol

4001 (peel adhesion) and AFERA 4012 (shearstrength). Administrative address: 60, rue Auber-94408 Vitry Sur Seine Cedex, France.

Shrinkage presents the percentage or millimeterchange of dimensions of the PVC foil covered withPSA after PSA crosslinking and attached to theglass after keeping it 1 week at temperature of70 C. With shrinkage greater than 0.5% or greaterthan 0.5 mm other properties were neglected.

The viscosity of the investigated solvent-borneacrylics pressure-sensitive adhesives was determinedwith a Rheomat RM 189 from Rheometric Scien-tic, with spindle No. 3 at 23 C.

The amount of solid materials was found accord-ing to DIN EN 12092, the residual of monomerswere measured with gas chromatograph Unicam610, J&W DB-1 column, FID detector and integra-tor Unicam 4815.

proceeds only if the polymer chains of PSA containcarboxylic groups as reactive crosslinking centers.The presence of hydroxyl groups does not lead tocrosslinking and gives unsatisfactory cohesionincrease (cohesive failure in the adhesive layer, yetunder a little load).

The crosslinking reaction of acrylic PSA runssimilarly to the reaction between zirconium acetyl-acetonate and the carboxylic group of the acrylicacid, built in the acrylic polymer chain (Fig. 5).

The formation of the zirconium acrylate has beenproven by elementary analysis; the volatile acetylac-etone was identied with the aid of gas chromato-graphy.

In order to explain the crosslinking reaction ofacrylic PSA, by the use of zirconium acetylaceto-nate, the following mechanism of crosslinking pro-cess is to be assumed by the author (Fig. 6).

3

3

som

CH

zir

ium a

Z. Czech, M. Wojciechowicz / European Polymer Journal 42 (2006) 21532160 2157The molecular weight studies were performed intetrahydrofurane with a liquid chromatographLaChrom system: RIDetector L-7490 and LaChromUV Detector L-7400 from Merck-Hitachi, equippedwith a PLgel 106 A column from HewlettPackard.

The volatile by-product acetylacetone was identi-ed with the aid of gas chromatograph Varian CP-3800.

6. Crosslinking mechanism of acrylic PSA usingzirconium acetylacetonate (ZrACA)

Our former examinations [19] proved that thecrosslinking reaction of acrylic pressure-sensitiveadhesives with the aid of metal acetylacetonates

O

O C

CCH

CH3

CH3

Zr

zirconium acetylacetonate

O

O C

CCHZr

+-

CH

CH(1)

me

O

O C

CCH

CH3

CH3 4

+Zr

ZrACA

CH2 CH C

O

OH

acrylic acid

Fig. 5. Reaction between zirconFig. 6. Intramolecular mesomeric stabilizIn the rst step of the crosslinking reaction, thecarboxylic group provided by the acrylic acid unitof PSA copolymer reacts with zirconium acetylacet-onate (with its mesomeric form (2) (Fig. 6)) in thefollowing way (Fig. 7).

In the second stage of the crosslinking reaction ofcarboxylated acrylic PSA the following rearrange-ment proceeds provided by the acyl cation (Fig. 8).

The carbocation acyl cation split o is stabilizedby the p electrons of the oxygen heteroatom. Theoxygen atom interacts with the neighboring electronattracting the cationic centre of the carbon atom,due to its free electron pairs. The formed oxoniumion is unstable, and in the second step of crosslink-ing the following rearrangement proceeds (Fig. 9).

O

O C

CCHZr

+

-

CH3

CH3O

O C

CCHZr

+

-

CH3

CH3(2) (3)

eric stabilization of internal complex

2 CH C

O

O

4

Zr + CH3 C

O

CH2 C

O

CH3

conium acrylate acetylacetone

cetyacetonate and acrylic acid.ation of zirconium acetylacetonate.

OO C

CCHZr

+

-

CH3

CH3

+ H O+ -

C

O

Fig. 7. The rst step of the reaction between ZrAC

O

O C

CCHZr

CH3

CH3

OC

O

Fig. 8. The second step of the reaction between ZrACA and carb

0 1 2 3 4 5 6

t = 25C p = 1.2 bar

Retention time [min]

Sta

rt

ethyl acetate acetylacetone

Fig. 10. Retention peaks of reaction mixture of zirconiumacetylacetonate and acrylic PSA containing carboxylic groups.

O

O C

CCHZr

CH3

CH3

OC

O

H

C

O

O

oxonium-ion zirconium

CH3 C

O

CH C

OH

CH3

acetylacetone(enol-form 85 %)

Fig. 9. The end phase of the reaction between ZrACA with the polyacetylacetone.

2158 Z. Czech, M. Wojciechowicz / European Polymer Journal 42 (2006) 21532160O

O C

CCHZr

CH3

CH3

OC

O

A and carboxylic group of the PSA polymer.

O CCH3OC

O -The acetylacetone by-product formed in the reac-tion between metal acetylacetones and acrylic PSAcontaining acrylic acid carboxylic group has beenidentied by gas chromatography (Fig. 10). Duringthe crosslinking, the acrylic acid was represented bycarboxylic groups available in the acrylic PSA poly-mer chain.

7. Use of metal chelate crosslinking agents after the

polymerization

The solvent-borne acrylic pressure-sensitiveadhesives crosslinkable with metal chelates mustbe stabilized by an addition of alcohols into the

O CCHZr

CH3H

+

oxylic group of the PSA polymer (acyl cation abstraction).

Zr

4

+ CH3 C

O

CH2 C

O

CH3

acrylateacetylacetone

(enol-form)

CH3 C

O

CH2 C

O

CH3

acetylacetone(ketone-form 15 %)

mer chain containing acrylic acid and the tautomeric forms of

ot-life [days]30 40 50

g 1.0t.%

AlACA

FeACA

TiACA

e viscosity of crosslinked acrylic PSA during storage.

0.2 0.4 0.6 0.8 1.0

4

6

8

10

12

14 ZrACA TiACA AlACA FeACA

Tack

[N/2

.5cm

]

Amount of crosslinker [wt.%]

Fig. 12. Tack of various crosslinked acrylic PSA.

18

Z. Czech, M. Wojciechowicz / European Polymer Journal 42 (2006) 21532160 2159polymer solution. The stabilizer has been chosentaking into account to its price and its boiling point.Most often, isopropyl alcohol is used.

The pot-life test has been carried out with anacrylic PSA containing 1.0 wt.% aluminum, tita-nium, iron or zirconium acetylacetonate, stabilizedwith 30 wt.% of isopropyl alcohol (Fig. 11).

As can be seen from Fig. 11 it is very dicult tostabilize the PSA crosslinkable with ZrACA. Thepot-life of such an acrylic adhesive has been nolonger than a few days. The other metal acetyl-acetonates have changed the viscosity of the PSAsolution during the rst 30 days. After one monthof storage time of the best stabilization has beenobserved for acrylic PSAs that contained AlACA

P

Visc

osity

[Pa

s]

0.0

2.5

5.0

7.5

10.5

12.5

15.5

17.5

20.0

22.5

25.0

0 10 20

basic polymer containinand stabilized with 30 w

ZrACA

Fig. 11. Inuence of type of metal chelates on thand TiACA. The conducted tests established thelower reactivity of aluminum acetylacetonate.

The investigated metal chelates have been used inconcentrations of 0.2, 0.4, 0.6, 0.8 and 1.0 wt.% asreferred to the acrylic polymer solids.

The inuence of the tested metal chelates on theperformance characteristics of the acrylic pressure-sensitive adhesive is illustrated in Figs. 1214.

As can be seen from the data of Figs. 1214, theinvestigated metal acetylacetonates with dierentcentral metal atoms are excellent crosslinkingagents, which essentially improve the cohesion ofcrosslinked acrylic pressure-sensitive adhesives.The best values of tack and peel adhesion have beenobserved in the case of zirconium acetylacetonate(ZrACA). The shear strength at 70 C of acrylicadhesives crosslinked with 1.0 wt.% of zirconium,titanium, aluminum and iron acetylacetonate hasbeen measured between 30 and 40 N. wt.% of metal chelate of isopropyl alcoholSummarizing, aluminum and zirconium acetyl-acetonates have turned out to be the best metalchelates as crosslinking agents, useful for industrialcrosslinking of solvent-borne acrylic pressure-sensitive adhesives. The acrylic PSA crosslinked

0.2 0.4 0.6 0.8 1.06

8

10

12

14

16 ZrACA TiACA AlACA FeACA

Peel

adh

esio

n [N

/2.5

cm

]

Amount of crosslinker [wt.%]

Fig. 13. Peel adhesion of various crosslinked acrylic PSA.

2160 Z. Czech, M. Wojciechowicz / European Pwith ZrACA has the advantages of a high tack, highpeel adhesion and moderate shear strength for con-centrations between 0.2 and 0.6 wt.% ZrACA. Theexcellent balance between adhesion and cohesionfor acrylic PSA containing ZrACA is the know-how in the case of industrial use in the areas ofself-adhesive labels and PVC decorative lms.

8. Inuence of investigated crosslinking agent metal

chelates referring to the shrinkage resistance of

solvent-borne acrylic PSA

The target of this investigation was the develop-ment of solvent-borne acrylic PSA for PVC signand marking lms with high performance and lowshrinkage. In this case, the greatest attention wasattached to the shrinkage parameter. With acrylicPSA shrinkage greater than 0.5% other evaluatedPSA properties were neglected.

The inuence of the concentration of the externalcrosslinker metal chelates zirconium acetylacetonate(ZrACA), aluminum acetylacetonate (AlACA), tita-nium acetylacetonate (TiACA) and iron acetyl-

0.2 0.4 0.6 0.8 1.005

1015202530354045 ZrACA

TiACA AlACA FeACA

Shea

r stre

ngth

[N]

Amount of crosslinker [wt.%]

Fig. 14. Shear strength of various crosslinked acrylic PSA.acetonate (FeACA) on shrinkage of the synthesizedsolvent-borne acrylic PSA is described in Fig. 15.

As expected, the amount increase of the testedmetal chelate crosslinking agents ZrACA, AlACA,TiACA and FeACA corresponds with the decreaseof shrinkage of solvent-borne acrylic PSA. By usingZrACA in comparison to AlACA or TiACA aslightly better shrinkage resistance was observed.For this reason the TiACA in PSA technology isbecoming more and more replaced by ZrACA orAlACA as a crosslinker for solvent-borne acrylicPSA. Up to 0.2 wt.% ZrACA or 0.2 wt.% AlACAthe shrinkage values of 0.5% and 0.55% were not sat-isfactory. Above this amount of both metal acetyl-acetonates the shrinkage level dropped under 0.5%.9. Summary

Almost all the properties of tested acrylic PSApresented in this paper show that the mentioned rep-resentatives of the investigated metal chelates aregood alternative crosslinking agents to those usuallyused. This publication can be used by the producerof solvent-borne acrylic pressure-sensitive adhesivesto promote the selected metal chelates as modern,eective crosslinking agents for the future.Especially the fourfunctional zirconium acetylaceto-nate (ZrACA) and threefunctional aluminum acetyl-acetonate (AlACA) guarantee in the PSA technologyseveral excellent properties and the best balance per-formance of crosslinked self-adhesive acrylics.

References

[1] German Industrial Normen DIN 16921.[2] Kohler R. Adhasion 1970;3:90.[3] Satas D. Handbook of pressure sensitive technology. New

York, USA: Van Nostrand Rheinhold Co.; 1982.[4] Everaerts A, Malmer J. WO 93/13148, 1992.[5] Ooka M, Ozawa H. Progr Org Coat 1994;23:3257.

0.0 0.2 0.4 0.6 0.8 1.00.0

0.5

1.0

1.5

2.0

2.5

3.0

ZrACA AlACA TiACA FeACA

Shrin

kage

[%]

Amount of crosslinker [wt.%]

Fig. 15. Shrinkage performances of various crosslinked acrylicPSA.

olymer Journal 42 (2006) 21532160[6] Moore CG, Watson WF. J Polym Sci 1956;19:237.[7] Waish DJ, Allen G, Ballard G. Polymer 1974;15:366.[8] Holliday L. Ionic polymers. NY: John Willey and Sons;

1975.[9] Yeh HC, Ph.D. Thesis, University of Washington, 1982.[10] Czech Z. Crosslinking of acrylic PSA, Ed. TU Szczecin,

1999.[11] Flatau K, Musso H. Angew Chem 1970;82:390.[12] Colmann JP. Angew Chem 1965;77:154.[13] Bock B. Angew Chem 1971;84:239.[14] Labadie JF, Thary C. DE 2525248, 1977.[15] Eisentrager K, Marx M. DE 2134688, 1971.[16] Weidmann B, Seebach D. Angew Chem 1983;95:12.[17] Milker R, Czech Z. Vernetzung von Copolymeren auf

Acrylatbasis, 9. Munchener Klebsto-und Veredelungssem-inar, Munchen, Germany 1984. p. 8591.

[18] Ramesh S, Williams S. WO 96/29318, 1996.[19] Milker R, Czech Z. Polimery 1990;35:32630.

The crosslinking reaction of acrylic PSA using chelate metal acetylacetonatesIntroductionMethods of crosslinkingTarget of the investigationsStarting materialsTest methods and instrumentationCrosslinking mechanism of acrylic PSA using zirconium acetylacetonate (ZrACA)Use of metal chelate crosslinking agents after the polymerizationInfluence of investigated crosslinking agent metal chelates referring to the shrinkage resistance of solvent-borne acrylic PSASummaryReferences