REDUCING THE EDGE STICKINESS OF A ROLL OF ADHESIVE TAPE

Abstract

The invention relates to a method for reducing an end face stickiness a roll (21) of adhesive tape, by supplying a precursor (4) comprising organic polyfunctional silanes to a plasma stream, directing the plasma stream enriched with the precursor (4) at the roll end face (20), and coating the roll end face (20) with an SiOx coating.

Claims

1. A method for reducing the end face stickiness of a roll of adhesive tape, comprising: enriching a precursor with a plasma stream, directing the enriched plasma stream to a roll end face of an adhesive tape, and coating the roll end face with silicon dioxide, wherein the precursor comprises an organic polyfunctional silane.

2. The method as claimed in claim 1, wherein the organic polyfunctional silane is selected from the group consisting of hexamethyldisiloxane, (3-glycidyloxypropyl)trimethoxysilane, and octyltriethyoxysilane.

3. The method as claimed in claim 1, further comprising a mother roll slit transversely to a longitudinal direction to form individual rolls of adhesive tape, and wherein at least one of the individual rolls adhesive tape is unrolled and traverse wound.

4. The method as claimed in claim 1, wherein the silicon dioxide coating is applied to a thickness of 60 nm to 600 nm.

5. The method as claimed in claim 1, wherein the silicon dioxide coating is applied over the full area to the roll end face.

6. The method as claimed in claim 1, wherein the silicon dioxide coating has a constant thickness.

7. A roll of adhesive tape produced by the method of claim 1, comprising a roll end face and a silicon dioxide coating applied over the full area of the roll end face.

8. The roll of adhesive tape as claimed in claim 7, wherein the silicon dioxide coating has a thickness of 60 nm to 600 nm.

9. The roll of adhesive tape as claimed in claim 8, wherein the silicon dioxide coating has a constant thickness.

10. The roll of adhesive tape as claimed in claim 7, wherein the roll end face is contaminated.

Description

[0099] The invention is described by means of an exemplary embodiment in two figures, of which:

[0100] FIG. 1 shows a conceptual construction of a plasma nozzle that is used;

[0101] FIG. 2 shows an end face of a roll of adhesive tape, provided with an SiOx coating.

[0102] FIG. 1 shows the basic view of a plasma nozzle 1, the system in question being an OpenAir system from Plasmatreat GmbH.

[0103] The plasma nozzle 1 comprises a precursor unit 2, which in FIG. 1 is shown on the left, and a plasma unit 3. The precursor unit 2 generates a carrier gas 6 enriched with a precursor 4, while the plasma unit 3 generates a plasma 7. The precursor 4 and the plasma 7 are merged in a nozzle head 8.

[0104] The plasma 7 here is a high-energy process gas 11, more particularly an excited and ionized air-nitrogen mixture. For generation, the plasma unit 3 is first supplied through an inlet 9 with the process gas 11, the process gas 11 here being air or nitrogen or a mixture thereof. The process gas 11 is introduced through the inlet 9 into the plasma unit 3, and passes, through a plate 12 with drilled holes, into a discharge zone 13, through which the process gas 11 flows. In the discharge zone 13, the process gas 11 is conveyed past an electrode tip 14, to which a high-frequency alternating voltage of several kilovolts and a frequency of 10 kHz is connected. Between the electrode tip 14 and a counterelectrode, which may for example be a grounded stainless steel housing 16, a strong alternating electrical field is formed that leads to a corona discharge, which ionizes the process gas 11 flowing through the plasma unit 3 past the electrode tip 14, and converts it into a stream of the plasma 7. The plasma 7 is guided through the nozzle head 8, to which the precursor unit 2 is connected at a side inlet 17.

[0105] The side inlet 17 of the nozzle head 8 is connected to the precursor unit 2. The precursor unit 2 comprises a first feed for the precursor 4 and a second feed for the carrier gas 6. The carrier gas 6 used here may likewise be air or nitrogen or a mixture of air and nitrogen. The precursor 4 is atomized and supplied to the carrier gas 6 in droplet form; the mixture passes into a vaporizer 18, where the prevailing temperatures are above the boiling point of the precursor 4. The precursor 4 used may be an organic polyfunctional silane, examples being octyltriethoxysilane (OCS), (3-glycidyloxypropyl)trimethoxysilanes (GLYMO), and hexamethyldisiloxane (HMDSO).

[0106] The precursor 4 used here is a hexamethyldisiloxane (HMDSO), which is supplied to the carrier gas in an order of magnitude of 10, 20, 40 up to 150 grams per hour. The temperature in the vaporizer 18 is approximately 120 C., in other words above the boiling temperature of HMDSO, which is approximately 100 C.

[0107] A precursor gas 19 issuing from the vaporizer 18 is supplied to the nozzle head 8, where it is combined with the plasma 7. Accordingly, together with the plasma 7, the precursor 6 passes onto a roll end face 20.

[0108] FIG. 2 shows a roll 21 of adhesive tape with one of the two roll end faces 20. The roll 21 of adhesive tape consists of a rolled-up adhesive tape, which in turn comprises a substrate web 22, to one side of which a pressure-sensitive adhesive is applied over the full area, as a web 23 of pressure-sensitive adhesive. The substrate web 22 may be a film, a fabric or a paper.

[0109] The substrate web 22 and the pressure-sensitive adhesive web 23 together form the adhesive tape which is rolled up in FIG. 2. The substrate web 22 is customarily fabricated and provided in widths of 500 mm to 2000 mm and coated in this width as well with the pressure-sensitive adhesive. The substrate web 22 is wound up together with the web 23 of pressure-sensitive adhesive formed thereon, to give a wide roll of adhesive tape likewise in a width of 500 mm to 2000 mm. Only thereafter is the wide roll of adhesive tape slit to form rolls 21 of adhesive tape of the desired working width. After the slitting operation, the pressure-sensitive adhesive is exposed on the slit edges of the adhesive tape rolls 21, particularly the pressure-sensitive adhesive webs 23, and its adhesive properties may hinder further processing and product usage or even make them impossible.

[0110] The roll end face 20 of FIG. 2 is distinguished by an alternating sequence of substrate webs 22 and pressure-sensitive adhesive webs 23. In embodiments of the adhesive tape roll 21, the adhesive tape has a very small ratio of a thickness of the substrate web 22 to a thickness of the pressure-sensitive adhesive web 23. With adhesive tapes of this kind, which are referred to as thick-layer products, it is common to use viscoelastic materials for the substrate webs 22 with their own adhesive properties, and so virtually the entire end face 20 of the adhesive tape roll 21 is adhesive. As a result of the pressure-sensitive adhesiveness of the roll end face 20, after contact with other objects, the adhesive tape roll 21 on removal is destroyed or deformed or can no longer be deployed for use. This is a problem in particular with narrow rolls, which have only low mechanical strength.

[0111] The pressure-sensitive adhesiveness of the roll end face 20 is reduced by application of a passivation coat. The passivation coat in accordance with the invention is an SiOx coating, which is applied over the full area to the roll end face 20 in a plasma process, by means of the plasma nozzle 1 shown in FIG. 1.

[0112] The plasma nozzle 1 lies at a perpendicular angle to a surface of the roll end face 20, and ends in the nozzle head 8; the roll end face 20 is lying on a rotating table, which is not shown.

[0113] The treatment of the roll end face 20 takes place at or close to atmospheric pressure, although the pressure in the electrical discharge zone 13 of the plasma nozzle 1 may also be higher. Plasma 7 in this exemplary embodiment is an atmospheric-pressure plasma, which is an electrically activated, homogeneous reactive gas which is not at thermal equilibrium, having a pressure close to the ambient pressure in its zone of effect. Generally speaking, the pressure is 0.5 bar more than the ambient pressure. The electrical discharges or the ionization processes in the electrical field of the discharge zone 13 bring about activation of the process gas 11, and highly excited states are generated in the gas constituents. The precursor 4, in gas form or as an aerosol, is then supplied to the process gas 11 in the nozzle head 8, via a gas-conducting channel and via the side inlet 17, and it is this precursor 4 that forms the actual coat of silicon oxide on the surface of the roll end face 20.

Example 1

[0114] In this example, hexamethyldisiloxane (HMDSO) is supplied as precursor 4 to the process gas 11, and is excited in the process gas 11, with a significant increase in its reactivity. As a result, SiOx is accommodated optimally on the surface of the roll end face 20, and attaches firmly. In the present examples, the roll end faces 20 in question are those of ACX.sup.plus rolls, whose side edge stickiness is to be reduced. To start with, rather than the roll end face 20 itself, a swatch specimen is treated by means of the plasma process described above. The experimental system encompasses the following technical data, conditions, and parameters to be considered: [0115] Material for treatment: ACX.sup.plus-7056 as swatch specimen [0116] Plasma nozzle: generator FG 5001, fixed nozzle 216028WE [0117] Precursor: hexamethyldisiloxane (HMDSO) [0118] Precursor quantity: 10, 20, 40 g/hour [0119] Treatment number: 1- to 3-fold [0120] Treatment speed: 40 m/min for planar adhesive surfaces [0121] Nozzle distance: 15 mm [0122] PCT (pulse cycle time): 20% and 100% [0123] The glassy character of the silane layer is controlled via the PCT. PCT (pulse cycle time) refers to the fact that the plasma discharge is modulated by pulses. Switching on and off may improve the service lives of the electrode tips 14 and influence the formation of the reactive species. 100 percent corresponds to continuous discharge.

[0124] Table 1 shows the tack results of treated and untreated ACX.sup.plus-7056 swatch specimens in a standard Proptec method.

[0125] The Proptec method is a technique for measuring the instantaneous bond strength, hence the tack, of an adhesive. This may be employed as a quality feature for the passivation, and is able to indicate a quantified value.

TABLE-US-00001 HMDSO v Distance PCT Fmax Integral [g/l] [m/min] [mm] [%] [N] [Nmm] Remarks 20 40 15 20 0.588 0.131 Adhesive does not stick to die 20 40 20 100 1.095 0.693 Adhesive sticks a little to die 3 20 40 15 100 0.326 0.042 Adhesive does not stick to die 2 20 40 15 100 0.407 0.068 Adhesive does not stick to die 40 20 15 100 0.337 0.050 Adhesive does not stick to die 40 40 15 100 0.396 0.061 Adhesive does not stick to die 20 40 15 100 0.594 0.143 Adhesive does not stick to die 10 40 15 100 1.342 1.738 Adhesive sticks slightly to die Reference 5.631 7.945 Adhesive sticks strongly to die
Tesa ACX.sup.plus 7056 is a transparent, carrierless, acrylate adhesive tape with a foamed, acrylate-based pressure-sensitive adhesive with a thickness of 1500 m. One adhesive side of a swatch coated with ACX.sup.plus is coated with HMDSO, with the left-hand column showing the amount of HMDSO applied per hour, the second column showing the speed at which the nozzle head 8 is guided over the swatches, the third column showing the distance of the nozzle head 8 from the swatch, and PCT the pulse cycle time as stated above. Fmax indicates the maximum force needed in order to remove the die pressed onto the swatch, and the right-hand column reports the energy required for this.

[0126] The area of the circular Proptec die is 25.4 mm, and the die is pressed onto the swatch with a force of 4.5 N for 1 second.

[0127] The heading Remarks sets out how strongly the swatch (adhesive) adheres to the die. The bottom line shows the reference swatch, this being a swatch coated with ACX.sup.plus but without a plasma-polymerized coating. It is clearly apparent that relative to the untreated pressure-sensitive adhesive surface of the ACX.sup.plus product, there are marked reductions in the measurable force of adhesion. The force of adhesion is also referred to as tackiness. The abovementioned measurements, however, can also be transposed to the end face 20 of ACX.sup.plus rolls. In the case of the treated ACX.sup.plus rolls, it is found that not only do they not adhere to a metallic substrate but also that they can be taken up again without problems. A further factor is the dirt-repelling function of the plasma polymerization layer, since dust, fibers, and paper hardly remain adhering to the pressure-sensitive adhesive. For a period of eight hours as well it was not possible to discern any visible fouling of the nozzle components of the plasma unit 3 by the precursor 4.

LIST OF REFERENCE SYMBOLS

[0128] 1 plasma nozzle [0129] 2 precursor unit [0130] 3 plasma unit [0131] 4 precursor [0132] 6 carrier gas [0133] 7 plasma [0134] 8 nozzle head [0135] 9 inlet [0136] 11 process gas [0137] 12 plate [0138] 13 discharge zone [0139] 14 electrode tip [0140] 16 grounded stainless steel housing [0141] 17 side inlet [0142] 18 vaporizer [0143] 19 precursor gas [0144] 20 roll end face [0145] 21 adhesive tape roll [0146] 22 substrate web [0147] 23 pressure-sensitive adhesive web