PRESSURE SENSITIVE COMPOSITIONS BASED ON A MODIFIED RUBBER POLYMER AQUEOUS DISPERSION

Abstract

The invention relates to an aqueous polymer dispersion which comprises: a) an aqueous polymer dispersion comprising grafted rubber polymeric particles from rubber polymer being selected from natural or synthetic rubber, b) an aqueous polymer dispersion with polymeric particles of a second polymer comprising monomeric units derived from a monomeric composition b) comprising: b1) a (meth)acrylate of a linear or branched alcohol in C.sub.4 to C.sub.10 or a mixture of such (meth)acrylates, said (meth)acrylate having Tg.sub.b1 lower than −30° C., b2) optionally, at least one comonomer having Tg.sub.b2 higher than −30° C.,

with said grafted rubber polymeric particles being grafted in an aqueous dispersion by a part of said monomeric composition b) as defined above. The invention covers also a specific process of preparation of said dispersion, an adhesive composition comprising said dispersion, the use of said dispersion in pressure sensitive adhesives and the resulting adhesive.

Claims

1. An aqueous polymer dispersion comprising a mixture of two aqueous polymer dispersions a) and b) which are different from each other, aqueous polymer dispersion a) comprising grafted rubber polymeric particles a) and aqueous polymer dispersion b) comprising ungrafted polymeric particles b): a) an aqueous polymer dispersion comprising grafted rubber polymeric particles from rubber polymer being selected from natural or synthetic rubber, b) an aqueous polymer dispersion with polymeric particles of a second polymer comprising monomeric units derived from a monomeric composition b) comprising: b1) a (meth)acrylate of a linear or branched alcohol in C.sub.4 to C.sub.10 or a mixture of such (meth)acrylates, said (meth)acrylate having Tg.sub.b1 lower than −30° C., and b2) at least one comonomer having Tg.sub.b2 higher than −30° C., of Tg.sub.b2 higher than −10° C. with said grafted rubber polymeric particles being grafted in an aqueous dispersion by a part of said monomeric composition b) as defined above and with said grafted part of monomeric composition b) on said rubber polymer a) representing from 25 to 50% w/w of the total weight of said monomeric composition b) involved in both grafted polymer particles a) and in ungrafted polymer particles b), wherein b1) is selected from n-butyl acrylate, 2-ethyl hexyl (meth)acrylate, 2-octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl(meth)acrylate or decyl (meth)acrylate or a mixture of at least two or of at least three of these monomers.

2. The aqueous polymer dispersion according to claim 1, wherein said rubber polymer a) is natural rubber.

3. The aqueous polymer dispersion according to claim 1, wherein said rubber polymer a) is synthetic rubber and selected from: polyisoprene and their copolymers, polybutadiene and their copolymers, isoprene-butadiene, and from other copolymers of isoprene and butadiene.

4. The aqueous polymer dispersion according to claim 1, wherein the weight proportion of said rubber polymer a), without grafted monomers, with respect to the global weight of a)+b), represents from 5 to 45%

5. The aqueous polymer dispersion according to claim 1, wherein b1) is 2-ethyl hexyl acrylate.

6. The aqueous polymer dispersion according to claim 1, wherein said polymer b) comprises monomeric units derived from a comonomer b2) selected from: functional and/or non-functional ethylenically unsaturated monomers, with said functional monomers being selected from monomers bearing at least one carboxy (—CO.sub.2H), hydroxyl (—OH), acetoacetoxy, amine or nitrile (—CN) functional group, and with said non-functional monomers being selected from C.sub.1 to C.sub.6 esters of (meth)acrylic acid, vinyl aromatic monomers, and esters of vinyl alcohol with C.sub.2 to C.sub.18 carboxylic acids.

7. The aqueous polymer dispersion according to claim 6, wherein the weight content of b2) in said polymer b) varies from 0.1 to 30%.

8. The aqueous polymer dispersion according to claim 1, wherein said monomeric composition b) comprises 2-ethyl hexyl acrylate as monomer b1) and a comonomer b2) selected from at least one functional or non functional monomer, with said functional monomer selected from monomers bearing at least one carboxy (—CO.sub.2H), hydroxyl (—OH), acetoacetoxy, amine or nitrile (—CN) functional group, and with said non-functional monomers selected from C.sub.1 to C.sub.6 esters of (meth)acrylic acid, vinyl aromatic monomers, and esters of vinyl alcohol with C.sub.2 to C.sub.18 carboxylic acids, with a weight content of 2-ethyl hexyl acrylate as monomer b1) with respect to said monomeric composition b) varying from 70 to 99.9%, of said monomeric composition b) and said polymer b) is a copolymer of 2-ethyl hexyl acrylate as monomer b1) with a comonomer b2) selected from: at least one functional or non functional monomer, with said functional monomer selected from monomers bearing at least one carboxy (—CO.sub.2H), hydroxyl (—OH), acetoacetoxy, amine or nitrile (—CN) functional group, and with said non-functional monomer selected from C.sub.1 to C.sub.6 esters of (meth)acrylic acid, vinyl aromatic monomers, and esters of vinyl alcohol with C.sub.2 to C.sub.18 carboxylic acids, with a weight content of 2-ethyl hexyl acrylate as monomer b1) with respect to said polymer b) varying from 70 to 99.9%.

9. The aqueous polymer dispersion according to claim 1, wherein said comonomer b2) is a functional monomer selected from a monomer bearing at least one carboxy group and/or a monomer bearing at least one hydroxyl group.

10. A process of preparing an aqueous polymer dispersion as defined in claim 1, comprising the following successive steps: i) preparation of an aqueous dispersion of a polymer b) by emulsion polymerization with continuous constant rate feeding in a reactor, of a pre-emulsion of monomers b) comprising b1) and b2), as defined in claim 1, ii) before step iii) as defined below and during said continuous feeding of said pre-emulsion, adjusting of the pH of the reactor at a value higher than 7, by the feeding at a constant feeding rate of an aqueous solution of a basic agent, optionally with said feeding continuing up to the end of the following step iii) or by adding in a shot, an aqueous solution of said basic agent and iii) when the quantity in the reactor of the said continuously fed pre-emulsion of monomers b) represents a prefixed value being from 50 to 85% w/w of said pre-emulsion, then starting a progressive addition at constant feeding rate of an aqueous dispersion of rubber polymer a) as defined according to claim 1 with maintenance of the said continuous feeding at constant rate of the remaining pre-emulsion of monomers b), with a resulting chemical modification of said rubber polymer a) by the grafting reaction of said monomers b) on it, with said emulsion polymerization and grafting reactions being conducted in the presence of an initiator which does not generate acidic decomposition products.

11. The process according to claim 10, wherein the said initiator system is selected from redox initiator systems composed of an organic peroxide including hydroperoxides, and a reducing agent acting as a decomposition activator of said peroxide or from azo initiators.

12. An adhesive composition comprising at least one aqueous dispersion defined according to claim 1.

13. An adhesive composition comprising at least one aqueous dispersion obtained by a process according to claim 10.

14. An adhesive composition according to claim 12, which is a pressure sensitive adhesive (PSA) composition.

15. An adhesive composition according to claim 12, which is a two component composition, said composition further comprising a crosslinking agent selected from polyisocyanates for a comonomer b2) bearing hydroxyl groups and from polyaziridines if the comonomer b2) bears carboxy group.

16. An adhesive composition according to claim 12, wherein it is a pressure sensitive adhesives (PSA) composition for labelling, packaging, assembling, construction and medical applications.

17. An adhesive composition according to claim 14, wherein it is applied in the form of an adhesive tape, an adhesive plastic film, an adhesive label, an adhesive spray or an adhesive coating.

18. An adhesive composition according to claim 17 applied on a substrate selected from: paper, cardboard, wood, plywood, particleboard, metal, glass, plastic, plastic film, composite, textile, fibber, woven fabric, and non-woven fabric.

19. The aqueous dispersion of claim 1, wherein Tg.sub.b1 is lower than −40° C. and Tg.sub.b2 is higher than −10° C.

20. The aqueous dispersion of claim 4, wherein the weight proportion of said rubber polymer a), without grafted monomers, with respect to the global weight of a)+b), represents from 10 to 35%.

21. The aqueous dispersion of claim 8, wherein said comonomer b2) is at least one functional monomer bearing at least one carboxy (—CO.sub.2H) or hydroxyl (—OH) functional group.

22. The aqueous dispersion of claim 8, wherein the said weight content of 2-ethyl hexyl acrylate as monomer b1) with respect to said polymer b) varies from 80 to 98.5%.

Description

EXPERIMENTAL PART

Example 1 (Comparative)

[0070] Production of an Aqueous Polymer Dispersion, without any Rubber Latex (0% of Rubber).

[0071] 866 g of deionized water are added to a glass reactor fitted with a condenser, a stirrer, a temperature control system and inlets for nitrogen, the initiator solutions and the pre-emulsion feed, respectively. A monomer pre-emulsion composed of 981 g of deionized water, 47 g of Rhodocal® DSB, 35 g of Disponil® FES 993, 32.6 g of sodium acetate tri-hydrate, 3887 g of 2-ethyl hexyl acrylate, 168 g of methyl methacrylate, 63 g of acrylic acid and 139 g of hydroxyl ethylacrylate is prepared in another container fitted with a stirrer (pre-emulsifier). When the contents of the reactor have reached a temperature of 50° C., 8 g of 13% tert-butylhydroperoxide solution, 19 mg of ferrous sulphate dissolved in 2 g of deionized water and 23.6 g of 6% Bruggolite® FF6 solution are added into the reactor. About one minute after the addition of initiators, the portion of the monomer pre-emulsion and 101 g of tert-butylhydroperoxide and 206 g of a 6% solution of Bruggolite® FF6 in deionized water are fed into the reactor at a constant feed rate, over a period of 4 hours, taking care to keep the contents of the reactor at a temperature of 60° C. throughout the introduction. After 105 minutes since the start of the monomer pre-emulsion feeding, over a period of 45 minutes, 226 g of 10% sodium hydroxide solution are fed into the reactor. Then, the reaction medium is maintained at 60° C. for a further 15 minutes and 69 g of 13% tert-butylhydroperoxide solution and 183 g of a 6% Bruggolite® FF6 solution are fed separately into the reactor at 60° C. over a period of 100 minutes at constant rate. Half an hour after the end of the above addition, the product obtained is cooled to 35° C. At the end, the mixture is filtered through a screen of 36 mesh. The pH is adjusted with ammonia between 9.0 and 9.5. The dispersion obtained has a pH of 9.4, a viscosity (Brookfield RVT at 20 rpm and at 23° C.) of 450 mPa.Math.s, a dry residue (solids content) of 59.1% by weight (1 h at 105° C.) and a pre-coagulate content on a screen of 275 mesh of about 580 ppm.

Example 2 (Comparative with Physical Mixture with 20.6% of Natural Rubber)

[0072] At 160 g of polymer dispersion of the example 1, are added 40 g of a natural rubber latex (Thay low ammonia grade) with 61.5% solids, viscosity 80 mPa.Math.s at 20 rpm and pH=9.9.

[0073] The mixture here obtained has a pH of 9.5, a viscosity (Brookfield RVT at 20 rpm and at 23° C.) of 3800 mPa.Math.s, a dry residue of 60.1% by weight (1 h at 105° C.) and a pre-coagulate content on a screen of 275 mesh of about 440 ppm.

Example 3 (Comparative Physical Mixture with 30.8% of Natural Rubber)

[0074] At 140 g of polymer dispersion of the example 1, are added 60 g of a natural rubber latex, at pH 9.9 and 61.6% of solids. The mixture here obtained has a pH of 9.7, a viscosity (Brookfield RVT at 20 rpm and at 23° C.) of 3300 mPa.Math.s, a dry residue of 60.1% by weight (1 h at 105° C.) and a pre-coagulate content on a screen of 275 mesh of 481 ppm.

Example 4 (Comparative Physical Mixture with 50% of Natural Rubber)

[0075] At 100 g of polymer dispersion of the example 1, are added 100 g of a natural rubber latex, at pH 9.9 and 61.6% of solids.

[0076] The mixture here obtained has a pH of 9.8, a viscosity (Brookfield RVT at 20 rpm and at 23° C.) of 1780 mPa.Math.s, a dry residue of 60.6% by weight (1 h at 105° C.) and a pre-coagulate content on a screen of 275 mesh of about 835 ppm.

Example 5 (Invention with Hybrid Polymer with 20% of Natural Rubber on Solids)

[0077] 866 g of deionized water are added to a glass reactor fitted with a condenser, a stirrer, a temperature control system and inlets for nitrogen, the initiator solutions and the pre-emulsion feed, respectively. A monomer pre-emulsion composed of 981 g of deionized water, 47 g of Rhodocal® DSB, 35 g of Disponil® FES 993, 32.6 g of sodium acetate tri-hydrate, 3887 g of 2-ethyl hexyl acrylate, 168 g of methyl methacrylate, 63 g of acrylic acid and 139 g of hydroxyl ethylacrylate is prepared in another container fitted with a stirrer (pre-emulsifier). When the contents of the reactor have reached a temperature of 50° C., 8 g of 13% tert-butylhydroperoxide solution, 19 mg of ferrous sulphate dissolved in 2 g of deionized water and 23.6 g of 6% Bruggolite® FF6 solution are added into the reactor. About one minute after having added the initiators, the portion of the monomer pre-emulsion and 101 g of tert-butylhydroperoxide and 206 g of a 6% solution of Bruggolite® FF6 in deionized water are fed into the reactor at a constant feed rate, over a period of 4 hours, taking care to keep the contents of the reactor at a temperature of 60° C. throughout the introduction. After 105 minutes since the start of the monomer pre-emulsion feed, over a period of 45 minutes, 226 g of 10% sodium hydroxide solution are fed into the reactor. When the feed of the sodium hydroxide is ended, 1750 g of natural rubber latex is fed at constant rate over a period of 90 minutes. After 240 minutes since the start of the monomer pre-emulsion feed, all the feeds are ended, then the reaction mass is maintained at 60° C. for a further 15 minutes and 69 g of 13% tert-butyl hydroperoxide solution and 183 g of a 6% Bruggolite® FF6 solution are fed separately into the reactor at 60° C. over a period of 100 minutes at constant rate. Half an hour after the end of the above addition, the product obtained is cooled to 35° C. At the end, the mixture is filtered through a screen of 36 mesh. The dispersion obtained has a pH of 8.7, a viscosity (Brookfield RVT at 20 rpm and at 23° C.) of 392 mPa.Math.s, a dry residue of 59.6% by weight (1 h at 105° C.) and a pre-coagulate content on a screen of 275 mesh of about 190 ppm.

Example 6 (Invention, Hybrid Polymer with 20% of Natural Rubber on Solids, but with Different Grafting Ratio)

[0078] We proceed as in the above disclosed example 5, with the same reactants amounts and global duration of the monomer pre-emulsion feeding at a constant rate over 240 minutes, but the feeding of the NaOH solution start after 150 minutes from the beginning, with a constant rate and a duration of 45 minutes, then start the feed of the same amount of natural rubber of example 5 into the reactor, at constant rate, over the last 45 minutes of the monomer pre-emulsion feed. The dispersion obtained has a pH of 9.3, a viscosity (Brookfield RVT at 20 rpm and at 23° C.) of 600 mPa.Math.s, a dry residue of 58.1% by weight (1 h at 105° C.) and a pre-coagulate content on a screen of 275 mesh of about 250 ppm.

Example 7 (Invention, Hybrid Polymer with 30% of Natural Rubber on Solids)

[0079] We proceed as in above disclosed example 5 but with we feed 2990 g of natural rubber instead of the 1750 g of the example 5. The dispersion obtained has a pH of 9.8, a viscosity (Brookfield RVT at 20 rpm and at 23° C.) of 120 mPa.Math.s, a dry residue of 56.6% by weight (1 h at 105° C.) and a pre-coagulate content on a screen of 275 mesh of about 300 ppm. The polymer dispersion of all the examples were further characterized for their particle size by using a dynamic light scattering coulter N4 plus. From the latex of the previous examples were casted polymer films and on them was determined their glass transition temperatures (Tg) by DSC with a heating rate of 20° C./min. The Tg corresponds to the temperature of the midpoint of the DSC curve, at the third passage (at same heating rate).

[0080] The summary of the characteristics of the polymer dispersions of the examples are reported in Table 1a.

TABLE-US-00001 TABLE 1a FR-AM3343-US-DIV characteristics of the polymer dispersions of the examples dry co- Brookfield agulum viscosity 275 particle % at 20 rpm Solids mesh Tg size Example NR pH (mPa .Math. s) (%) (ppm) (° C.) (nm) Natural 9.9 <200 61.9 150 −62 157 ± 25  rubber (16%) 568 ± 108 (84%) Ex 1 0 9.4 450 59.1 300 −54 422 ±190 (comparative) Ex 2 20 9.5 3800 60.1 440 −53/−62 257 ± 21  (comparative) (28%) 589 ± 43  (72%) Ex 3 30 9.7 3300 60.1 481 −53/−62 359 ± 44  (comparative) Ex 4 50 9.8 1780 60.6 835 −51/−62 457 ± 105 (comparative) Ex 5 20 8.7 392 59.6 190 −58 381 ± 62  (invention) Ex 6 20 9.3 600 58.1 250 −53/−62 374 ± 62  (invention) Ex 7 30 9.8 120 56.6 300 −60 530 ± 129 (invention)

[0081] As it is possible to observe from the Table 1a, all the examples of the present invention show significantly lower viscosities at the same solid content (and same rubber content) than the comparative examples produced by mixing the natural rubber with the acrylic dispersion.

[0082] Moreover, the example 5 shows an amount of dry coagulum lower than any comparative example, meaning that the natural rubber in the process of the present invention does not produce any amount of dry coagulum.

[0083] As observed from the Tg of the polymer films, all polymers of comparative examples produced by mixing the natural rubber with the acrylic dispersion of Example 1 show double Tg corresponding to the two mixed components, meaning that there are 2 separate phases in the polymer film. This observation is contrary to the one from the Tgs of polymers of the examples of the present invention (5, 7), which show a unique Tg, which means a strong inter-diffusion between the two different polymer phases which thus become compatible.

[0084] Among the examples of the invention, only in example 6 when the NR is fed just 45 minutes before the end of the monomer pre-emulsion, it is possible to recognize the two separate Tg, due to a lower amounts of NR grafting. These lower Tg for the adhesives produced with the waterborne dispersions of the present invention, strongly contribute to have a feeling of soft pull, when the label is peeled off from the substrate.

[0085] Table 1b below shows and demonstrates that the latexes of the present invention are stable for a long time even if their pH is lower than 9.

TABLE-US-00002 TABLE 1b Brookfield dry viscosity coagulum particle % at 20 rpm Solids 275 mesh size Example NR pH (mPa .Math. s) (%) (ppm) (nm) Ex 5 after 20 8.5 685 61.7 245 363 ± 68 30 days at 60° C.

Example 8: Application and Characterization of the PSA Polymer Dispersions of the Examples

180 Degree Peel

[0086] Samples of the adhesive either directly coated on Mylar or laminated to Mylar or PP tapes from the release liner were cut in 2.54 cm by about 20 cm test strips. They were rolled down on stainless steel or polypropylene test panels with a 2 kg rubber clad steel roller moving back and forth, ten times, at a rate of about 30 cm/min. After a dwell time of 20 minutes or 24 hours, each test strip was peeled away from the test panel in an Instron Tensile Tester at 180 degrees to the test panel, i.e., folded back on itself and parallel to the surface of the panel, at a rate of about 30 cm/min. The force to remove the adhesive strip from the test panel was measured in Newtons per meter (N/25 mm). Tests were performed in triplicate.

Shear

[0087] Strips of tapes produced in the same way that for the peel test were adhered by its adhesive to a SS plate using a 2 kg rubber clad steel roller with a free end of the tape extending beyond the plate and the adhesive contact area being 2.54 cm×2.54 cm. After the plate was placed at an angle of 2 degrees from the vertical and a load is suspended from the free end. For RT shear, a 1.000 g load was used. The time necessary to drop the load down is the shear time.

Loop

[0088] The ends of the tapes produced were placed into the grips of the dynamometer instrument to form a loop, with the adhesive side down. The specimens were lowered onto a stainless steel/pp panel at a rate of 300 mm/min and then raised at the same rate as tack property was measured by reading the max force to remove the tape from the ss/pp panel. The reported values are an average of 5 measures.

Softness

[0089] The softness of the adhesives is intended as the feeling of a gentle peel or soft pull, without noise and regular speed, when the label is peeled off from the substrate.

[0090] This is a typical characteristic of low Tg adhesives like those produced by using natural rubber. The level of softness of the adhesives is reported with a number from 0 to 5, with 5 we have the higher level of softness equivalent to NR based adhesives.

Rolling Ball

[0091] A rolling ball device, like those described in the PSTC 6 norm (Standard Method), equipped with a standard stainless steel ball of 11 mm ( 7/16″) in diameter are cleaned on all their surfaces with isopropyl alcohol or acetone. Then, the apparatus is placed aligned on a strip of tape produced in the same way that for the peel test, with the adhesives side up, all placed on a surface perfectly horizontal. Therefore, the ball is placed on the upper side of apparatus the release pin, hence the ball is released and allowed to roll down until stop on the adhesive. Measure the distance from the point where the ball initially contacts the adhesive to where the ball stops.

[0092] The 5 measurements average stopping distance in mm is then reported.

Transfer

[0093] The measure of the transfer of adhesives traces is done by applying PP tapes, 25 mm wide, produced with the adhesives of the present invention on stainless steel plates and put in an oven a 40° C. for 2 days, with 1 kg weight on them. After this time, in the oven, the adhesives label is quickly pulled out from the ss plate, if trace of adhesives remain on the ss plate we have a transfer. The absence of transfer of the adhesives has a mark of 5, instead the full transfer of the adhesives has a mark of 0.

[0094] The applicative properties of the adhesives tapes, produced with the waterborne polymer dispersions of the examples are reported in Table 2 below.

[0095] Table 3 presents the results obtained from the waterborne polymer dispersions of the examples crosslinked with 0.5% w/w of polyaziridine applied on PET tapes.

TABLE-US-00003 TABLE 2 Applicative properties of the adhesives on PET tapes Peel ss* Peel ss* Loop 20’ 24 h ss* Shear Rolling % (N/25 (N/25 (N/25 ss* Ball Softness Example NR mm) mm) mm) (h) (mm) 1-5 Ex 1 0 2.3 5.1 4.4 6 120 2 (compar- ative) Ex 2 20 1.2 3.8 4.0 74 50 2 (compar- ative) Ex 4 50 1.0 2.8 3.2 200 50 2 (compar- ative) Ex 5 20 1.5 1.8 5.6 200 35 4 (invention) Ex 6 20 2.2 4.2 4.7 130 45 3 (invention) Ex 7 30 2.2 2.9 3.5 200 35 3 (invention) *ss: on stainless steel

TABLE-US-00004 TABLE 3 Applicative properties of the adhesives, obtained from the waterborne polymer dispersion crosslinked with 0.5% of polyaziridine and applied on PP tapes, instead of a PET film Peel ss Peel ss Loop 20’ 24 h ss (N/25 (N/25 (N/25 Softness Transfer Example % NR mm) mm) mm) 1-5 1-5 Ex 1 0 2.1 2.8 2.9 1 1 (compar- ative) Ex 2 20 1.8 2.2 3.2 2 2 (compar- ative) Ex 4 50 0.9 1.5 3.0 3 3 (compar- ative) Ex 5 20 0.8 1.5 3.0 5 5 (invention) Ex 6 20 1.2 2.2 3.2 3 5 (invention)

[0096] As seen from the results of Table 2, the adhesives obtained with mixture of comparative example 2 shows adhesion a little lower than the adhesion obtained with the dispersion of example 6 (respectively 3.8 vs 4.2) with hybrid polymer and NR fed towards the end of the feed, but with a shear and softness much lower in performances than those obtained with example 6.

[0097] By mixing natural rubber with the polymer dispersion of example 1 to have an adhesive with a shear similar to that of example 6, we need to increase the content of natural rubber up to 50% (example 4), if not using the technology (technical means) of the present invention by producing the hybrid polymer of said aqueous dispersion of the present invention. According to the advantageous solution of the present invention, it needs just only to feed 20% of natural rubber (example 5) during the last step of the emulsion polymerization to obtain the same properties than a mixture with 50% NR. Moreover, all hybrid polymers according to the present invention show (see example 5) a higher degree of softness even if using a lower amount of NR. The adhesives of the present invention when crosslinked with polyaziridine to have removable tape on PET show an improved level of crosslinking, testified by lower peel adhesion when compared with examples 1, 2 and 4, but keeping higher level of softness. Even the transfer resistance is higher for inventive examples 5 and 6 (see Table 3, waterborne polymer dispersions crosslinked with 0.5% of polyaziridine).