PROTECTIVE FILMS MADE OF POLYOLEFIN SUPPORT MATERIAL, PRIMER AND RADIATION-CROSSLINKABLE HOT MELT ADHESIVE

Abstract

Described herein is a protection film comprising a polyolefin carrier material, a precoating of the polyolefin carrier material with a primer selected from polyurethane dispersions and a pressure-sensitive adhesive layer of a radiation-crosslinked hotmelt adhesive. A process for producing such protection films is also described.

Claims

1. A protection film comprising: (a) a polyolefin carrier material whose surface to be coated has been pretreated, (b) a precoating of the polyolefin carrier material with at least one primer selected from aqueous polyurethane dispersions; and (c) a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer is formed by radiation crosslinking of a radiation-crosslinkable hotmelt adhesive and wherein the radiation-crosslinkable hotmelt adhesive comprises at least one poly(meth)acrylate formed from (i) at least 50% by weight of C1- to C18-alkyl (meth)acrylates and (ii) at least one ethylenically unsaturated monomer which comprises at least one polar group, wherein the polar group is selected from the group consisting of carboxylic acid groups, carboxylic anhydride groups, hydroxyl groups, amide groups, urethane groups, urea groups, piperidinyl groups, piperazinyl groups, morpholinyl groups, imidazoyl groups, ureido groups, pyrrolidone groups and combinations of two or more of the recited groups; and wherein the radiation-crosslinkable hotmelt adhesive comprises at least one photoinitiator and the photoinitiator is in the form of an additive not bonded to the poly(meth)acrylate and/or the photoinitiator is incorporated into the poly(meth)acrylate by polymerization.

2. The protection film according to claim 1, wherein before crosslinking the radiation-crosslinkable poly(meth)acrylate has a glass transition temperature of not more than 10 C.

3. The protection film according to claim 1, wherein the poly(meth)acrylate of the hotmelt adhesive has a K value of at least 30.

4. The protection film according to claim 1, wherein the carrier material is selected from the group consisting of polyethylene and polypropylene.

5. The protection film according to claim 1, wherein the polyurethane of the polyurethane dispersion is constructed from a) at least one diisocyanate, b) at least one diol, of which b1) 10 to 100 mol % based on the total amount of the diols (b) have a molecular weight of 500 to 5000 g/mol and b2) 0 to 90 mol % based on the total amount of diols (b) have a molecular weight of 60 to 500 g/mol, c) at least one monomer distinct from the monomers (a) and (b) having at least one isocyanate group or at least one isocyanate-reactive group which further bears at least one hydrophilic group or a potentially hydrophilic group and d) optionally at least one further compound distinct from the monomers (a) to (c) having at least two reactive groups selected from alcoholic hydroxyl groups, primary or secondary amino groups or isocyanate groups and e) optionally at least one monofunctional compound distinct from monomers (a) to (d) having a reactive group which is an alcoholic hydroxyl group, a primary or secondary amino group or an isocyanate group.

6. The protection film according to claim 5, wherein the diisocyanates a) are selected from diisocyanates of the formula X(NCO).sub.2, wherein X represents an acyclic aliphatic hydrocarbon radical having 4 to 15 carbon atoms, a cycloaliphatic hydrocarbon radical having 6 to 15 carbon atoms, an aromatic hydrocarbon radical having 6 to 15 carbon atoms or an araliphatic hydrocarbon radical having 7 to 15 carbon atoms; the diols b1) are selected from polyester diols, polycarbonate diols and polyether diols; and the compound c) is selected from dihydroxycarboxylic acids, diaminocarboxylic acids and diaminosulfonic acids.

7. The protection film according to claim 1, wherein a content of anionic or potentially anionic groups in the polyurethane is 30 to 1000 mmol/kg of polyurethane.

8. The protection film according to claim 1, wherein the polyurethane of the polyurethane dispersion is formed using at least one amorphous polymeric polyol.

9. The protection film according to claim 8, wherein the amorphous polyester diol is constructed from a mixture of at least one aliphatic dicarboxylic acid having 3 to 10 carbon atoms and at least one aromatic dicarboxylic acid in a ratio of 0.5:1 to 2:1 and at least one alkanediol having 2 to 10 carbon atoms.

10. The protection film according to claim 2, wherein the amorphous polyester is constructed from adipic acid/isophthalic acid in a ratio of 0.5:1 to 2:1 and at least one alkanediol having 4 to 8 carbon atoms.

11. The protection film according to claim 1, wherein the polyurethane of the polyurethane dispersion comprises 10% to 80% by weight of at least one amorphous polyester diol having a molecular weight of more than 500 and up to 4000 g/mol and the amorphous polyester diol is composed of a mixture of at least one aliphatic dicarboxylic acid having 3 to 10 carbon atoms and at least one aromatic dicarboxylic acid in a ratio of 0.5:1 to 2:1 and at least one alkanediol having 2 to 10 carbon atoms.

12. The protection film according to claim 1, wherein the polyurethane of the polyurethane dispersion is chain-extended with at least one polyamine.

13. The protection film according to claim 1, wherein the radiation-crosslinkable poly(meth)acrylate is crosslinkable by irradiation with UV light and the photoinitiator is copolymerized into the radiation-crosslinkable poly(meth)acrylate in the form of an ethylenically unsaturated, copolymerizable photoinitiator in an amount of not less than 0.5% by weight.

14. The protection film according to claim 1, wherein the radiation-crosslinkable poly(meth)acrylate is formed to an extent of at least 60% by weight from C4- to C10-alkyl (meth)acrylates.

15. The protection film according to claim 1 wherein the radiation-crosslinkable poly(meth)acrylate is formed to an extent of 0.1% to 30% by weight, from the at least one monomer which comprises at least one polar group.

16. The protection film according to claim 1, wherein the hotmelt adhesive comprises at least one radiation-crosslinkable poly(meth)acrylate, wherein the radiation-crosslinkable poly(meth)acrylate is formed from (a1) at least 60% by weight of at least one acrylate selected from the group consisting of n-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, propylheptylacrylate and mixtures thereof, (a2) 1% to 5% by weight of at least one monomer having polar groups, wherein the polar groups are selected from the group consisting of carboxylic acid groups, carboxamide groups, pyrrolidone groups, urethane groups and urea groups, (a3) 0.5% to 4% by weight of at least one ethylenically unsaturated copolymerizeable photoinitiator, and (a4) 0% to 25% by weight of at least one further monomer distinct from the monomers (a1) to (a3).

17. The protection film according to claim 1, wherein the application rate of the pressure-sensitive adhesive is at least 2 g/m.sup.2.

18. The protection film according to claim 1, wherein the detachment from a substrate takes place by adhesion failure of the radiation-crosslinked adhesive layer, wherein the adhesive layer detaches from the substrate and remains entirely on the polyolefin carrier material.

19. The protection film according to claim 1, wherein the force for removal of the protection film from brushed steel is not more than 5 N/25 mm at 23 C.

20. A process for producing protection films, comprising: (1) precoating a polyolefin carrier material whose surface to be coated has been pretreated, with at least one primer, wherein the primer is selected from polyurethane dispersions; and (2) applying a pressure-sensitive adhesive layer is applied to the primer layer, wherein the pressure-sensitive adhesive layer is formed by radiation crosslinking of a radiation-crosslinkable hotmelt adhesive and wherein the radiation-crosslinkable hotmelt adhesive comprises at least one poly(meth)acrylate formed from (i) at least 50% by weight of C1- to C18-alkyl (meth)acrylates and (ii) at least one ethylenically unsaturated monomer which comprises at least one polar group, wherein the polar group is selected from the group consisting of carboxylic acid groups, carboxylic anhydride groups, hydroxyl groups, amide groups, urethane groups, urea groups, piperidinyl groups, piperazinyl groups, morpholinyl groups, imidazoyl groups, ureido groups, pyrrolidone groups and combinations of two or more of the recited groups; and wherein the radiation-crosslinkable hotmelt adhesive comprises at least one photoinitiator and the photoinitiator is in the form of an additive not bonded to the poly(meth)acrylate and/or the photoinitiator is incorporated into the poly(meth)acrylate by polymerization.

Description

EXAMPLES

[0132] Input materials: [0133] nBA n-butyl acrylate [0134] 2-EHA 2-ethlyhexyl acrylate [0135] MMA methyl methacrylate [0136] MA methyl acrylate [0137] AA acrylic acid [0138] Fl photoinitiator monomer: polymerizable photoinitiator (35% solution in MEK) of the formula F-1. [0139] MEK methyl ethyl ketone [0140] t-BPPiv tert-butyl perpivalate (75% solution in mineral oil) [0141] t-BPOc tert-butyl peroctoate [0142] Emuldur 381 A aqueous dispersion of an elastomeric polyester polyurethane, not chain extended with polyamine [0143] Luphen 700 aqueous dispersion of an elastomeric polyester-polyurethane, chain extended with polyamine

Example V1 without Polar Monomers

[0144] In a polymerization apparatus consisting of a glass reactor, a reflux cooler, a stirrer and a nitrogen inlet 164.43 g of MEK are initially charged under a light nitrogen stream and heated to 80 C. As soon as a temperature of 70 C. was achieved 21.39 g of a monomer mixture consisting of 630.00 g of 2-EHA, 63.00 g of MMA and 20.00 g of Fl were added. Upon reaching 77 C. 1.47 g of a starter solution of 3.92 g of t-BPPiv and 32.90 g of MEK were added and the mixture was polymerized for 3 min at >79 C. Then the remaining 713.00 g of monomer mixture were added over 3 h and 36.82 g of starter solution were added over 3 h 15 min. The temperature was then increased to 90 C. over 15 min and a solution of 2.43 g of t-BPOc in 21.63 g of MEK was added over 30 min. The vacuum was then applied and the solvent was distilled off at not more than 135 C. and less than 50 mbar. The mixture was then degassed with slow stirring for 1 h at 135 C. and the maximum achievable vacuum. The melt was drained into a PP cup.

[0145] K value (1% in THF): 47.9

[0146] Zero-shear viscosity at 110 C.: 41.3 Pa s.

Example B1 with Polar Monomers

[0147] In a polymerization apparatus consisting of a glass reactor, a reflux cooler, a stirrer and a nitrogen inlet 211.41 g of MEK are initially charged under a light nitrogen stream and heated to 80 C. As soon as a temperature of 70 C. was achieved 27.50 g of a monomer mixture consisting of 810.00 g of 2-EHA, 58.50 g of MMA, 22.50 g of AA and 25.71 g of Fl were added. Upon reaching 77 C. 1.84 g of a starter solution of 3.60 g of t-BPPiv and 42.30 g of MEK were added and the mixture was polymerized for 3 min at >79 C. Then the remaining 916.71 g of monomer mixture were added over 3 h and 45.90 g of starter solution were added over 3 h 15 min. The temperature was then increased to 90 C. over 15 min and a solution of 3.12 g of t-BPOc in 27.81 g of MEK was added over 30 min. The vacuum was then applied and the solvent was distilled off at not more than 135 C. and less than 50 mbar. The mixture was then degassed with slow stirring for 1 h at 135 C. and the maximum achievable vacuum. The melt was drained into a PP cup.

[0148] K value (1% in THF): 47.3

[0149] Zero-shear viscosity at 110 C.: 58.9 Pa s.

Example B2 with Polar Monomers and Little Photoinitiator

[0150] In a polymerization apparatus consisting of a glass reactor, a reflux cooler, a stirrer and a nitrogen inlet 179.28 g of MEK are initially charged under a light nitrogen stream and heated to 80 C. As soon as a temperature of 70 C. was achieved 40.41 g of a monomer mixture consisting of 397.60 g of n-BA, 230.80 g of 2-EHA, 147.20 g of MA, 20.00 g of AA and 12.57 g of Fl were added. Upon reaching 77 C. 1.61 g of a starter solution of 3.41 g of t-BPPiv and 28.72 g of MEK were added and the mixture was polymerized for 3 min at >79 C. Then the remaining 808.17 g of monomer mixture were added over 2 h 45 min and 32.13 g of starter solution were added over 3 h. The temperature was then increased to 90 C. over 15 min and a solution of 1.55 g of t-BPOc in 19.20 g of MEK was added over 30 min. The vacuum was then applied and the solvent was distilled off at not more than 135 C. and less than 50 mbar. The mixture was then degassed with slow stirring for 1 h at 135 C. and the maximum achievable vacuum. The melt was drained into a PP cup.

[0151] K value (1% in THF): 50.5

[0152] Zero-shear viscosity at 130 C.: 70.0 Pa s.

Example B3 with Polar Monomers and Elevated Photoinitiator Content

[0153] In a polymerization apparatus consisting of a glass reactor, a reflux cooler, a stirrer and a nitrogen inlet 179.28 g of MEK are initially charged under a light nitrogen stream and heated to 80 C. As soon as a temperature of 70 C. was achieved 40.74 g of a monomer mixture consisting of 394.00 g of n-BA, 230.80 g of 2-EHA, 147.20 g of MA, 20.00 g of AA and 22.86 g of Fl were added. Upon reaching 77 C. 1.65 g of a starter solution of 4.27 g of t-BPPiv and 28.72 g of MEK were added and the mixture was polymerized for 3 min at >79 C. Then the remaining 814.86 g of monomer mixture were added over 2 h 45 min and 32.99 g of starter solution were added over 3 h. The temperature was then increased to 90 C. over 15 min and a solution of 2.03 g of t-BPPiv in 19.20 g of MEK was added over 30 min. The vacuum was then applied and the solvent was distilled off at not more than 135 C. and less than 50 mbar. The mixture was then degassed with slow stirring for 1 h at 135 C. and the maximum achievable vacuum. The melt was drained into a PP cup.

[0154] K value (1% in THF): 47.5

[0155] Zero-shear viscosity at 130 C.: 49.0 Pa s

Example B4 with Polar Monomers and Elevated Photoinitiator Content

[0156] In a polymerization apparatus consisting of a glass reactor, a reflux cooler, a starer and a nitrogen inlet 179.28 g of MEK are initially charged under a light nitrogen stream and heated to 80 C. As soon as a temperature of 70 C. was achieved 41.65 g of a monomer mixture consisting of 389.20 g of n-BA, 230.80 g of 2-EHA, 147.20 g of MA, 20.00 g of AA and 45.71 g of Fl were added. Upon reaching 77 C. 1.65 g of a starter solution of 4.27 g of t-BPPiv and 28.72 g of MEK were added and the mixture was polymerized for 3 min at >79 C. Then the remaining 832.91 g of monomer mixture were added over 2 h 45 min and 32.99 g of starter solution were added over 3 h. The temperature was then increased to 90 C. over 15 min and a solution of 2.03 g of t-BPPiv in 19.20 g of MEK was added over 30 min. The vacuum was then applied and the solvent was distilled off at not more than 135 C. and less than 50 mbar. The mixture was then degassed with slow stirring for 1 h at 135 C. and the maximum achievable vacuum. The melt was drained into a PP cup.

[0157] K value (1% in THF): 47.0

[0158] Zero-shear viscosity at 130 C.: 38.2 Pa s

[0159] Measurement of Zero-Shear Viscosity

[0160] The zero-shear viscosity is the threshold value of the viscosity function at infinitely low shear rates. It is measured with an Anton Paar MCR 100 rheometer (US 200 evaluation software) in plate/plate geometry. The samples are measured under oscillatory shear at a small shear amplitude of 10%. Temperature 130 C. (or as stated), angular frequency ramp log 100-0.1 1/s, measuring gap 0.5 mm, evaluation according to Carreau-Gahleitner I, piston diameter 25 mm.

[0161] Film Pretreatment:

[0162] F1 (comparative): corona-pretreated PE film

[0163] F2-F3: PE film precoated with adhesion promoter (primer);

[0164] in each case coated with 0.3 g/m.sup.2 (solid) of primer (cf. table 1)

[0165] F4 (comparative): plasma-pretreated film

[0166] In the corona treatment the film surface is treated by a dielectric discharge in the atmosphere of the ambient air. The discharge activates a multiplicity of chemical reactions between the ambient air and the film surface. This increases the surface energy of the film, which provides for better wettability for example.

[0167] By contrast with the corona treatment in the plasma treatment the discharging takes place in an atmosphere with an elevated nitrogen content. This allows the effectiveness of the surface treatment to be further improved by further increasing the surface energy of the film.

[0168] Film Precoating Procedure:

[0169] For precoating, a corona-pretreated 50 m polyethylene film is coated with an aqueous primer dispersion. The application rate after drying is 0.3 g/m.sup.2.

TABLE-US-00001 TABLE 1 Primer for film precoating Example Primer F2 Emuldur 381 A polyurethane dispersion F3 Luphen 700 polyurethane dispersion

[0170] Performance Tests:

[0171] All measurements are carried out at room temperature (20 C.) unless explicitly otherwise stated.

[0172] The pressure-sensitive adhesives were heated to 120 C. and from the melt doctor-coated onto siliconized PET film at an application rate of 10 g/m.sup.2 (for assessing the anchoring on the carrier film) or 15 g/m.sup.2 (for assessing ease of removal from brushed steel) and irradiated with UVC light. The film was then transferred to a commercially available pretreated 50 m PE film as described above (cf. table 1) as a carrier. The carrier coated with a pressure-sensitive adhesive was cut into 25 mm wide test strips.

[0173] a) Anchoring on PE Film

[0174] Polyethylene film strips (PE) coated with adhesive are examined with regard to the adhesion of the adhesive to the PE carrier. An attempt is made to rub the adhesive layer off the PE film at one point with a thumb (max. 10 repetitions). The quality of the anchoring is assessed using grades:

[0175] 0: easy to rub off;

[0176] 1: quite hard to rub off;

[0177] 2: hard to rub off;

[0178] 3: very hard to rub off;

[0179] 4: impossible to rub off.

[0180] The target results are ideally impossible to rub off or very hard to rub off.

[0181] b) Ease of Removal from Brushed Steel

[0182] In the determination of peel strength (adhesion) a 25 mm wide test strip is in each case bonded to a test specimen made of brushed steel (Ra=2.5 m) and rolled once with a 1 kg roller. One end is then clamped in the upper jaws of a tensile strain tester. The adhesive strip is removed from the test surface at a speed of 300 mm/min and an angle of 180, i.e. the adhesive strip is bent and removed parallel to the test specimen and the force required therefor is measured. The measure for peel strength is the force in N/25 mm obtained as the average value from at least two measurements. Peel strength is determined after 24 h and 7 d from bonding under defined storage conditions. The test method corresponds substantially to the Finat test method FTM 1.

[0183] Ease of removal is assessed by examination of the residues on the substrate surface (brushed steel):

[0184] A: adhesion failure, no residues;

[0185] R: adhesion failure, isolated residues;

[0186] K: cohesion failure, film splits between substrate and carrier;

[0187] A0: swapover, complete transfer of the adhesive film from the carrier to the substrate.

[0188] The target result is ideally residueless removal. In addition the force required for removal is measured in N/25 mm. The target result is the lowest possible removal force in the range of 0.5-5 N/25 mm at room temperature (23 C.).

[0189] The results are summarized in tables 2 to 3.

TABLE-US-00002 TABLE 2 Effects of film pretreatment on anchoring of the pressure-sensitive adhesive on PE film UV Anchoring after dose .sup.1) 24 h standard 7 d standard 24 h Ex. Film [mJ/cm.sup.2] climate .sup.2) climate .sup.2) under water V1 .sup.3) F1 .sup.3) 60 0 0 1-2 V1 .sup.3) F3.sup. 60 1 1 4 B2 F1 .sup.3) 60 0-1 1 3 B2 F2.sup. 60 1-2 not determined not determined B2 F3.sup. 60 3 3-4 4 B2 F4 .sup.3) 60 1 not determined not determined B4 F1 .sup.3) 60 1-2 1-2 3 B4 F2.sup. 60 2-3 not determined not determined B4 F3.sup. 60 4 4 4 B4 F4 .sup.3) 60 2 not determined not determined .sup.1) UV-C radiation dose .sup.2) 23 C., 50% rel. humidity .sup.3) comparative test

[0190] The results show that anchoring on the PE film can be optimized by pretreatment. Plasma pretreatment improves this only slightly compared to corona pretreatment (F1 vs. F4). The polyurethane-based primers (F2, F3) result in better anchoring than corona or plasma pretreatment alone (F1, F4). Luphen 700 (polyurethane) (F3) is particularly suitable.

[0191] The presence of polar groups in the hotmelt adhesive is advantageous for good anchoring on primed film: In the absence of such groups even inventive primers (V1/F3) achieve less satisfactory anchoring compared to inventive hotmelt adhesive comprising polar groups (B2/F3, B4/F3). A higher crosslinking density of the pressure-sensitive adhesive is also advantageous (B4 vs. B2).

TABLE-US-00003 TABLE 3 Effect of crosslinking density of the pressure-sensitive adhesive on ease of removal UV Ease of removal after dose .sup.1) 24 h standard 7 d standard 7 d at 50 C./ Ex. Film [mJ/cm.sup.2] climate .sup.2) climate .sup.2) 85% r.h. B4 F3 0 R13.5N/25 mm R10N/25 mm K-16N/25 mm B4 F3 20 A2N/25 mm A2N/25 mm A1N/25 mm B4 F3 60 A0.5N/25 mm A0.5N/2 mm A0.5N/25 mm B1 F3 0 K10N/25 mm K9N/25 mm K9N/25 mm B1 F3 20 A2N/25 mm A2N/25 mm AN/25 mm B1 F3 60 A1.7N/25 mm A1.6N/25 mm A1.3N/25 mm .sup.1) UV-C radiation dose .sup.2) 23C., 50% rel. humidity A: adhesion failure, no residues R: adhesion failure, isolated residues K: cohesion failure

[0192] The results show that with increasing crosslinking density (higher UV dose) residueless removal is possible when using the pretreated PE film. Even the uncrosslinked samples (UV dose 0) show no swapover which demonstrates the good anchorage resulting from use of the primed film (F3). Further increasing the UV dose (UV dose of 60) reduces the removal force without altering removal behavior.

[0193] Contact Angle Measurements:

[0194] To examine the differences between the primer Luphen 700 (polyurethane 1) (F3) on the one hand and the primer Emuldur 381 A (polyurethane 2) (F2) on the other hand, the contact angle of a water droplet on the primed films was determined.

[0195] To this end triplicate measurements were taken on three different sites of the pretreated film in each case. In each case three test strips of 15 cm were cut out of the film in defined regions (cf. FIG. 1) and wetted with a droplet of water, Measurement of contact angle was carried out with an instrument from Krss (Krss DAS 100).

[0196] FIG. 1 indicates the position of the three test strips #1, #2 and #3.

[0197] The average values of triplicate measurements on the three test strips are shown in each case:

TABLE-US-00004 TABLE 4 Contact angle of dist. water on PE film treated with different primers Contact angle (H.sub.2O) Film Strip #1 Strip #2 Strip #3 F2 102.3 +/ 1.1 83.3 +/ 4 76.9 +/ 1.8 F3 80.2 +/ 0.9 79.1 +/ 2.3 80.7 +/ 1.9

[0198] The standard deviations of the triple determinations are low, thus indicating that the measured results may be regarded as reproducible. It is striking that in example F2 there are significant deviations in the contact angle from one test strip to another while the primed film F3 has contact angles on all three test strips that differ from one another only slightly. Different contact angles occur in the case of different polarities of the surfaces and these may be brought about for instance by incomplete wetting or concentration of surface-active substances. They may be an indication of an inhomogeneous film surface which reduces anchoring efficiency. F3 is particularly preferred since this example has a highly homogeneous film surface which brings about good anchoring of the adhesive to the film.