PRESSURE-SENSITIVE ADHESIVE FOR PAPER BONDS

Abstract

A repulpable pressure-sensitive adhesive useful on polar and apolar papers and storage-stable comprises a polymer whose parent monomer composition comprises: a) 10 to 30 wt % of at least one compound of the formula (I)

CH.sub.2═CH—C(O)NR.sup.1R.sup.2  (I), wherein R.sup.1 is an unsubstituted alkyl group, a hydroxyalkyl group or an acetonyl radical and R.sup.2 is a hydrogen atom, an unsubstituted alkyl group, a hydroxyalkyl group, an acetonyl radical or an aminoalkyl group; b) 60 to 80 wt % of at least one compound of the formula (II)

CH.sub.2═CH—C(O)O—(CH.sub.2).sub.2—O—R.sup.3  (II), wherein R.sup.3 is an unsubstituted alkyl group, an alkoxyalkyl group or a (polyalkoxy)alkyl group; and c) 0.5 to 10 wt % of at least one monomer selected from the group consisting of acrylic acid, methacrylic acid and (C.sub.2-C.sub.4 hydroxyalkyl) acrylates.

Also disclosed is an adhesive tape comprising the pressure-sensitive adhesive, and use of the pressure-sensitive adhesive and/or the adhesive tape for producing water-soluble bonds.

Claims

1. Pressure-sensitive adhesive comprising at least one polymer whose parent monomer composition comprises: a) 10 to 30 wt % of at least one compound of the formula (I)
CH.sub.2═CH—C(O)NR.sup.1R.sup.2  (I), in which R.sup.1 is an unsubstituted alkyl group, a hydroxyalkyl group or an acetonyl radical and R.sup.2 is a hydrogen atom, an unsubstituted alkyl group, a hydroxyalkyl group, an acetonyl radical or an aminoalkyl group; b) 60 to 80 wt % of at least one compound of the formula (II)
CH.sub.2═CH—C(O)O—(CH.sub.2).sub.2—O—R.sup.3  (II), in which R.sup.3 is an unsubstituted alkyl group, an alkoxyalkyl group or a (polyalkoxy)alkyl group; and c) 0.5 to 10 wt % of at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, and (C.sub.2-C.sub.4 hydroxyalkyl) acrylates.

2. Pressure-sensitive adhesive according to claim 1, wherein R.sup.1 and R.sup.2 independently of one another are an unsubstituted alkyl group.

3. Pressure-sensitive adhesive according to claim 1, wherein R.sup.3 is an ethyl group or an ethoxyethyl group.

4. Pressure-sensitive adhesive according to claim 1, wherein the monomer composition comprises as monomer c) at least acrylic acid or 2-hydroxyethyl acrylate.

5. Pressure-sensitive adhesive according to claim 1, wherein the polymer is thermally crosslinked.

6. Adhesive tape comprising a pressure-sensitive adhesive according to claim 1.

7. A method of bonding a substrate with a water-soluble bond, said method comprising bonding the substrate with a pressure-sensitive adhesive according to claim 1.

Description

EXAMPLES

Measurement Methods

Gel Permeation Chromatography (GPC, Measurement Method A):

[0082] The figures for number-average and weight-average molecular weights M.sub.n and M.sub.w in this text are based on the determination by gel permeation chromatography.

[0083] The determination is made on a 100 μL sample which has undergone clarifying filtration (sample concentration 0.5 g/L). The eluent used is tetrahydrofuran containing 0.1 vol % of trifluoroacetic acid. Measurement takes place at 25° C. The pre-column used is a column of type PSS-SDV, 10 μm, ID 8.0 mm.Math.50 mm. Separation takes place using columns of the type PSS-SDV, 5 μm, 10.sup.3 Å (SN9090201) and also 5 μm, 10.sup.2 Å (SN9090200) each of ID 8.0 mm×300 mm (columns from Polymer Standards Service; detection by PSS-SECurity 1260 RID differential refractometer). The flow rate is 0.5 mL per minute. Calibration is made against PMMA standards (polymethyl methacrylate calibration).

Determination of Repulpability According to Tappi UM 213 (Measurement Method B):

[0084] The test paper used is “fluffed pulp” (Co. Machery-Nagel MN 270, 270 g/m.sup.2).

[0085] A three-layer assembly was produced, by bonding the test paper over its full area on both sides with the adhesive under investigation. The samples thus prepared were cut into pieces measuring 13×13 mm and were made up with test paper pieces of the same size in a beaker up to a weight of 15 g.

[0086] The samples together with 500 ml of mains water were placed in a mixer (Waring Blender Model 34BL47).

[0087] The blender contents were then mixed at around 15,000 rpm for 20 s. After that, the mixer was halted and residues of paper were washed back into the pulp from the edges of the mixer using mains water. This procedure was repeated twice, giving a total mixing time of 60 s. The resulting pulp was referred to as pulp 1.

[0088] The entire pulp 1 was placed in a disperser containing 2 l of mains water. Rinsing was carried out with mains water in order to transfer the pulp 1 without residue. The disperser was then made up with mains water to 5 l. Dispersing was carried out for 1 min, after which five beakers were each filled with 770 ml of the pulp 1 diluted accordingly; of these beakers, the first, third and fifth were used to produce test sheets.

[0089] For this purpose, the contents of a beaker were placed into a cylinder and made up with mains water to 7 l. Then air was blown through for 20 s and a waiting time of 20 s was observed in order to allow the foam to settle and the fibres to undergo self-orientation. The water was then withdrawn by suction through a sieve inserted in the base of the cylinder, after which vacuum was applied for 1 min.

[0090] The freshly formed sheet was covered with an outer card (substituted chromo card, 240 mm diameter, Estanit) (smooth side downwards) and rolled down with a 2 kg steel roller. The resulting assembly was removed, and the free side was covered with an outer paper (paper B13-c, 205 mm diameter, Estanit). This assembly was dried under reduced pressure at 100° C. in a drier for around 5 min.

[0091] After drying had taken place, the outer cards were carefully detached and the test sheet was examined for fibre extraction. Fibre extraction indicates residual stickiness, which is brought about as a result of inadequate repulpability on the part of the adhesive.

[0092] Ideally the outer cards can be removed without disruption, and the test sheet has two completely smooth sides. Slight fibre extraction was considered still to be adequate.

[0093] The test sheet was also examined both in transmitted light and in direct light for particles (specks). To pass the test, there must have been no particles apparent in the test sheet.

[0094] The test result recorded was “repulpable yes/no”.

Peel Adhesion (Measurement Method C):

[0095] The peel adhesion was determined at 23° C.+/−1° C. temperature and 50%+/−5% relative humidity.

[0096] The paper substrates used were stored continually beforehand under test conditions.

[0097] The paper substrates used were as follows: [0098] Raflatac 1600.9 label paper, bonded on a planer PE plate; [0099] CaCO.sub.3-containing paper: MediaPrint Silk 250 g, Stora Enso Uetersen, 100% CaCO.sub.3 in the coating; fastened on a PE plate using Tesa® 4965, [0100] wallpaper top paper 44540, 90 g/m.sup.2, Koehler SE; fastened on a PE plate using Tesa® 4965.

[0101] A strip of the adhesive under investigation, 20 mm wide and 250 mm long, was applied to the relevant paper. The pressure-sensitive adhesive strip was pressed on twice to the substrate with an applied pressure corresponding to a weight of 2 kg. The adhesive under investigation was subsequently peeled from the paper substrate [0102] immediately and [0103] in the case of the measurement on CaCO.sub.3-containing paper, additionally after storage of the bond for 3 d at 40° C./80% relative humidity and a subsequent 20 h under test conditions

[0104] at a velocity of 300 mm/min and at an angle of 180°. The force required to achieve this was recorded using a tensile testing machine. The measurement results are reported in N/cm and are averages from three measurements.

Splitting Force (Measurement Method D):

[0105] This test determines the split resistance of a paper in the z-direction. The split resistance or splitting force is the force needed in order to split the paper body in the z-direction.

[0106] The adhesive under investigation was applied to a splitting paper (paper splittable in the z-direction, 69 μm, 73 g/m.sup.2, splitting energy <30 cN/cm) on both sides by initial stroking with the finger in order to avoid air inclusions and subsequent rolling down twice with a manual roller. This bond was produced in a manner such that the ends of the strip of adhesive projected beyond the test element on one side and could be folded onto themselves and stuck together to form a finger tab. The measurements were made [0107] immediately and also [0108] after storage of the test specimen for 1 month at 40° C. and 80% relative humidity.

[0109] Strips 15 mm wide with a length of 20 cm were cut from the assembly using a steel rule. The finger tabs were pulled apart by hand until splitting of the paper became apparent.

[0110] The test specimen was clamped into a tensile testing machine using the finger tabs, freely hanging, at the top and bottom, and the strip was pulled apart with a velocity of 300 mm/min (measured in conditions 23° C., 50% relative humidity).

[0111] The force required to achieve this was recorded and is reported in Table 2 as the mean value from five measurements.

Rolling Ball Tack Test (Measurement Method E):

[0112] In this test, a steel ball with a weight of 5.6 g rolled from a ramp at a height of 65 mm onto a horizontal strip of the adhesive under test. The distance travelled by the ball before it came to rest was measured (test conditions 23° C., 50% relative humidity).

[0113] Prior to the measurement, the balls were cleaned with wadding and acetone and acclimatized under test conditions for 30 minutes, uncovered.

[0114] Prior to the measurement the adhesive was acclimatized under test conditions for 1 day.

Production of the Adhesives:

[0115] A 300 L reactor conventional for radical polymerizations was charged with a total of 100 kg of the monomers specified in Table 1, in accordance with the composition likewise specified there, and also with 72.4 kg of ethanol/water (70:30). After nitrogen gas had been passed through the reactor with stirring for 45 minutes, the reactor was heated up to 58° C. and 50 g of Vazo® 67 were added. The jacket temperature was then raised to 80° C. and the reaction was carried out constantly at a jacket temperature of 70° C. After a reaction time of 1 h a further 50 g of Vazo® 67 were added. To reduce the residual initiators, a further 50 g of Vazo® 67 were added after 6 h. After a reaction time of 24 h, the reaction was discontinued and the batch was cooled to room temperature. The solution was adjusted to a solids content of 30 wt %. The crosslinker specified in each case was then incorporated with stirring.

[0116] The resulting composition was coated in solution onto a siliconized PET film using a comma bar. The solvent was removed in a drying tunnel (20 min, 80° C.). The composition thus obtained was laminated, as the adhesive under investigation, onto a backing which is reported in each case for the test methods; the coat weight was 50 g/cm.sup.2.

TABLE-US-00001 TABLE 1 Composition of the adhesives Crosslinkers (wt %, based on polymer) Monomers (wt %, based on Titanium the monomer composition) diisopro- 2- N,N- Ethyl Alu- poxide Hy- Di- di- n- minium bis droxy- methyl- glycol Butyl acetyl- (acetyl- Acrylic ethyl acryl- acryl- acryl- ace- ace- No. acid acrylate amide ate ate tonate tonate)  1* 5 95 0.33  2* 10 90 0.33  3* 22 28 35 15 0.33 4 5 20 75 0.33 5 5 30 65 0.33 6 10 10 80 0.33  7* 10 90 2  8* 20 80 2 9 1 30 69 2 10  3 20 77 2 11  5 30 65 3 12  10 10 80 3 *Comparative example

TABLE-US-00002 TABLE 2 Test results Splitting force Peel adhesion (N/cm) After CaCO.sub.3 storage (1 paper month at (im- Wall- 40° C./ Re- mediate/ paper Rolling 80% pulp- Label after top ball Im- relative No. ability paper storage) paper (mm) mediate humidity) 1* No 2* No 3* Yes 7.7 6.42/ 6.2 208 not not 3.73 deter- deter- mined mined 4  Yes 7.8 7.0/7.0 8.2 56 29 27.2 5  Yes 8 6.5/6.0 7.95 78 29.2 27.5 6  Yes 8.4 6.5 83 29.2 28.1 7* No 8* No 9  Yes 7.2 7.7 41 26.9 44.1 10  Yes 7 7.2 9 30.2 37.6 11  Yes 7.3 8.5/7.9 8.8 80 29.3 33.8 12  Yes 6.3 6.9 34 29.3 33.6 *Comparative example