Shear-resistant pressure-sensitive adhesive with high tack

Abstract

Crosslinked pressure-sensitive adhesives (PSAs) based on polymers of branched macromolecules each comprising a main chain and one or more sidechains pendent to the main chain, the constitutional units thereof originating from a) X wt % of one or more acrylic and/or methacrylic esters, with 80<=X<=99.5; b) Y wt % of radically copolymerizable monomers having at least one acid function, with 0.5<=Y<=15; c) Z wt % of vinyl compounds, with 0<=Z<=5, at least one sidechain pendent to the main chain having a number-average molar mass >=1000 g/mol, and the respective amounts of constitutional units originating from a), b) and c) can be the same in each case or differ by not more than 1%, and where a), b) and c) may in each case be the same or different monomers, have detachment properties which can be set independently of one another.

Claims

1. A polymer having a main chain, comprising monomers A), and one or more side chains, comprising macromolecules B), located on the main chain, wherein the constitutional units of the monomers A) and the macromolecules B) are attributable to the following monomers a) X % by weight of one or more acrylic acid esters and/or methacrylic acid esters, wherein 80≦X≦99.5; b) Y % by weight radically copolymerizable monomers having at least one acid function, wherein 0.5≦Y≦15; c) Z % by weight vinyl compounds, wherein 0≦Z≦5 and X+Y+Z is 100, wherein at least one side chain of the one or more side chains located on the main chain has a number-average molar mass of at least 1000 g/mol and the content X, Y and Z of constitutional units attributable to the individual monomers a), b) and c) both in the main chain and in the side chains having a number-average molar mass of at least 1000 g/mol in total is in each case be the same or different, wherein, in the case where the content is different, an upwards or downwards deviation of not more than 1% is present in each case, wherein the monomers a), b) and c) for the main chain and side chains is in each case the same monomers or different monomers.

2. The polymer as claimed in claim 1, wherein 1≦Y≦10.

3. The polymer as claimed in claim 1, wherein the number of side chains having a number-average molar mass of 1000 g/mol or more is between 1 and 5 in the predominant number of macromolecules.

4. The polymer as claimed in claim 1, wherein the number-average molecular weight of the polymer is between 100 000 g/mol and 1 500 000 g/mol.

5. The polymer as claimed in claim 1, wherein there are chosen as monomers a) wholly or predominantly those acrylic acid esters and/or methacrylic acid esters whose homopolymers have a glass transition temperature (differential scanning calorimetry according to DIN 53 765; heating rate 10 K/min) of not more than −10° C.

6. The polymer as claimed in claim 1, wherein there are chosen as monomers a) wholly or predominantly esters of acrylic acid with linear primary alcohols having from 3 to 10 carbon atoms in the alcohol moiety and/or esters of methacrylic acid with linear primary alcohols having more than 8 carbon atoms in the alcohol moiety.

7. The polymer as claimed in claim 1, wherein there are chosen as monomers b) one or more carboxylic acids.

8. The polymer as claimed in claim 7, wherein acrylic acid is chosen as the monomer b).

9. The process for the preparation of a polymer as claimed in claim 1, wherein the amounts X, Y and Z of monomers a), b) and c) for monomer group A and monomer group B are the same.

10. The polymer according to claim 1, further comprising: one or more crosslinker substance present in an amount of from 0.025 to 0.4 by weight based on 100 parts by weight of the polymer to be crosslinked.

11. The polymer according to claim 10, wherein the one or more crosslinker substances are selected from the group consisting of metal chelates, N,N-Diglycidylamines, epoxides and aziridines.

12. The polymer according to claim 10, wherein the one or more crosslinker substances consists of isocyanates present in the amount of from 0.1 to 0.4 part by weight, based on 100 parts by weight of the polymer to be crosslinked.

13. A pressure-sensitive adhesive having a polymer component comprising the polymer according to claim 1, wherein the pressure-sensitive adhesive is crosslinked.

14. The pressure-sensitive adhesive as claimed in claim 13, wherein the polymer component comprises only one or more polymers as claimed in claim 1.

15. The pressure-sensitive adhesive as claimed in claim 13, wherein it is free of resin.

16. A process for the preparation of a polymer as claimed in claim 1, wherein the polymer is produced by free radical polymerization from a monomer group mixture comprising A) W % by weight [based on the monomer mixture comprising monomer groups A) and B)] of the following monomers a) X % by weight [based on monomer group A)] of one or more acrylic acid esters and/or methacrylic acid esters, wherein 80≦X≦99.5; b) Y % by weight [based on monomer group A)] radically copolymerizable monomers having at least one acid function, wherein 0.5≦Y≦15; c) Z % by weight [based on monomer group A)] vinyl compounds, wherein 0≦Z≦5 and B) (100-W) % by weight [based on the monomer mixture comprising monomer groups A) and B)] of the following macromonomers d) macromonomers terminally functionalized by groups containing at least one ethylenic double bond and the number-average molecular weight of which is 1000 g/mol or more and the constitutional units of which are in turn attributable to the monomers a) X % by weight of one or more acrylic acid esters and/or methacrylic acid esters, wherein 80≦X≦99.5; b) Y % by weight radically copolymerizable monomers having at least one acid function, wherein 0.5≦Y≦15; c) Z % by weight vinyl compounds, wherein 0≦Z≦5, wherein 80≦W≦95, wherein the monomers a), b) and c) for monomer group A) and monomer group B) is in each case the same monomers or different monomers, and wherein the amounts X, Y and Z of monomers a), b) and c) for monomer group A) and monomer group B is in each case the same amounts or different amounts, wherein, in the case where the amounts are different amounts, an upwards or downwards deviation of not more than 1% is present in each case.

17. The process for the preparation of a polymer as claimed in claim 16, wherein the monomers a), b) and c) for monomer group A and monomer group B are the same monomers.

Description

EXAMPLES

(1) The invention will be described in greater detail below by means of examples. In addition to the test methods already described above, the following methods are used:

(2) SAF.T.—Shearadhesive Failure Temperature

(3) This test serves to quickly test the shear strength of adhesive tapes under temperature load.

(4) Preparation of the Test Samples:

(5) The adhesive tape sample (pressure-sensitive adhesive coated onto 50 μm PET film) is bonded to a ground steel test plate cleaned with acetone and then rolled six times using a 2 kg steel roller and a speed of 10 m/min. The bonding area of the sample is height×width=13 mm×10 mm, the sample is suspended vertically, protrudes beyond the steel test plate by 2 mm at the upper edge and is strengthened flush with a stable adhesive strip, which serves as support for the distance measuring sensor.

(6) Measurement:

(7) The sample to be measured is loaded at the bottom end with a weight of 50 g. The steel test plate with the bonded sample is heated to the final temperature of 200° C. at a rate of 9° C. per minute, starting at 25° C. The slip distance of the sample is measured by means of a distance measuring sensor in dependence on the temperature and time. The maximum slip distance is set at 1000 μm; if that value is exceeded, the test is terminated. Test climate: room temperature 23±3° C., relative humidity 50±5%.

(8) Positive Test Result:

(9) slip distance after reaching the final temperature (200° C.), in μm.
Negative Test Result: temperature upon reaching the maximum slip distance (1000 μm), in ° C.
Microshear Distance Test (Test B)

(10) This test serves to test the shear strength of adhesive tapes under a temperature load of 40° C.

(11) Preparation of the Test Samples:

(12) As the sample to be tested, a strip of the specimen described above was bonded to a polished, temperature-controlled steel test plate cleaned with acetone and then rolled six times using a 2 kg steel roller and a speed of 10 m/min. The bonding area of the sample was height×width=13 mm×10 mm, the sample was suspended vertically, protruded beyond the steel test plate by 2 mm at the upper edge and was strengthened flush with a stable adhesive strip, which served as support for the distance measuring sensor.

(13) Measurement:

(14) The sample to be measured was loaded at the bottom end with a weight of 100 g. The steel test plate with the bonded sample was heated to 40° C. The deformation of the sample was measured by means of a distance measuring sensor over a period of 15 minutes. The test was carried out at a room temperature of 23±3° C. and a relative humidity of 50±5%.

(15) Tests

(16) The effect obtained by the composition of the polymers according to the invention was investigated in experiments. Examples 1 to 15 describe pressure-sensitive adhesives according to the invention and Examples C16 to C23 describe comparative tests.

(17) Preparation of Macromers

(18) The amounts used for the following reaction can be found in Table 1.

(19) A 0.5-liter glass reactor conventional for radical polymerizations was filled with 2-ethylhexyl acrylate (EHA), optionally acrylic acid (AA) and mercaptoethanol (ME). After nitrogen gas had been passed through for 45 minutes, with stirring, Vazo® 67 (2,2′-azobis(2-methylbutyronitrile, DuPont) was added. The external heating bath was then heated to 75° C. and the reaction was carried out constantly at that external temperature.

(20) After a reaction time of 15 hours, unreacted monomer and 2-mercaptoethanol were removed in vacuo at 120° C. An equimolar amount, relative to the amount of mercaptoethanol used, of methacrylic anhydride was then added. The reaction was carried out for a further 12 hours at a heating bath temperature of 100° C. in order to obtain the oligomer terminal-group-functionalized with an olefinic double bond, the macromonomer. The methacrylic acid formed in the reaction was removed in vacuo at 120° C.

(21) TABLE-US-00001 TABLE 1 2-EHA AA ME Vazo ®67 Methacrylic anhydride 1-3 99 g 1 g 1.72 g 0.53 g 3.40 g 4-6, C23 95 g 5 g 1.83 g 0.53 g 3.61 g 7-9 95 g 5 g 0.91 g 0.53 g 1.80 g 10-12 90 g 10 g  1.96 g 0.53 g 3.87 g 13-15 85 g 15 g  2.09 g 0.53 g 4.13 g C17-C19 100 g  — 1.70 g 0.53 g 3.35 g C20-C22 100 g  — 0.85 g 0.53 g 1.67 g
Preparation of the Comb Polymer

(22) A 2.5-liter glass reactor conventional for radical polymerizations was filled with 2-ethylhexyl acrylate (EHA), acrylic acid (AA) and the respective macromonomer. The amounts can be found in Table 2. 266.7 g of ethyl acetate is then added to the monomer mixture. After nitrogen gas had been passed through for 45 minutes, with stirring, the reactor was heated to 58° C. and 0.2 g of Vazo® 67 was added. The external heating bath was then heated to 70° C. and the reaction was carried out constantly at that temperature. After a reaction time of 1 hour, a further 0.2 g of Vazo® 67 was added. Over a period of 5 hours, the mixture was diluted with in each case from 100 g to 200 g of ethyl acetate hourly, according to the viscosity increase. In order to reduce the residual monomers, 0.6 g of bis-(4-tert-butylcyclohexyl)peroxy dicarbonate was added after 6 hours and after 7 hours, and the mixture was in the meantime diluted with 100 g of ethyl acetate. The reaction was terminated after a reaction time of 24 hours and cooled to room temperature.

(23) TABLE-US-00002 TABLE 2 Test example EHA AA Macromer 1 376.2 g   3.8 g  20 g 2 356.4 g   3.6 g  40 g 3 316.8 g   3.2 g  80 g 4 361 g 19 g 20 g 5 342 g 18 g 40 g 6 304 g 16 g 80 g 7 361 g 19 g 20 g 8 342 g 18 g 40 g 9 304 g 16 g 80 g 10  342 g 38 g 20 g 11  324 g 36 g 40 g 12  288 g 32 g 80 g 13  323 g 57 g 20 g 14  306 g 54 g 40 g 15  272 g 48 g 80 g C16 380 g 20 g  0 g C17 361 g 19 g 20 g C18 342 g 18 g 40 g C19 304 g 16 g 80 g C20 361 g 19 g 20 g C21 342 g 18 g 40 g C22 304 g 16 g 80 g C23 266 g 14 g 120 g 
Results

(24) There were varied the amount of acrylic acid in the polymer and in the macromonomers used, which amount is found again in the polymer as the amount in the side chains (in each case 1, 5, 10 or 15% by weight, based on the polymer or based on the macromonomers used; also lower and higher in the comparative tests); the macromer concentration in the monomer mixture used, which corresponds to the amount (in % by weight) taken up by side chains in the polymer (in each case 5, 10 or 15% by weight, based on the monomer mixture used, in the comparative test also without the use of macromonomer) and the chain length of the macromonomers used.

(25) For the examples according to the invention, it is found that the parameters initial force (“F.sub.max”) and work (“Integral”) behave contrarily (as the macromonomer concentration in the polymer increases, the initial force falls while the detachment work increases). For linear polyacrylates, it is known that with measures which increase the initial force, the total detachment work also increases (for example the addition of suitable resins which increase the adhesive force), while measures that reduce the initial force also reduce the total detachment work. Comparative tests C17 to C19 and C20 to C22 show that a similar trend of initial force and detachment work is to be observed for polymers having side chains that have a number-average molecular weight of more than 2000 g/mol but that do not contain acrylic acid units. The total amount of acrylic acid in the polymer, which here corresponds to Examples 4 to 6 according to the invention, is thus not an adequate condition for the behavior noted according to the invention. It is likewise problematic (again with the same amount of acrylic acid, based on the polymer) when the acrylic acid units are displaced mainly into the side chains:

(26) If the amount of side chains on the polymer molecule becomes too great (if the amount of component b) for introduction of the side chains increases in particular above 20% by weight; see Example C23), then the adhesive forces fall even if the amount of acrylic acid in the main chain and the side chains is distributed equally and is in the range that is advantageous per se, and become too low.

(27) TABLE-US-00003 TABLE 3 Macromer Microshear Amount of Amount of distance Sample AA AA Macromer Elastic tack Test/ total macromer concentration Maximum component SAFT Fmax Integral Example [wt. %].sup.(1) [wt. %].sup.(2) [wt. %].sup.(1) [μm] [%] [° C.] [N] [Nmm] Examples according to the invention (AA in the main and side chain)  1 1 1 5 485 76 155 1.103 0.243  2 1 1 10 412 77 158 1.095 0.269  3 1 1 20 285 79 162 1.082 0.281  4 5 5 5 188 80 165 1.382 0.119  5 5 5 10 174 86 162 1.388 0.148  6 5 5 20 124 85 170 1.241 0.163  7 5 5 5 178 81 165 1.693 0.123  8 5 5 10 165 86 164 1.398 0.158  9 5 5 20 122 86 169 1.245 0.187 10 10 10 5 125 84 180 1.556 0.111 11 10 10 10 112 85 182 1.536 0.118 12 10 10 20 99 85 181 1.513 0.127 13 15 15 5 75 84 >200 1.545 0.112 14 15 15 10 73 86 >200 1.542 0.122 15 15 15 20 71 85 >200 1.541 0.134 Comparative examples C16 5 No macromer 265 79 175 1.474 0.113 C17 5 0 5 311 75 162 1.599 0.115 C18 5 0 10 150 78 169 1.586 0.089 C19 5 0 20 122 86 172 1.364 0.056 C20 5 0 5 231 76 163 1.716 0.117 C21 5 0 10 168 80 167 1.064 0.058 C22 5 0 20 128 85 172 0.644 0.031 C23 5 5 30 99 96 120 0.423 0.031 AA = acrylic acid .sup.(1)based on the total monomer mixture used (monomer groups A + B) .sup.(2)based on the macromonomers used
Characterization of the Macromonomers Used

(28) TABLE-US-00004 TABLE 4 Amount of AA Mn PDI Examples Comonomers [wt. %] [g/mol] [—] 1-3 AA, EHA 1 2800 1.7 4-6, C23 AA, EHA 5 2600 1.5 7-9 AA, EHA 5 5600 1.6 10-12 AA, EHA 10 2600 1.5 13-15 AA, EHA 15 2600 1.8 C17-C19 EHA — 2500 1.5 C20-C22 EHA — 5500 1.7 AA = acrylic acid EHA = 2-ethylhexyl acrylate Mn = number-average molecular weight PDI = polydispersity