FLAME-RETARDANT PRESSURE-SENSITIVE ADHESIVE

Abstract

A pressure-sensitive adhesive having good adhesive and flame retardancy properties is provided. The pressure-sensitive adhesive comprises: (A) at least one poly(meth)acrylate and (B) at least one organophosphorus compound, wherein the monomer composition forming the basis for the poly(meth)acrylate comprises (i) at least one (meth)acrylic ester whose alcohol component contains more than 4 carbons; (ii) at least one (meth)acrylic ester whose alcohol component contains not more than 4 carbons; and (iii) acrylic acid and/or methacrylic acid at a total of at least 5 wt %. Also provided is a method of using the pressure-sensitive adhesive as a flame-retardant pressure-sensitive adhesive.

Claims

1. Pressure-sensitive adhesive comprising: at least one poly(meth)acrylate; and at least one organophosphorus compound; wherein the monomer composition forming the basis for the poly(meth)acrylate comprises at least one (meth)acrylic ester whose alcohol component contains more than 4 carbons; at least one (meth)acrylic ester whose alcohol component contains not more than 4 carbons; and acrylic acid and/or methacrylic acid at a total of at least 5 wt %.

2. Pressure-sensitive adhesive according to claim 1, wherein the glass transition temperature of the poly(meth)acrylate by test method A is <0° C.

3. Pressure-sensitive adhesive according to claim 1, wherein the at least one (meth)acrylic ester whose alcohol component contains more than 4 carbon atoms is present in the monomer composition forming the basis for the poly(meth)acrylate at a total of 50 to 90 wt %.

4. Pressure-sensitive adhesive according to claim 1, wherein the at least one (meth)acrylic ester whose alcohol component contains not more than 4 carbons is present in the monomer composition forming the basis for the poly(meth)acrylate at a total of 10 to 40 wt %.

5. Pressure-sensitive adhesive according to claim 1, wherein the monomer composition forming the basis for the poly(meth)acrylate comprises methyl acrylate at more than 15 wt %.

6. Pressure-sensitive adhesive according to claim 1, wherein the pressure-sensitive adhesive comprises organophosphorus compounds at a total of at least 15 wt %, based on a total weight of the pressure-sensitive adhesive.

7. Pressure-sensitive adhesive according to claim 1, wherein the organophosphorus compound is an aromatic organophosphorus compound.

8. Pressure-sensitive adhesive according to claim 1, wherein the organophosphorus compound is a bisphenol A bis(diphenyl phosphate).

9. Pressure-sensitive adhesive according to claim 1, wherein the pressure-sensitive adhesive comprises at least one rosin ester.

10. Pressure-sensitive adhesive according to claim 9, wherein the rosin ester is a pentaerythritol rosin ester.

11. Pressure-sensitive adhesive according to claim 1, wherein the pressure-sensitive adhesive comprises at least one iminophosphorane.

12. Pressure-sensitive adhesive according to claim 1, wherein the pressure-sensitive adhesive comprises at least one amine, and optionally additionally at least one iminophosphorane.

13. A method comprising adhesive bonding of at least one substrate with a flame-retardant pressure-sensitive adhesive, wherein the flame-retardant pressure-sensitive adhesive is the pressure-sensitive adhesive according to claim 1.

Description

EXAMPLES

[0074] Raw materials used: [0075] Butyl acrylate: CAS number 141-32-2 [0076] Ethylhexyl acrylate: CAS number 103-11-7 [0077] Methyl acrylate: CAS number 96-33-3 [0078] Acrylic acid: CAS number 79-10-7 [0079] Vazo 67: 2,2′-Azodi(2-methylbutyronitrile), CAS number 13472-08-7, Akzo Nobel [0080] Perkadox 16: Bis(4-tert-butylcyclohexanyl) peroxydicarbonate, CAS number 15520-11-3, Akzo Nobel [0081] Dertophene T 105: Terpene-phenolic resin, softening point around 105° C.; MW˜850 g/mol; DRT [0082] Foral 105 E: Hydrogenated pentaerythritol rosin ester, softening point around 100° C.; MW˜1002 g/mol; Eastman [0083] Erisys GA 240: N,N,N′,N′-Tetrakis(2,3-epoxypropyl)-m-xylene-α,α′-diamine, Emerald Performance Materials [0084] GC-BDP: Bisphenol A bis(diphenylphosphate), CAS number 5945-33-5; GREENCHEMICALS SPA [0085] GC-TPP: Triphenyl phosphate, CAS number 115-86-6; GREENCHEMICALS SPA [0086] NORD-MIN RDP: Tetraphenyl-m-phenylenebis(phosphate) (resorcinol bis(diphenyl phosphate)), CAS number 57583-54-7; Nordmann [0087] Rabitie FP 110: Phenoxyphosphazene; Fushimi Pharmaceutical Co., Ltd. [0088] Flamestab NOR 116 FF: CAS number 191680-81-6; BASF SE

Preparation of the Polyacrylates

[0089] Polyacrylate 1

[0090] A conventional 2 L glass reactor suitable for radical polymerizations with evaporative cooling was charged with 300 g of a monomer mixture composed of 201 g of n-butyl acrylate, 90 g of 2-ethylhexyl acrylate and 9 g of acrylic acid and also with 200 g of acetone: special-boiling-point spirit 60/95 (1:1). After nitrogen gas had been passed through the reactor for 45 minutes with stirring, the reactor was heated to 58° C. and 0.15 g of 2,2′-azodi(2-methylbutyronitile (Vazo 67®, Akzo Nobel) in solution in 6 g of acetone was added. The external heating bath was then heated to 75° C. and the reaction was carried out constantly at this external temperature. After a reaction time of 1 h a further 0.15 g of Vazo 67®, in solution in 6 g of acetone, was added. After 3 hours the batch was diluted with 90 g of special-boiling-point spirit 60/95.

[0091] After a reaction time of 5 h 30 min, 0.45 g of bis(4-tert-butylcyclohexanyl) peroxydicarbonate (Perkadox 16®, Akzo Nobel) in solution in 9 g of acetone was added. After a reaction time of 7 hours, a further 0.45 g of bis(4-tert-butylcyclohexanyl) peroxydicarbonate (Perkadox 16®, Akzo Nobel), in solution in 9 g of acetone, was added. After a reaction time of 10 hours, the batch was diluted with 90 g of special-boiling-point spirit 60/95. After a reaction time of 24 h, the reaction was terminated and the batch was cooled to room temperature.

[0092] The resultant polyacrylate 1 has a glass transition temperature (T.sub.g) by test method A of −46° C.

[0093] Polyacrylate 2

[0094] A conventional 2 L glass reactor suitable for radical polymerizations with evaporative cooling was charged with 300 g of a monomer mixture composed of 219 g of 2-ethylhexyl acrylate, 60 g of methyl acrylate and 21 g of acrylic acid and also with 200 g of acetone: special-boiling-point spirit 60/95 (1:1). After nitrogen gas had been passed through the reactor for 45 minutes with stirring, the reactor was heated to 58° C. and 0.15 g of 2,2′-azodi(2-methylbutyronitrile (Vazo 67®, Akzo Nobel) in solution in 6 g of acetone was added. The external heating bath was then heated to 75° C. and the reaction was carried out constantly at this external temperature. After a reaction time of 1 h a further 0.15 g of Vazo 67®, in solution in 6 g of acetone, was added. After 3 hours the batch was diluted with 90 g of special-boiling-point spirit 60/95.

[0095] After a reaction time of 5 h 30 min, 0.45 g of bis(4-tert-butylcyclohexanyl) peroxydicarbonate (Perkadox 16®, Akzo Nobel) in solution in 9 g of acetone was added. After a reaction time of 7 hours, a further 0.45 g of bis(4-tert-butylcyclohexanyl) peroxydicarbonate (Perkadox 16®, Akzo Nobel), in solution in 9 g of acetone, was added. After a reaction time of 10 hours, the batch was diluted with 90 g of special-boiling-point spirit 60/95. After a reaction time of 24 h, the reaction was terminated and the batch was cooled to room temperature.

[0096] The resultant polyacrylate 2 has a glass transition temperature (T.sub.g) by test method A of about −34° C.

[0097] Production of the Pressure-Sensitive Adhesives:

Example 1

[0098] The terpene-phenolic resin Dertophene T 105 was dissolved in the solution of the polyacrylate 1 in a weight ratio of 70:30, based on the polymer solids content. Bisphenol A diphenyl phosphate was added to this solution, giving a 30% mass fraction of solids in the mixture. The mixture was then diluted with acetone, to reach a final solids content of 38%. The mixture was placed on a roller bed until a homogeneous solution had formed (around 12 h). Thereafter a crosslinker solution (3 wt % Erysis GA 240 in acetone) was added at 0.075 part by weight, based on 100 parts by weight of polymer, and the adhesive was coated in a thickness of 100 μm onto a siliconized film, using a bar coater on a laboratory coating bench. The coatings were subsequently dried at 120° C. for 15 min.

Examples 2-9

[0099] The procedure in each case was as in Example 1. The composition of the adhesives is reported in Table 1.

[0100] Production of the Test Specimens:

[0101] For the tests, the adhesive was laminated with a trichloroacetic acid-etched PET film 23 μm thick. The adhesive-free side of the film additionally had a layer of adhesive 100 μm thick laminated to it, to produce a double-sided tape.

[0102] Test Methods:

[0103] Peel Adhesion

[0104] The peel adhesion to CRES steel was determined under testing conditions of 23° C.+/−1° C. temperature and 50%+/−5% relative humidity.

[0105] A strip of the adhesive tape specimen 20 mm wide was applied to steel plates which beforehand had been washed twice with acetone and once with isopropanol and left thereafter to lie in the air for 5 minutes to allow the solvent to evaporate. The pressure-sensitive adhesive strip was pressed onto the substrate twice with an applied pressure corresponding to a weight of 2 kg. The adhesive tape was subsequently peeled from the substrate immediately at an angle of 90° and at a velocity of 300 mm/min. The results of measurement are reported in N/cm as an average from three measurements.

[0106] Static Shear Test

[0107] The shear strength was determined under testing conditions of 23° C.+/−1° C. temperature and 50%+/−5% relative humidity.

[0108] The test specimens were trimmed to a width of 13±0.2 mm and stored under the conditions for at least 16 h. Testing took place using 50×25 mm ASTM steel plates with a thickness of 2 mm and with a 20 mm marking line, these plates, prior to bonding, having been cleaned intensely with acetone a number of times and left thereafter to dry for 1-10 min. The bond area was 13×20±0.2 mm. The test strips were applied in longitudinal direction centrally to the substrate, avoiding air inclusions by running over them with the finger or using a suitable wiping device, application taking place such that the top edge of the test specimen lay precisely at the 20 mm marking line.

[0109] Because the specimens tested were double-sided, the reverse side was taped off with aluminium foil. The freely protruding end was taped off with paper or a sheet of card. The adhesive strip was then rolled down back and forth 2 times with a 2 kg roller. After it had been rolled down, a belt loop (weight 5-7 g) was attached on the protruding end of the adhesive tape.

[0110] An adapter plaque was then mounted on the front side of the shear test plate with a screw and nut. In order to ensure a secure seating of the adapter plaque on the plate, the bolt was tightened forcefully by hand.

[0111] The plate thus prepared was mounted by means of the adapter plaque on a clock counter by means of a hook; a 1 kg weight was then suspended smoothly in the belt loop.

[0112] The adhesion time between rolling down and loading was 12 min. Measurements were made of the time in minutes until the bond fails; the results of measurement are on average from three measurements.

[0113] 12 s Vertical Bunsen Burner Test

[0114] The 12 s vertical Bunsen burner test is carried out according to FAR 25.853 (Appendix F Part I (a)(1)(II)): The sample is held in a vertical position in a U-frame, with the sample hanging free, in other words without being bonded on a substrate, and a Bunsen burner flame is applied from below for 12 s. When the flaming time of 12 s has elapsed, the burner is removed and the material is observed. The following parameters are documented:

[0115] a) average afterburn time: time in s for which the sample burns after the burner flame has been removed;

[0116] b) average drop burning time: time in s for which the burning material continues to burn after having dropped from the sample;

[0117] c) average burning length: distance from the initial sample edge to the most remote point at which the sample has undergone damage.

[0118] At least 3 test specimens were tested.

[0119] The specimens are considered to be flame retardant if they complied with the requirements below in accordance with the FAR 25.853 standard (Appendix F Part I (a)(1)(II)):

[0120] Average afterburn time: <15 s

[0121] Average drop burn time: <5 s

[0122] Average burning length: <203.2 mm.

[0123] The results of tests are contained in Table 1.

TABLE-US-00001 TABLE 1 Compositions of the examples and results Example No. Composition 1 (comp.) 2 3 4 5 6 7 8 9 Polyacrylate 1   49% Polyacrylate 2   49%   49%   49% 55.3% 55.3% 55.3% 55.3% 55.3% Dertophene T 105   21%   21% Foral 105-E   21%   21% 23.7% 23.7% 23.7% Foral 85-E 23.7% Foral AX 23.7% Bisphenol A   30%   30%   30%   20%   20%   20%   20% bis(diphenylphosphate) Resorcinol bis(diphenyl   20% phosphate) Triphenyl phosphate   20% Rabitle FP 110   10% Flamestab NOR 116 FF   1%   1%   1%   1%   1% Erysis GA 240 0.04% 0.04% 0.04% 0.04% 0.04% 0.04% 0.04% 0.04% 0.04% Example No. 1 2 3 4 5 6 7 8 9 Peel adhesion 90° CRES 7.2 12.9 10.5 11.0 12.0 5.6 5.1 3 4.4 [N/cm] Holding power RT [min] 633 3312 2888 4595 7213 2140 1532 718 6878 Burning length [mm] 213 175 165 78 25 75 200 28 62 Afterburn time [s] 0 14 7 0 0 0 8.4 0 0 Afterburn time, drop [s] 0 0 1 0 0 1 1 0 0 Sooting Yes Yes No No No No No No No