PERMANENTLY TACKY ADHESIVES WITH IMPROVED ENVIRONMENTAL COMPATIBILITY

Abstract

The invention provides resin- and mineral oil-free pressure-sensitive adhesive compositions, comprising 55%-100% by weight of a copolymer of propylene and one or more further monomers selected from the group composed of ethylene and 1-olefins having 4 to 20 carbon atoms, wherein the copolymer has been prepared with the aid of metallocene catalysts and is characterized by a. a melt viscosity at 170° C. of 20 to 8000 mPas (DIN 53019); b. a density of 0.84 to 0.90 g/cm.sup.3 (23° C., ISO 1183); c. a glass transition temperature of less than −30° C. (DIN EN ISO 11357-2:2014); and d. a flow point, measured according to ASTM D97, of less than 50° C.,
which due to their permanently tacky properties are suitable as pressure-activated pressure-sensitive adhesives.

Claims

1. A resin- and mineral oil-free pressure-sensitive adhesive composition, comprising 55%-99% by weight of a copolymer of propylene and one or more further monomers selected from the group composed of ethylene and 1-olefins having 4 to 20 carbon atoms, wherein the copolymer has been prepared with the aid of metallocene catalysts and has a melt viscosity at 170° C. of 20 to 8000 mPas (DIN 53019), a density of 0.84 to 0.90 g/cm.sup.3 (23° C., ISO 1183), a glass transition temperature of less than −30° C. (DIN EN ISO 11357-2:2014), a flow point, measured according to ASTM D97, of less than 50° C., and wherein a further polymer may optionally be present in the pressure-sensitive adhesive composition.

2. The pressure-sensitive adhesive composition as claimed in claim 1, wherein the copolymer has an enthalpy of fusion, measured according to ISO 11357-2, of 0-50 J/g.

3. The pressure-sensitive adhesive composition as claimed in claim 1, comprising 55%-99% by weight of a copolymer of propylene and 1%-45% by weight of at least one further polymer selected from the group of further polyolefins, of waxes, of natural or synthetic rubbers, of polyacrylates, of polyesters, of polychloroprenes, of polyvinyl ethers or of polyurethanes.

4. The pressure-sensitive adhesive composition as claimed in claim 3, wherein the at least one further polymer is at least one further polyolefin.

5. The pressure-sensitive adhesive composition as claimed in claim 4, wherein the further polyolefin has a glass transition temperature of less than −15° C. (DIN EN ISO 11357-2:2014), a melt viscosity at 170° C. of less than 50 000 mPas (DIN 53019) and a flow point of greater than 50° C. (ASTM D97).

6. The pressure-sensitive adhesive composition as claimed in claim 1, wherein the pressure-sensitive adhesive composition has a Dahlquist criterion of G″105 Pa at 25° C. and 1 Hz.

7. The pressure-sensitive adhesive composition as claimed in claim 1, wherein the copolymer of propylene is derived from 70%-95% by weight of propylene and from 5%-30% by weight of ethylene.

8. The pressure-sensitive adhesive composition as claimed in claim 1, wherein the copolymer of propylene has a melt viscosity at 170° C. (DIN 53019) of 30 to 5000 mPas.

9. The pressure-sensitive adhesive composition as claimed in claim 1, wherein the copolymer of propylene has a glass transition temperature, measured according to DIN EN ISO 11357-2:2014, of less than −35° C.

10. The pressure-sensitive adhesive composition as claimed in claim 1, wherein the copolymer of propylene has a flow point, measured according to ASTM D97, of less than 40° C.

11. The pressure-sensitive adhesive composition as claimed in claim 1, wherein the pressure-sensitive adhesive composition contains organic or inorganic pigments, fillers, flame retardants, stabilizers, antistats, antioxidants and light stabilizers.

12. The pressure-sensitive adhesive composition as claimed in claim 1, wherein the copolymer of propylene has undergone polar modification.

13. The use of a pressure-sensitive adhesive composition as claimed in claim 1 for the joining of substrates.

14. The use of a pressure-sensitive adhesive composition as claimed in claim 13 for the joining of a substrate with a surface energy of less than 35 mN/m, preferably of less than 25 mN/m, with one or more substrates with any surface energy.

15. The use of a pressure-sensitive adhesive composition as claimed in claim 14 for the joining of a substrate made from Teflon, or of a substrate having a siliconized surface, with one or more substrates with any surface energy.

16. The pressure-sensitive adhesive composition as claimed in claim 2, wherein the enthalpy of fusion, measured according to ISO 11357-2, is 0-30 J/g.

17. The pressure-sensitive adhesive composition as claimed in claim 16, wherein the enthalpy of fusion, measured according to ISO 11357-2, is 0-20 J/g.

18. The pressure-sensitive adhesive composition as claimed in claim 8, wherein the melt viscosity at 170° C. (DIN 53019) is 50 to 3000 mPas.

19. The pressure-sensitive adhesive composition as claimed in claim 9, wherein the glass transition temperature, measured according to DIN EN ISO 11357-2:2014, is less than −40° C.

Description

EXAMPLE 1

[0054] Preparation of a Propylene-Ethylene Copolymer According to the Invention (in Accordance with EP 0384264A1, Examples 1-16).

[0055] A dry 16 dm.sup.3 tank was flushed with nitrogen and filled with 50 dm.sup.3 (corresponding to 3.1 bar) of hydrogen and with 10 dm.sup.3 of liquid propylene. Then, 30 cm.sup.3 of toluenic methylaluminoxane solution (corresponding to 40 mmol of Al, average degree of oligomerization of the methylaluminoxane n=20) and 100 g of ethylene were added and the mixture was stirred for 15 minutes at 30° C.

[0056] At the same time, 8.0 mg of the metallocene dimethylsilylbis-1-indenylzirconium dichloride were dissolved in 15 cm.sup.3 of toluenic methylaluminoxane solution (20 mmol of Al) and pre-activated by leaving to stand for 15 minutes. The orange-red solution was added to the tank. The polymerization system was heated to 80° C. and maintained at this temperature during the polymerization time (60 min) by appropriate cooling. A further 330 g of ethylene were metered in steadily during the polymerization time.

[0057] The propylene-ethylene copolymer obtained (yield 1.95 kg) had a propylene content of 79.5% by weight. Determination was effected by .sup.13C NMR spectroscopy in accordance with Ser van der Ven, Polypropylene and other Polyolefins, chap. 13, p. 568f, Amsterdam, Oxford, New York, Tokyo 1990. The copolymer exhibited the following indices:

[0058] Melt viscosity at 170° C.: 210 mPas (DIN 53019)

[0059] Density at 23° C.: 0.85 g/cm.sup.3 (ISO 1183)

[0060] Glass transition temperature: −48° C. (DIN EN ISO 11357-2:2014)

[0061] Enthalpy of fusion: 0 J/g (ISO 11357-3)

[0062] Flow point: 24° C. (ASTM D97)

EXAMPLE 2

[0063] A dry 50 dm.sup.3 tank was flushed with nitrogen and filled with 9 dm.sup.3 of isohexane, 11.9 dm.sup.3 of hydrogen (corresponding to 530 mmol) and also 1.4 dm.sup.3 of propylene and 140 cm.sup.3 of ethylene.

[0064] At the same time, 5.2 mg of the metallocene dimethylsilylbis-1-indenylzirconium dichloride were dissolved in 5 cm.sup.3 of toluenic methylaluminoxane solution (20 mmol of Al) and pre-activated by leaving to stand for 15 minutes. The orange-red solution was added to the tank. The polymerization system was heated to 105° C. and maintained at this temperature during the polymerization time (60 min) by appropriate cooling. A further 200 g of ethylene were metered in steadily during the polymerization time.

[0065] The propylene-ethylene copolymer obtained (yield 2.9 kg) had a propylene content of 87.1% by weight. Determination was effected by .sup.13C NMR spectroscopy in accordance with Ser van der Ven, Polypropylene and other Polyolefins, chap. 13, p. 568f, Amsterdam, Oxford, New York, Tokyo 1990. The copolymer exhibited the following indices:

[0066] Melt viscosity at 170° C.: 4500 mPa.Math.s (DIN 53019)

[0067] Density at 23° C.: 0.86 g/cm.sup.3 (ISO 1183)

[0068] Glass transition temperature: −38° C. (DIN EN ISO 11357-2:2014)

[0069] Enthalpy of fusion: 10 J/g (ISO 11357-3)

[0070] Flow point: 45° C. (ASTM D97)

[0071] Melt mixtures of the components were prepared by homogeneous stirring at 170° C. according to tables 1 and 2 and the melt viscosity and density of the resulting pressure-sensitive adhesive composition were determined. Resins available under the trade names Regalite®, Sukorez® (Kolon), Kristalex®, Eastotac®, Piccotac® (Eastman Chemical Company) or Escorez® (Exxon Mobil) were used in the comparative formulations.

[0072] The adhesive effect of the hot-melt adhesive composition according to the invention was determined qualitatively in various experiments.

[0073] This involved applying the pressure-sensitive adhesive composition according to the invention to a substrate by melting and homogenizing the materials at 200° C. and subsequently applying (knife coating) at 180° C. After 24 h this substrate thus-coated was adhesively bonded to a second substrate made of the same or of a different material by pressing together the faces to be joined. After a waiting time of 5 min, the pressure-sensitive adhesive properties were assessed by separating the two substrates from each other again. A distinction was made in this case as to whether the adhesive bond [0074] a) was adhesively separable (A) (i.e. the adhesive connection is separated at the substrate face) or [0075] b) was cohesively separable (C) (i.e. the adhesive connection is separated within the adhesive phase and adhesive residues remain on both substrate faces), or [0076] c) whether there was material failure (M) signifying destruction of the substrate before the adhesive connection is separated, that is to say the adhesive connection is cohesively and adhesively stronger than the substrates. [0077] d) If no pressure-activated adhesive bonding was possible because the pressure-sensitive adhesive composition could not be activated by gentle application of pressure with the thumb, then the designation (D) was assigned.

[0078] In addition, the tack of the pressure-sensitive adhesive composition was evaluated by tactile comparison and was divided into the following categories: a) marked, aggressive; b) barely distinct; c) not present.

[0079] The open time was determined by melting and homogenizing the materials at 200° C. The mixture is applied (knife coated) to cardboard at 180° C. and a cardboard strip is stuck on every 5 s by application of pressure with the thumb. This process is repeated until the cardboard no longer sticks or only sticks slightly. The time measured from application until the cardboard no longer sticks is the open time.

TABLE-US-00001 TABLE 1 Application examples (according to the invention)/(use amounts in % by weight) AE 1 AE 2 AE 3 AE 4 AE 5 AE 6 AE 7 AE 8 AE 9 AE 10 AE 11 Polyolefin (inv. 1) 75 70 50 65 65 80 90 100 Polyolefin (inv. 2) 100 70 50 Versify 4301 15 20 20 20 20 10 30 Vestoplast 703 10 Vestoplast 828 10 Eastoflex 1060 50 15 50 Vestoplast 608 15 Viscosity @170° C. 1814 7332 1673 5025 4721 3606 862 200 8120 7200 8100 [mPa .Math. s] Density [g/cm.sup.3] 0.854 0.853 0.857 0.853 0.854 0.854 0.854 0.851 0.85 0.858 0.854 Dahlquist crit. yes yes yes yes yes yes yes yes yes yes yes satisfied Open time Endless Endless Endless Endless Endless Endless Endless Endless Endless Endless Endless Adhesive prop. A A C A A C C C C A C Glass/PET Adhesive prop. C C C C C C C C C C C PP/PP Adhesive prop. C C C C C C C C C C C PE/PE Adhesive prop. M M M M M M M M M M M Paper/paper Adhesive prop. M C C C C M M C M M C Silicone paper/ silicone paper Tack a a a a a a a a a a a Assessment of adhesive bonding: A) adhesively separable C) cohesively separable M) material failure D) no pressure-activated adhesive bonding possible. Assessment of tack: a) marked, aggressive b) barely distinct c) not present.

TABLE-US-00002 TABLE 2 Comparative examples (not according to the invention)/(use amounts in % by weight) CE1 CE2 CE3 CE4 CE5 CE6 CE7 Polyolefin (inv. 1) 45 45 45 70 55 Polyolefin (inv. 2) 45 70 Versify 4200 30 30 Versify 4301 30 15 15 15 Vistamaxx 6502 30 Regalite 1100 25 25 25 25 Sukorez SU 100 15 15 30 Viscosity @170° C. 17 230    17 953    12 357    10 023    120 000    40 000    7000 (@150° C.) [mPa .Math. s] Density [g/cm.sup.3]    0.882    0.884    0.882    0.871    0.885    0.872 not known Dahlquist criterion no no no no no no no satisfied Open time [s] 45 30 95 60 120  135  140  Adhesive prop. D D D D D D D Glass/PET Adhesive prop. D D D D D D D PP/PP Adhesive prop. D D D D D D D PE/PE Adhesive prop. D D D D D D D Paper/paper Adhesive prop. D D D D D D D Silicone paper/ silicone paper Tack c c c c c c c Assessment of adhesive bonding: A) adhesively separable C) cohesively separable M) material failure D) no pressure-activated adhesive bonding possible. Assessment of tack: a) marked, aggressive b) barely distinct c) not present.

[0080] The examples according to the invention showed that identical or different substrates can be reversibly adhesively bonded with the aid of the pressure-sensitive adhesive composition according to the invention and that the adhesive connection can be separated either adhesively or cohesively without a resin or plasticizer needing to be used. These properties can be exploited when producing pressure-sensitive adhesive connections as for example are necessary for use in foodstuff packagings, diapers, female hygiene products and medical products such as for example plasters. The comparative examples do not display permanent tack and exhibit short open times. The usually relatively high melt viscosities of the comparative formulations are disadvantageous for an application from the melt because a high application temperature would be required. This leads to an increased energy requirement and can result in undesired thermal degradation of the polyolefins.

[0081] Raw materials used:

[0082] Vestoplast® and Eastoflex® are amorphous poly-α-olefins from the manufacturers Evonik and Eastman, respectively:

[0083] Vestoplast 828: Flow point (ASTM D97)>150° C.

[0084] Vestoplast 703: Flow point (ASTM D97)>120° C.

[0085] Eastoflex 1060: Flow point (ASTM D97)>120° C.

[0086] Versify® is an ethylene copolymer from the manufacturer Dow:

[0087] Versify 4200: Flow point (ASTM D97)>150° C.

[0088] Versify 4301: Flow point (ASTM D97)>150° C.

[0089] Vistamaxx® is a propylene copolymer from the manufacturer ExxonMobil:

[0090] Vistamaxx 6502: Flow point (ASTM D97)>150° C.

[0091] Sukorez® SU 100 and Regalite® 1010 are hydrogenated hydrocarbon resins from the manufacturers Kolon Ind and Eastman, respectively.