Strapping adhesive tape

Abstract

The invention relates to an adhesive tape carrier made of a film, onto at least one side of which film an adhesive material is applied, wherein the film is a monoaxially stretched film made of polypropylene which contains at least 80 percent by weight polypropylene which has been processed in advance at least once, preferably has been extruded at least once, wherein the film has a stretching ratio during stretching in the longitudinal direction of 1:4 to 1:10.

Claims

1. A method of preparing an adhesive tape, said method comprising: (a) melting polypropylene including at least 80 wt % of polypropylene which has been processed at least once before, and optionally has been extruded, said melting resulting in polypropylene melt; (b) extruding the polypropylene melt to form a film; (c) monoaxially drawing the film with a draw ratio in the longitudinal direction of 1:4 to 1:10; and (d) coating the film with a pressure-sensitive adhesive; wherein the film after drawing exhibits at least one property that is not substantially changed compared to that exhibited by a comparison film prepared in the same manner except from 100 wt % virgin polypropylene, wherein the at least one property is selected from the group consisting of stress at 1% strain, stress at 10% strain, tensile strength, and elongation at break.

2. The method according to claim 1, wherein the polypropylene which has been processed at least once before has been extruded at least once before.

3. The method of claim 1, wherein a thickness of the film is between 20 and 2000 m.

4. The method of claim 1, wherein the draw ratio on drawing in the longitudinal direction is 1:5 to 1:9.

5. The method of claim 1, wherein the pressure-sensitive adhesive is selected from the group consisting of natural rubbers, blends of natural rubbers, synthetic rubbers, and mixtures thereof.

6. The method of claim 1, wherein the pressure-sensitive adhesive comprises tackifier resins.

7. The method of claim 1, wherein the pressure-sensitive adhesive comprises an additive selected from the group consisting of at least one UV protectant, other blending components, and mixtures thereof.

8. The method of claim 2, wherein a fraction in the film of polypropylene which has been extruded at least once is at least 85 wt %.

9. The method according to claim 1, wherein the polypropylene that is melted in (a) is composed 100% of polypropylene which has been processed at least once before, and optionally has been extruded.

10. The method according to claim 2, wherein the polypropylene that is melted in (a) is composed 100% of polypropylene which has been processed at least once before, and has been extruded at least once before.

11. The method according to claim 1, wherein the adhesive tape is an adhesive strapping tape.

12. The method according to claim 11, wherein the polypropylene is a polypropylene homopolymer or polypropylene/polyethylene copolymer having a melt index (MFI) between 0.5 to 2.

13. The method according to claim 12, wherein the polypropylene is a polypropylene block copolymer having MFI of 1.5 g/10 min, flexural modulus of 1280 MPa, and a crystallite melting point of 164 C.; wherein steps (b) and (c) are carried out on a single-screw extrusion unit with a flat die with flexible die lip in one layer, followed by a chill roll station, and a single-stage short-gap drawing unit; wherein said die operates at a temperature of 230 C.; and wherein said drawing unit draws the film in a draw ratio of 1:6.5.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows a typical construction of the adhesive tape of the invention.

(2) The product consists of a film (a) and an adhesive (b). Additionally there may also be a primer (c) used, for improving the adhesion between adhesive and carrier, and a reverse-face release (d) may be used as well.

(3) The carrier (a) consists of a monoaxially oriented polypropylene film having a preferred thickness of between 30 and 170 m.

(4) The adhesive (b) is a mixture of natural rubber or other elastomers and also various resins, and may optionally also include plasticizers, fillers, and aging inhibitors.

(5) It has surprisingly emerged that MOPP can be produced even with 100% recycled PP raw material, without significant change in the mechanical properties.

(6) This is surprising because the expectation would have been that the mechanical stress would degrade the PP raw material, with consequent impairment in the quality of the extrudate and hence in the mechanical properties of the film. As in the examples shown below, the values for both films are situated at the same level.

(7) The adhesive tape of the invention exhibits ready redetachability from a wide variety of substrates. On the other hand, however, redetachability exists even at plus temperatures, meaning that no residues are observed as a result of cohesive failure of the adhesive, no instances of adhesive transfer (poor adhesive anchoring), and no carrier splits are observed.

(8) The carrier has a sufficient internal strength in all three directions in space, and has a high impact strength.

(9) On the basis of the properties outlined, the adhesive tape can be employed outstandingly as an adhesive strapping tape for bundling and palletizing cardboard-boxed products and other goods, even at low temperatures.

(10) Furthermore, the adhesive tape can be used for outstanding fastening of moving parts such as doors, flaps, and the like on printers or refrigerators during transport from the manufacturer to the seller, and on to the purchaser, even at low temperatures.

(11) The adhesive tapes are redetachable without residue.

(12) The invention is illustrated below by a number of examples, without thereby wishing to impose any restriction on the invention.

EXAMPLES

(13) Raw Materials

(14) Dow 7C06: polypropylene block copolymer:

(15) MFI 1.5 g/10 min, non-nucleated, flexural modulus 1280 MPa, crystallite melting point 164 C. (Dow Chemical)

Inventive Example 1

(16) The film is produced on a single-screw extrusion unit with flat die with flexible die lip in one layer, followed by a chill roll station and a single-stage short-gap drawing unit. Recycled film material (the film had originally been produced from Dow 7C06) is extruded, the die temperature being 230 C. Chill roll temperatures and drawing roll temperatures are set so as to maximize the crystallinity of the film before and after the drawing operation. The draw ratio is 1:6.5.

(17) Film Properties (in Longitudinal Direction where Appropriate):

(18) TABLE-US-00001 Carrier thickness after drawing/m 87 Stress at 1% strain/MPa 24.7 Stress at 10% strain/MPa 141 Tensile strength/MPa 282 Elongation at break/% 37

Comparative Example 1

(19) The film is produced on a single-screw extrusion unit with flat die with flexible die lip in one layer, followed by a chill roll station and a single-stage short-gap drawing unit.

(20) Dow 7C06 is extruded, the die temperature being 230 C. Chill roll temperatures and drawing roll temperatures are set so as to maximize the crystallinity of the film before and after the drawing operation. The draw ratio is 1:6.

(21) Film Properties (in Longitudinal Direction where Appropriate):

(22) TABLE-US-00002 Carrier thickness after drawing/m 84 Stress at 1% strain/MPa 25.1 Stress at 10% strain/MPa 143 Tensile strength/MPa 287 Elongation at break/% 35

Test Methods

(23) The measurements are carried out (unless otherwise indicated) under test conditions of 231 C. and 505% relative humidity.

Flexural Modulus

(24) The test takes place according to ASTM D 790 A (secant modulus at 2% strain).

Crystallite Melting Point

(25) The crystallite melting point is determined as usual according to ISO 3146 by DSC at a heating rate of 10 K/min.

Thickness

(26) The thickness is measured according to DIN 53370.

Melt Index

(27) The melt index is measured as Melt Flow Index (MFI) according to DIN 53735. For polyethylenes, melt indices are usually reported in g/10 min at 190 C. with a weight of 2.16 kg, and for polypropylenes correspondingly, but at a temperature of 230 C.

Tensile Elongation Behavior

(28) The tensile elongation behavior is tested unless otherwise indicated in machine direction (MD, running direction). The tensile strength is expressed in MP and the elongation at break in %; both values are measured according to DIN 53455-7-5. The test results, particularly the elongation at break, should be made statistically reliable by means of a sufficient number of measurements.

(29) The 1% or 10% strain is determined according to DIN 53455-7-5 in the longitudinal direction.