Acrylic pressure-sensitive adhesive and also adhesive tape furnished with acrylic pressure-sensitive adhesive

Abstract

An acrylic pressure-sensitive adhesive was to be provided that finds use especially in a reversible adhesive tape that is redetachable without leaving any residue, the adhesive tape having a particularly flat paper backing with high air permeability, and thus gives rise to particularly precise and flat paint edges when applied. This is achieved by an acrylic pressure-sensitive adhesive based on polymers having the following monomer composition: (a) 97% to 99% by weight of monomers from the group comprising 2-ethylhexyl acrylate or 2-octyl acrylate or n-heptyl acrylate or mixtures of at least two of said monomers, (b) 1% to 3% by weight of (meth)acrylic acid
and further comprising a crosslinking system, wherein the ratio of the reactive crosslinking groups and the carboxy groups of (meth)acrylic acid (b) is less than or equal to 7% and wherein the polymers are produced by emulsion polymerization.

The invention also provides an adhesive tape comprising a backing andapplied to at least one side of the backingan acrylic pressure-sensitive adhesive of the invention in the form of a dried polymer dispersion and also the use of such an adhesive tape.

Claims

1. An acrylic pressure-sensitive adhesive based on polymers having the following monomer composition: (a) 97% to 99% by weight of monomers from the group comprising 2-ethylhexyl acrylate or 2-octyl acrylate or n-heptyl acrylate or mixtures of at least two of said monomers, (b) 1% to 3% by weight of (meth)acrylic acid and further comprising a crosslinking system, wherein the ratio of the reactive crosslinking groups and the carboxy groups of (meth)acrylic acid (b) is less than or equal to 7% and wherein the polymers are produced by emulsion polymerization.

2. The acrylic pressure-sensitive adhesive according to claim 1, wherein the 2-octyl acrylate attains a maximum proportion in the monomer mixture of 85% by weight.

3. The acrylic pressure-sensitive adhesive according to claim 1, wherein the methacrylic acid is used in polymer formation, preferably in a proportion of 20.5% by weight.

4. The acrylic pressure-sensitive adhesive according to claim 1, wherein the crosslinking system is selected from the group comprising multifunctional aziridines, epoxides, carbodiimides or oxazolines or mixtures thereof.

5. An adhesive tape comprising a backing, having applied to at least one side of the backing an acrylic pressure-sensitive adhesive according to claim 1 in the form of a dried polymer dispersion.

6. The adhesive tape according to claim 5, wherein the coat weight of the acrylic pressure-sensitive adhesive on the backing, is between 20 and 200 g/m.sup.2, preferably between 25 and 75 g/m.sup.2, more preferably between 30 and 50 g/m.sup.2.

7. The adhesive tape according to claim 15, wherein the basis weight of the paper (taking into account any impregnation or lacquering with a release coating) is 25 to 250 g/m.sup.2, preferably 40 to 200 g/m.sup.2, most preferably 50 to 90 g/m.sup.2 and/or the thickness is between 50 and 200 m, preferably between 50 and 90 m.

8. The adhesive tape according to claim 5, wherein: (a) the input of impregnation agent is between 5 and 25 g/m.sup.2, preferably 9 and 20 g/m.sup.2, (b) the thickness is between 50 m and 90 m, preferably between 60 m and 80 m, (c) the elongation at break is between 3 and 13%, preferably between 5 and 11%, (d) the air permeability is less than 20 l/m.sup.2s, preferably less than 5 l/m.sup.2s.

9. The adhesive tape of claim 5, wherein the adhesive tape has the following properties: an adhesive strength on PVC or aluminium of 1.7 to 2.2 N/cm and/or a rolling ball tack of less than 50 mm.

10. A masking tape, based on the adhesive tape of claim 5.

11. A method of temporarily masking of a surface during a painting process, the method comprising: removably affixing the masking tape of claim 10.

12. The acrylic pressure-sensitive adhesive according to claim 4, wherein the the crosslinking system is selected from the group comprising aziridines, epoxides or carbodiimides or mixtures thereof.

13. The acrylic pressure-sensitive adhesive according to claim 12, wherein the crosslinking system is a polymeric aziridine having a molecular weight of greater than 1000 g/mol.

14. The adhesive tape according to claim 5, wherein the backing is a paper backing.

Description

[0112] The adhesive tape shall be elucidated in more detail hereinbelow with reference to a FIGURE, without wishing to give rise to a restriction of any kind.

[0113] FIG. 1 shows the adhesive tape in a lateral section.

[0114] In FIG. 1 the adhesive tape is shown in a section in cross direction (cross section), the tape consisting of a paper backing 1 to which a layer of an acrylic pressure-sensitive adhesive 2 has been applied on one side.

[0115] Before the invention is illustrated by means of examples, the measurement methods used will be described.

MEASUREMENT METHODS

Immediate Adhesive Strength

[0116] The adhesive strength (according to AFERA 5001) was determined as follows. The substrates used were a PVC plate (Kmadur H white 654 from Thyssen Krupp Plastics GmbH), an aluminium plate (alloy 5005A (AlMg1), anodized E6EV1 from Rocholl GmbH) and a commercially available 600 grit sandpaper. For the determination of the adhesive strength, the adhesive tape to be examined was cut to a width of 20 mm and a length of 25 cm, provided with a handling section and immediately thereafter in five replicate determinations pressed onto the relevant substrate with a 4 kg steel roller at an advance rate of 10 m/min. Immediately thereafter, the bondable sheet element was removed from the substrate at an angle of 180 using a tensile tester (from Zwick) at a pull-off rate of v=300 mm/min and the force necessary for this was measured under normal climatic conditions (231 C., 505% rel. humidity). The measured value (in N/cm) was the mean value of three individual measurements.

[0117] For an adhesive masking tape, adhesive strength values of 1.7 to 2.2 N/cm on both PVC and aluminium are considered optimal and thus in accordance with the invention.

[0118] Adhesive strength values outside these limits describe an unsuitable adhesive tape.

[0119] On sandpaper, the masking tape of the invention should have a value greater than 0.6 N/cm in order to be suitable. Values below 0.6 N/cm describe an unsuitable adhesive tape.

Adhesive Strength After Storage

[0120] In addition, the peeling behaviour of the examined adhesive tapes was investigated (adhesive strength after storage).

[0121] For the determination of the peeling behaviour, the adhesive tape to be examined was cut to a width of 20 mm and a length of 25 cm, provided with a handling section and immediately thereafter in five replicate determinations pressed onto the relevant substrate (PVC and anodized aluminium) with a 4 kg steel roller at an advance rate of 10 m/min. The plates were then stored in the climatic chamber for four days (96 hours) at 60 C. and 95% relative humidity. After the climate-controlled storage, the plates were reconditioned for at least 8 hours under normal climatic conditions (231 C., 505% rel. humidity) and the peel-off force after application then determined in analogous manner to the above-described adhesive strength test using a tensile tester and the arithmetic mean (in N/cm) of three individual measurements calculated.

Peeling Factor

[0122] To evaluate the peeling behaviour, the peeling factor is determined. This is calculated as the ratio of the adhesive strength after storage on the respective substrate (PVC or anodized aluminium) divided by the immediate adhesive force. For compositions of the invention this dimensionless factor is less than 1.65, which corresponds to a very low tendency to peeling.

Ghosting

[0123] For the visual evaluation of residues or ghosting, the adhesive tapes to be examined are stuck to the PVC plate and the aluminium plate in a width of 20 mm and a length of 25 cm. The adhesive tape is removed from the paint surface at an angle of 180 and at a rate of 300 mm/min. The paint surface is then visually assessed for residues at a shallow angle of 45 against a light source according to the following criteria: [0124] G1: Clean, no residues, no visible ghosting under normal indoor light and at an angle of 45 to the vertical direction [0125] G2: Clean, no residues, visible ghosting [0126] G3: Clean, residues, visible ghosting [0127] G4: Not clean, residues, visible ghosting

Rolling Ball Tack

[0128] The rolling ball tack was measured according to the PSTC-6 method (Test Methods for Pressure Sensitive Adhesive Tapes, 15th Edition; publisher: Pressure Sensitive Tape Council, Northbrook (Illinois), USA) with the following modifications: [0129] Use of stainless steel ball bearings (stainless steel 1.4401), diameter 7/16 in., mass 5.7 g. [0130] Preparation of the balls: Thorough cleaning with cellulose and acetone: the clean balls are stored in an acetone bath for 15 min before the measurement series (balls are completely immersed in acetone). At least 30 min before the start of the measurement, the balls are taken out of the acetone bath and conditioned by open storage under normal climatic conditions (231 C., 505% rel. humidity). [0131] Each ball is used for one measurement only.

[0132] The tackiness to the touch was determined as follows: As a measure of the tackiness to the touch at very short contact times, the so-called rolling ball tack was measured. An approximately 30 cm long strip of the adhesive tape was horizontally fastened under tension to the test surface with the adhesive side facing upwards. For the measurement, the steel ball was accelerated under the earth's gravitational field by rolling down a 65 mm high ramp (angle of inclination: 21). From the ramp, the steel ball was directed directly onto the adhesive surface of the sample. The distance travelled on the adhesive until the ball came to a standstill was measured. The roll path length thus determined serves as an inverse measure of the tackiness to the touch of the self-adhesive composition (i.e. the shorter the roll distance, the higher the tackiness to the touch and vice versa). The measured value (as a length in mm) was in each case the mean value of five individual measurements on in each case five different strips of the adhesive tape.

[0133] Values of less than 50 mm for an adhesive masking tape in the rolling ball test are considered optimal here and thus in accordance with the invention.

[0134] RBT values outside these limits describe an unsuitable adhesive tape.

Elongation at Break

[0135] The elongation at break is determined according to the AFERA 5004 test method.

Air Permeability

[0136] The air permeability is determined in accordance with EN ISO 9237. The measurement area is 20 cm.sup.2 and a test pressure of 2500 Pa is employed. The test samples are conditioned in accordance with DIN 53802 and ASTM D 1776. The Tester FX3300 air permeability tester from Textest Instruments was used for the actual test. In this test, the measured air permeability should be less than 20 l/m.sup.2s, preferably <5 l/m.sup.2s.

Molecular Weight

[0137] The molecular weight, as the number-average molecular weight M.sub.n and weight-average molecular weight M.sub.w, is determined by gel-permeation chromatography (GPC). THF (tetrahydrofuran) containing 0.1% by volume of trifluoroacetic acid is used as eluent. The measurement is carried out at 23 C. A PSS-SDV, 10, 10.sup.3 , ID 8.0 mm50 mm guard column is used. The columns used for the separation are PSS-SDV, 10, 10.sup.3 , 10.sup.5 and 10.sup.7 , each having ID 8.0 mm300 mm. The sample concentration is 0.5 g/l, the flow rate 0.5 ml per minute. The calibration is determined using the commercially available ReadyCal kit poly(styrene) high from PSS Polymer Standard Service GmbH, Mainz. This is converted into polymethyl methacrylate (PMMA) using the Mark-Houwink parameters K and alpha universal, so that the data are expressed in PMMA mass equivalents.

Viscosity Measurement

[0138] Viscosity is measured using an ARES rheometer (Rheometric Scientific) at room temperature and at a shear rate of 10 s.sup.1 with a cone-plate system having a diameter of 50 mm.

EXAMPLES

[0139] The adhesive tape of the invention is described hereinbelow in a preferred embodiment with reference to examples, without wishing therewith to subject the invention to any restriction. Also given are comparative examples representing unsuitable adhesive tapes.

[0140] To elucidate the inventive concept, polymer dispersions having the specified composition were tested.

[0141] The sample adhesive tapes are produced according to the following scheme:

[0142] Depending on the example, the polymer dispersions are optionally mixed with a crosslinker before coating. This is incorporated with the aid of a beaker agitator at moderate shear. For better coatability, the basic formulation thus prepared is then adjusted with a rheology additive (BorchiGel 0625, OMG Borchers) to a viscosity of 1000 mPa*s at a shear rate of 10 s.sup.1. The thickened samples are applied with a wire doctor blade to an impregnated washi paper (with a grammage of 50 g/m.sup.2) so as to obtain, after drying for 5 min at 105 C., a coating basis weight of approx. 30 g/m.sup.2.

TABLE-US-00001 TABLE 1 Monomer composition (values are in each case in wt %) Monomer P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 2-Ethylhexyl 98 40 30 98 99 97 85 40 97 91 93 acrylate 2-Octyl acrylate 98 58 84 38 40 N-Heptyl acrylate 98 14 30 N-Octyl acrylate 98 N-Butyl acrylate 98 2 Acrylonitrile 1 3 Acrylic acid 2 2 2 1 4 Methacrylic acid 2 2 2 2 2 2 1 3 2 Methyl methacrylate 7 8 8 Vinyl acetate 6 8 Styrene 2 Hydroxyethyl 2 acrylate

TABLE-US-00002 TABLE 1 Formulation Polymer Crosslinker Formulation Counterexample 1 P1 0 wt % crosslinker F1a Counterexample 2 P1 1 wt % aziridine F1b Counterexample 3 P1 0.25 wt % epoxy F1c Counterexample 4 P10 0.25 wt % aziridine F8a Counterexample 5 P11 0.25 wt % aziridine F9a Counterexample 6 P12 0.25 wt % aziridine F10a Counterexample 7 P13 0.25 wt % aziridine F11a Counterexample 8 P14 0.25 wt % aziridine F12a Counterexample 9 P15 0.25 wt % aziridine F13a Counterexample 10 P16 0.25 wt % aziridine F14a Example 1 P1 0.1 wt % aziridine F1d Example 2 P1 0.25 wt % aziridine F1e Example 3 P1 0.1 wt % epoxy F1f Example 4 P2 0.25 wt % aziridine F2a Example 5 P3 0.25 wt % aziridine F3a Example 6 P4 0.25 wt % aziridine F4a Example 7 P5 0.25 wt % aziridine F5a Example 8 P6 0.25 wt % aziridine F6a Example 9 P7 0.25 wt % aziridine F7a Example 10 P8 0.25 wt % aziridine F8a Example 11 P9 0.25 wt % aziridine F9a

[0143] The epoxy crosslinker used is Erisys GA-240 (N,N,N,N-tetrakis(2.3-epoxypropyl)-m-xylene-alpha,alpha-diamine from Emerald Performance Materials). The aziridine crosslinker used is NeoAdd PAX-521: multifunctional polymeric aziridine crosslinker from Covestro Deutschland AG.

TABLE-US-00003 Formulation F1a F1b F1c F1d F1e F1f Crosslinker PAX-521 PAX-521 PAX-521 (poly- GA-240 (poly- (poly- GA240 without aziridine) (epoxy) aziridine) aziridine) (epoxy) Crosslinker % SParameter 0 1 0.25 0.1 0.25 0.3 Adhesive specifications Immediate adhesive strength, 180, PVC 300 mm/min 1.7-2.2 2.51 2.03 1.51 2.18 2.15 2.20 ALU 300 mm/min 1.7-2.2 2.25 1.83 1.39 2.04 1.95 2.00 Sandpaper 600 grit 300 mm/min >0.6 1.19 0.52 0.39 0.82 0.80 1.10 Adhesive strength after storage 60 C./ 95% RH 96 h PVC 300 mm/min <4 3.61 3.19 2.43 3.55 3.45 3.23 Peeling factor <1.65 1.44 1.57 1.61 1.63 1.60 1.47 (adhesive strength after storage/ immediate adhesive strength) G1-G4 G1 G1 G1 G1 G1 G1 ALU 300 mm/min <4 3.43 2.63 2.11 3.25 3.04 2.91 Peeling factor <1.65 1.52 1.44 1.52 1.59 1.56 1.46 (adhesive strength after storage/ immediate adhesive strength) G1-G4 G1 G1 G1 G1 G1 G1 Rolling ball tack Average RBT <50 14.8 20 21.8 16.2 16.8 18.4 (mm) Formulation F2a F3a F4a F5a F6a F7a F8a F9a Crosslinker PAX-521 PAX-521 PAX-521 PAX-521 PAX-521 PAX-521 PAX-521 PAX-521 (poly- (poly- (poly- (poly- (poly- (poly- (poly- (poly- aziridine) aziridine) aziridine) aziridine) aziridine) aziridine) aziridine) aziridine) Crosslinker % SParameter 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 Adhesive specifications Immediate adhesive strength, 180 PVC 300 mm/min 1.7-2.2 2.07 2.10 2.08 2.18 2.12 2.16 2.02 2.18 ALU 300 mm/min 1.7-2.2 1.83 1.96 1.79 1.78 1.89 2.02 1.91 2.07 Sandpaper 600 grit 300 mm/min >0.6 0.95 1.45 0.99 0.86 0.84 0.91 0.82 0.85 Adhesive strength after storage 60 C./ 95% RH 96 h PVC 300 mm/min <4 2.99 3.46 3.05 3.02 3.21 3.18 3.29 3.50 Peeling factor <1.65 1.44 1.65 1.47 1.39 1.51 1.47 1.63 1.61 (adhesive strength after storage/ immediate adhesive strength) G1-G4 G1 G1 G1 G1 G1 G1 G1 G1 ALU 300 mm/min <4 2.51 2.69 2.79 2.47 2.84 3.09 3.00 3.27 Peeling factor <1.65 1.37 1.37 1.56 1.39 1.50 1.53 1.57 1.58 (adhesive strength after storagef immediate adhesive strength) G1-G4 G1 G1 G1 G1 G1 G1 G1 G1 Rolling ball tack Average RBT <50 21.2 22 19.3 24.7 21.1 18.6 17.4 19.5 (mm) Formulation F2a F3a F4a F5a F6a F7a F8a F9a Crosslinker PAX-521 PAX-521 PAX-521 PAX-521 PAX-521 PAX-521 PAX-521 PAX-521 (poly- (poly- (poly- (poly- (poly- (poly- (poly- (poly- aziridine) aziridine) aziridine) aziridine) aziridine) aziridine) aziridine) aziridine) Crosslinker % SParameter 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 Adhesive specifications Immediate adhesive strength, 180 PVC 300 mm/min 1.7-2.2 2.07 2.10 2.08 2.18 2.12 2.16 2.02 2.18 ALU 300 mm/min 1.7-2.2 1.83 1.96 1.79 1.78 1.89 2.02 1.93 2.07 Sandpaper 600 grit 300 mm/min >0.6 0.95 1.45 0.99 0.86 0.84 0.91 0.82 0.85 Adhesive strength after storage 60 C./ 95% RH 96 h PVC 300 mm/min <4 2.99 3.46 3.05 3.02 3.21 3.18 3.29 3.50 Peeling factor <1.65 1.44 1.65 1.47 1.39 1.51 1.47 1.63 1.61 (adhesive strength after storage/ immediate adhesive strength) G1-G4 G1 G1 G1 G1 G1 G1 G1 G1 ALU 300 mm/min <4 2.51 2.69 2.79 2.47 2.84 3.09 3.00 3.27 Peeling factor <1.65 1.37 1.37 1.56 1.39 1.50 1.53 1.57 1.58 (adhesive strength after storage/ immediate adhesive strength) G1-G4 G1 G1 G1 G1 G1 G1 G1 G1 Rolling ball tack Average RBT <50 21.2 22 19.3 24.7 21.1 18.6 17.4 19.5 (mm)

[0144] In the tables above, values that are outside the appropriate parameter ranges specified by the invention are shown in bold and underlined.

[0145] Examples 1 to 3 show that the monomers claimed according to the invention in combination with the amount of crosslinkers claimed according to the invention result in adhesive tapes having excellent suitability as adhesive masking tape.

[0146] Counterexample 1 is not crosslinked, the peel-off forces are much too high.

[0147] Counterexample 2 is too highly crosslinked, consequently an adequate adhesive strength is not achieved on sandpaper.

[0148] Counterexample 3 is crosslinked with an unsuitable crosslinker.

[0149] Examples 3 to 11 also reflect that the fact that suitable monomers with a suitable crosslinker in a suitable amount result in an adhesive that can be used in an adhesive masking tape that meets all requirements.

[0150] All counterexamples 4 to 10 fail in respect of the peel-off force from PVC.

[0151] In addition, almost all counterexamples show ghosting from G2 to G4.

[0152] The adhesive masking tape of the invention is intended in particular for use in the painting process for vehicles such as automobiles or for parts thereof such as bumpers, motorcycle tanks, etc. It is used to create sharp paint edges and is suitable for use on flat and highly curved surfaces and for sticking around very tight curves. The adhesive masking tape of the invention is distinguished by not leaving behind any residues and no ghosting on masked critical paint surfaces, even after high thermal stress.