GB2057916A

GB2057916A - Pressure sensitive adhesives and tapes

Info

Publication number: GB2057916A
Application number: GB7926148A
Authority: GB
Original assignee: Nichiban Co Ltd
Current assignee: Nichiban Co Ltd
Priority date: 1979-07-13
Filing date: 1979-07-26
Publication date: 1981-04-08
Also published as: NO794055L; DK299380A; CA1142038A; NL7908772A; DE2930554A1; BE884284A; NZ191167A; DE2954420C2; FR2460984A1; ES482906A1; IL60011A; CH644390A5; SE7909765L; JPS5626968A; DK153565C; IL60011A0; GB2058610B; IT1198312B; FI793667A; AU527706B2

Abstract

Pressure sensitive compositions and tapes are described based on elastomers and containing thickeners and optionally other polymers and additives. The tapes are particularly useful for packaging vegetables and flowers since preferably the adhesive coating will bond firmly to itself but will bond with a peelable bond to the goods packaged within it.

Description

SPECIFICATION Pressure sensitive adhesives and tapes It is known to tie bundles of vegetables or floweres or other goods using a band of pressure sensitive tape, which may be in contact with the flowers or vegetables or other goods. The tapes all comprise a flexible substrate carrying adhesive and broadly there are three systems. In one adhesive is applied to the substrate at one end on one surface and at the other end on the opposite surface. In use the ends are overlapped and the two adhesive surfaces pressed together to make a permanent bond. This suffers from the disadvantage that tapes of differing iengths have to be pre-cut and tape that is suitable for one size bundle cannot be used for a different size. In another the substrate carries a continuous coating of pressure sensitive on one surface and at regular spaced intervals on the other surface.When tying a bundle the tape is cut to length and the ends are overlapped and the overlying continuous adhesive and discontinuous adhesive form a permanent bond. In a third system a continuous layer of adhesive is applied to both sides of the tape and overlapping areas are pressed together when tying a bundle to form a permanent bond.

In all these tapes the vegetables or flowers or other goods are held together by the tightness of the tape and there is no bonding between the goods and the tape. As a result the goods may fall out of the bundle since if the goods are tied sufficienty strongly to prevent this it is liable to damage the goods being packaged.

Pressure sensitive tape according to the invention comprises a substrate carrying a pressure sensitive adhesive and preferably the tape comprises a substrate carrying a continuous coating on one side of a pressure sensitive adhesive that will bond firmly to itself substantially without creep but will bond with a peelable bond to the flowers or vegetables. Thus the tape can be wrapped around the goods to be packed and overlying layers of the adhesive composition pressed together to form a firm and permanent bond but whereas previously the tape was designed not to be adhesive to other surfaces the tape of the invention preferably will bond slightly to the flowers or vegetables. The degree of bonding to the packaged goods must be such that the tape can easily be peeled off them without inflicting damage.This reduces the risk of the packaged goods sliding out of the package during transport or handling.

Conveniently the adhesive is present on the tape as substantially continuous coating on one side only. Bundles can then be packaged with this tape to any size and packaging pressure using simple tying machinery regardless of the size of bundle to be tied.

The strength of bond should preferably also be such that where the adhesive coating bonds firmly to itself the bond is substantially creep resistant. This means that if the goods swell, for instance as a result of immersion into water for cleansing, the bond does not slip due to the swelling. Instead the tape will remain as a thight wrapping around the goods at all times.

These are all preferred features of the tape which, broadly according to the invention, is a pressure sensitive tape comprising a waterproof substrate carrying a pressure sensitive adhesive coating composition that comprises 100 parts by weight of elastomer, 5 to 1 50 parts by weight of thickener, 0 to 40 parts by weight of another polymer and 0 to 1 50 parts by weight of additives. The ingredients of the formulation are preferably so formulated that the tape has the properties described above. The pressure sensitive adhesive composition itself forms a further part of the invention.

As mentioned above the adhesive is preferably present as a coating on one surface only of the tape and such an embodiment of the invention is illustrated in the accompanying drawings in which Figure 1 is a perspective view of the tape of the invention.

Figure 2 is a sectional view cut along line ll-ll of Fig. 1.

Figure 3 is an explanatory schematic view showing the condition of the tape of the invention as it is being used.

As shown in these drawings the tape 3 comprises a waterproof substrate 1 carrying an adhesive coating 2. It may be presented initially in the form of a continuous roll, as shown in Fig. 1 from which lengths are cut of the size necessary for packaging the desired bundle of vegetables or other goods 4, as shown in Fig. 3. The coating 2 is on the inner most surface of the tape and the ends 3a of the tape are pressed to one another. The coating bonds releasably to the vegetables 4 around the bundle and firmly to itself in the end regions 3a.

For convenience this invention is described primarily with reference to the packaging of flowers and vegetables, especially leaf and root vegetables, but the invention is also applicable to the packaging of a wide variety of other goods.

The substrate of the tape can be any flexible substrate that has good water resistance.

Preferably the substrate is printable. It may be pre-printed with information about production or packaging, and/or may be classified, for instance by colour or size, with respect to the kind of goods to be tied. Preferred substrates are films of polypropylene, polyethylene, unplasticised PVC, and polyester. The base film preferably has a thickness of from 20 to 60 microns but other thicknesses can be used.

The elastomer used in the adhesive composition is preferably selected from the group consisting of natural rubber, synthetic rubber such as butyl rubber (for example, Butyl No. 268, Esso Standard Petroleum Co.), polyisoprene rubber and block copolymer such as styreneisoprene-styrene block copolymer or styrene-butadiene-styrene block copolymer.

Mixtures may be used.

As the said other polymer, polyisobutylene (molecular weight of about 7,000 to 20,000) and polybutene (molecular weight of about 1 ,000 to 10,000) are preferred.

For thickener, polyterpene, rosin ester and petroleum resins are preferred. Among them, such are commercially available, for example, polyterpene having a softening point of 100"C or more, rosin ester and petroleum resin. For example polyterpene such as Guintone A 1 00, D 1 00, D 200, C 100, C200 S of Japan Geon Co., Ltd., alicyclic hydrocarbon such as Arcon P 100.P 11 5, P 1 25 of Arakawa Chemical Industry Co., Ltd., hydrogenated hydrocarbon resin such as Escorez 5300 and 5320 of Esso Chemical Co., Ltd., isoprene hydrocarbon resin such as Escorez 1304, 1310 and 1315 of Esso Chemical Co., unsaturated hydrocarbon resin such as Escorez 1 202 of Esso. Chemical Co. and hydrocarbon resin such as Tack-Ace A 100 of Mitsui Petroleum Chemical Co., Ltd. Mixtures may be used. The use of the thickener overside the range of 5 to 1 50 parts per 100 parts elastomer lowers the self-adhesiveness and creep resistance and adversely influences the capacity of a tape for tying.

An additive may be added to the composition to give an adequate control on cohesiveness and self-adhesiveness. For example, calcium carbonate, zinc oxide, titanium oxide, vegetable oil or modified vegetable oil (castor oil, colza oil, soybean oil and Factice etc), paraffinic or aromatic process oil (for example, Flexon 765, 110, 11 2 and 876 of Esso Chemical Co.), polybutene, liquid polyisobutylene, or polyterpene having a softening point of 20"C or higher may be used.

When using the additive in an amount over 1 50 parts by weight, cohesiveness and selfadhesiveness may be ill-balanced, and result in a bad initial adhesivity and make the instantaneous strong bond unsure. Any liquid additives are preferably used in an amount of 20 parts by weight or less in order to gain a balanced cohesiveness.

The adhesive composition thus prepared is coated on one surface of the base material, dried and wound up in order to prepare an adhesive tape.

The adhesive composition is ordinarily coated in a thickness of about 5 to 30 eel in dry state.

Before coating a primary treatment is preferably made on the basic film according to the conventional manner such as coating a primer layer.

The pressure sensitive adhesive forms a weak adhesive layer having a low polarity, but has a strong adhesiveness between the adhesive layers itself. Therefore the adhesive tape has its distinctive feature in its weak adhesiveness and strong self-adhesiveness which are very different from those of the conventional rubber- or acrylic-adhesives.

The preferred tape, coated on one suface only, can easily be cut to length and mechanically tied from a roll as shown in Fig. 1 and thus it is unnecessary to pre-cut the tape.

It is easily possible to formulate adhesive compositions for use in the invention and tapes coated with such compositions such that the tape has a suitable weak and peelable bond to the goods being packaged but a firm self-adhesive bond and that the bond has good creep resistance under constant load. This latter factor is of value in order to resist expansion of the volume of the package during water adsorption by it. It is also desirable to formulate the composition such that instantaneous self-adhesion occurs when pressing the adhesive coating to itself.

It is desirable that the adhesive layer has an adhesive strength of about 100 to 700 g per widtn of 20 mm (i.e. an adhesive strength obtained by contact-bonding the adhesive tape on a steel plate under the pressure of 2 kg/cm2), and a self-adhesive strength (auto-adhesive strength) over 900 g/20 mm width (i.e. an auto-adhesive strength obtaind after 10 minutes from bonding together the adhesive faces of the pressure sensitive adhesive tape). If the tape has a too high adhesive strength and the tape is used to tie up a soft vegetable such as spinach, the adhesive take adheres strongly to the leaf vegetables and they may be damaged when it is peeled from them.

To define the various bonding strengths more accurately we define below precise tests that may be used for measuring theses.

To measure initial adhesive strength a smooth edged surface of a metal rod having diameter of 5 mm is pressed into contact with the surface of the adhesive tape for one second under a load of 100 g at 20"C under a relative humidity of 65%. The initial adhesive strength is the peeling resistance measured when peeling this adhesive tape at a peeling velocity of 10 mm per second (see ASTM Special Technical Publication No. 360).

To measure the adhesive strength, adhesive tape with a width of 20 mm is press adhered by a roller having a weight of 2 kg onto a stainless steel panel and the idle surface is folded back onto the panel surface at an angle of 180 . The adhesive strength is the peeling resistance obtained by peeling off the tape at a peeling velocity of 300 mm per minute. The method is conducted according to JIS-Z 1 522.

To measure self-adhesion a 1 5 cm length of tape having a width of 20 mm is pressed upon itself in its central region over a length of 25 mm, with the adhesive faces in contact, with a roller having a weight of 1 kg. The self-adhesion is the peeling resistance which is obtained by peeling off the non-adhered end of the tape at an angle of 180 at a peeling velocity of 300 mm per minute. During this the faces are kept in alignment with one another.

To measure the self-adhesion keeping strength faces of the adhesive coated tape are bonded to one another as above, one free end of the tape is fixed and a load of 500 grams is attached to the other end of the tape for one hour at 20"C and a relative humidity of 65%. The extension after an hour is measured and is recorded as the self-adhesion keeping strength and is an indication of the creep resistance of the adhesive composition.

The composition is preferably such as to give values as shown in Table 1.

Table 1 Initial adhesive strength (9/5 mm diameter): 200-700 Adhesive strength (g/20 mm width): 100-700 Self adhering strength (9/20 mm width): > 900 Self adhesion keeping strength (mm/500 g.hr): 0-7 The corresponding properties are measured for some commercially available tapes, especially for packing tapes. The results are shown in Table 2.

Table 2 Kind of Tape and Formulation Initial Adhesive of Adhesive Composition Adhesive Strength (parts) Strength (9/20 mm (g/5 mm width) diameter (1) Polypropylene basic film A. Natural rubber 50 Clear 850 540 SIS 50 Coloured 800 450 Petroleum resin 85 B. Natural rubber 100 Clear 1,000 720 Petroleum resin 90 Coloured 850 630 C. Natural rubber 100 Clear 830 710 Polyterpene 1 30 Coloured 840 650 Filler 30 D. Natural rubber 100 Coloured 990 730 Polyterpene 90 Filler 90 (2) Cloth basic film Reclaimed rubber 100 Coloured 600 1,200 Resin rubber 50 Filler 50 (3) "Cellophane" basic film Natural rubber 100 Clear 700 Resin rubber 85 Coloured 570 630 Table 2 (Cont.) Self Kind of Tape and Formulation Self- Adhesion of Adhesive Composition Adhesive Keeping (parts) Strength Property (9/20 mm (mm/500 width) g.hr) (1) Polypropylene basic film A.Natural rubber 50 Clear 1 ,000 (22)* SIS 50 Coloured 950 (16) Petroleum resin 85 B. Natural rubber 100 Clear 1,000 (12).

Petroleum resin 90 Coloured 900 11 C. Natural rubber 100 Clear 1,250 (17) Polyterpene 1 30 Coloured 1,250 (7)* Filler 30 D. Natural rubber 100 Coloured 1,000 (12).

Polyterpene 90 Filler 90 (2) Cloth basic film Reclaimed rubber 100 Coloured 1,000 (130).

Resin rubber 50 Filler 50 (3) "Cellophane" basic film Natural rubber 100 Clear 600 (55) Resin rubber 85 Coloured 900 (19)' Note: : 200 g load, ": 300 g load "Cellophane" is a Registerd Trade Mark The invention is illustrated by the following Examples.

Examples 1 to 17 To each of pressure sensitive adhesive components blended as shown in Table 3, was added a mixed solvent with n-hexane and toluol mixed in a ratio of 1:1, in a composition concentration of 15%. The solutions were coated in a conventional method on basic films and dried to obtain adhesive tapes. The adhesive strengths and self-adhesive strengths were then determined. The results are shown in Table 3.

Table 3 Example No. 1 2 3 4 5 6 7 8 Elastomer Butyl rubber 100 100 100 100 100 100 100 Polyisoprene rubber 50 50 50 100 Natural rubber Polymer Polyisoprene 10 20 30 40 20 20 40 20 Polybutene Thickener Polyterpene 20 20 20 20 20 10 10 10 Rosin-ester resin Thickness of the adhesive tape 54 55 56 57 59 58 58 57 Gu) Adhesive strength (9/24 mm width) 400 490 500 570 640 580 610 230 Self-adhesive strength 1020 1140 1160 1160 1410 1450 1160 1930 (9/24 mm width) Initial adhesive strength 420 450 510 510 560 530 530 400 (9/5 mm diameter) Example No. 9 10 11 12 13 14 15 16 17 Elastomer Butyl rubber 100 100 100 100 100 50 75 80 Polyisoprene 100 50 50 50 25 35 Rubber Natural rubber 25 25 15 Polymer Polyisoprene 40 20 20 10 20 30 20 5 Polybutene 10 30 10 30 10 Thickener Polyterpene 10 10 20 10 10 10 5 Rosin-ester resin 10 10 10 5 20 Thickness of the adhesive tape (it) 59 60 60 59 59 59 58 60 60 Adhesive strength 550 510 480 550 650 610 540 340 660 (9/24 mm width) Self-adhesive strength (9/24 mm width) 1280 1160 1180 1260 1450 1250 1300 1200 1600 Initial adhesive strength (9/5 mm diameter 510 470 510 520 550 520 420 340 540 Examples 18 to 31 On one side of polypropylene film having a thickness of 40 , were coated the various adhesive compositions shown in Table 4 and dried to obtain adhesive tapes with adhesive layers having a thickness of 20 y. The properties of the tapes were then measured. The results are shown in Table 4.

Table 4 Example No. 18 19 20 21 22 23 24 Elastomer SIS 100 100 100 90 90 90 90 SBS 10 NR 10 isobutylene 10 butyl rubber 10 Thickener (50) (50) (50) (60) (60) (60) (60) polyterpene rosin-ester petroleum resin 50 50 50 60 60 60 60 Additives (50) (50) (50) (60) (60) (60) (60) CaCO3 50 titanium oxide 50 mineral and vegetable oil and modified one 40 50 50 50 50 thereof polyterpene 50 10 10 10 10 Properties initial adhesive property 600 500 500 300 700 500 700 (9/5 mm diameter) adhesive property 600 650 700 500 600 550 500 (9/20 mm width) self-adhesive property 2000 1600 1700 2000 1800 1800 1 700 (9/20 mm width) self-adhesion keeping property 0 0 0 0 0 0 0 (mm/20 mm.h.500 9) Table 4 (Cont.) Example No. 25 26 27 28 29 30 31 Elastomer SIS 100 100 100 100 100 100 100 SBS NR isobutylene butyl rubber Thickener (60) (60) (50) (80) (100) (30) (40) polyterpene 60 rosin-ester 10 petroleum resin 50 50 80 100 30 40 Additives (50) (50) (50) (100) (120) (60) (O) CaCO3 10 60 titanium oxide 20 mineral and vegetable 40 40 30 80 1 20 oil and modified one thereof polyterpene 10 10 10 Properties initial adhesive property 700 700 600 510 410 700 300 (9/5 mm diameter) adhesive property 600 600 600 440 520 650 650 (9/20 mm width) self-adhesive property 1800 2000 2000 2300 1850 2000 1 500 (g/20 mm width) self-adhesion keeping 0 0 0 0 0 0 0 property (mm/20 mm.h.500 9) Example 32 On a polyester film having thickness of 25 , was coated a composition shown in Table 4, and then dried to obtain an adhesive tape having an adhesive layer with a thickness of 25 IL The properties of the obtained tape are shown in Table 5.

Example 33 On an unplasticised PVA film, was coated an adhesive composition shown in Table 4, and dried to obtain an adhesive tape having an adhesive layer with a thickness of 20 IL. The properties of the tape are shown in Table 5.

Table 5 Example No.

32 33 Adhesive Composition SIS 100 100 Petroleum resin 50 50 Polyterpene 10 CaCO3 10 Titanium oxide 50 Mineral and vegetable oil and modified oil thereof 30 Properties Initial adhesive strength 500 600 (9/5 mm) Adhesive strength 600 500 (9/20 mm) Self-adhesive strength 1,600 1,500 (9/20 mm) Self-adhesion keeping 0 0 property (mm/500g.hr) Example 34 Two kinds of adhesive tapes were prepared by coating the adhesive composition on polypropylene films as shown in Table 6.

Using the tapes, two bundles of spinach, having a weight of 250 g each, were tied up with a self-bonding length between tape ends of 1 7 mm. Immersing the bundle of spinach into water, the length of the self bonded parts of the tapes which peeled off in the course of time were then measured. The results are shown in Table 6.

Table 6 Composition Elastomer SIS 100 parts Thickener (Quintone A- 100) 30 parts Polybutene Additive (Factice) 60 parts Peeling off of the bonding part 70 min. later 0 120 min. later 0 220 min. later 0 1 7 hours later 6 mm

Claims

1. An adhesive tape comprising a water-proof substrate carrying a pressure sensitive adhesive composition comprising 100 parts by weight of elastomer, 5 to 1 50 parts by weight of thickener, 0 to 40 parts by weight of another polymer and 0 to 1 50 parts by weight of additives.

2. A tape according to claim 1 in which the adhesive composition is coated on one side only of the substrate and is a substantially continuous coating.

3. A tape according to claim 1 or claim 2 in which the coating has a dry thickness of 5 to 30 microns.

4. A tape according to any preceding claim in which the waterproof substrate is selected from polypropylene film, polyethylene film, unplasticised PVA film and polyester film.

5. A tape according to any preceding claim in which the elastomer is selected from natural rubber, butyl rubber, polyisoprene rubber, a styrene butadiene block copolymer and a styrene isoprene block copolymer.

6. A tape according to any preceding claim in which the said other polymer is present and is selected from polyisoprene having a molecular weight of 7,000 to 20,000 and polybutene having a molecular weight of 1,000 to 10,000.

7. A tape according to any preceding claim in which the thickener is present and is selected from polyterpene, rosin ester and petroleum resin.

8. A tape according to claim 7 in which the thickener comprises a petroleum resin selected from synthetic polypeptene, alicyclic resin, hydrogenated hydrocarbon resin, unsaturated hydrocarbon resin and isoprene hydrocarbon resin.

9. A tape according to any preceding claim including at least one additive selected from calcium carbonate, zinc oxide, titanium oxide, vegetable oil, mineral oil, modified vegetable oil, paraffinic or aromatic process oil, polybutene, liquid polyisobutylene or polyterpene having a softening point of at least 20"C.

10. A tape according to any preceding claim in which the adhesive composition comprises elastomer selected from butyl rubber, polyisoprene rubber and natural rubber, other polymer selected from polyisoprene and polybutene, and thickener selected from polyterpene and rosin ester rubber.

11. A tape according to any preceding claim in which the adhesive coating will bond firmly to itself substantially without creep and will bond with a peelable bond to flowers or vegetables.

1 2. A tape according to any preceding claim having an adhesive strength of 100 to 700 g per width of 20 mm and a self-adhesive strength above 900 g per width of 20 mm.

1 3. A tape according to any preceding claim substantially as herein described.

14. A pressure sensitive adhesive composition suitable for use in tape according to claim 1 and which comprises 100 parts by weight of elastomer, 5 to 1 50 parts by weight of thickener, O to 40 parts by weight of another polymer and 0 to 1 50 parts by weight of additive.

1 5. A composition according to claim 14 in which the elastomer is selected from natural rubber, butyl rubber, polyisoprene rubber, a styrene butadiene block copolymer, and styrene isoprene block copolymer.

1 6. Adhesive according to claim 14 or claim 1 5 which contains, as the other polymer, a polymer selected from polyisoprene having a molecular weight of 7,000 to 20,000 and polybutene having a molecular weight of 1,000 to 10,000.

17. A composition according to any of claims 14 to 16 containing, as the thickener, a thickener selected from polyterpene, rosin ester and petroleum resin.

1 8. A composition according to claim 1 7 in which the petroleum resin is selected from synthetic polypeptene, alicyclic resin, hydrogenated hydrocarbon resin, unsaturated hydrocarbon resin and isoprene hydrocarbon resin.

19. A composition according to any of claims 14 to 18 containing, as the additive, additive selected from calcium carbonate, zinc oxide, titanium oxide, vegetable oil or modified vegetable oil, paraffinic or aromatic process oil, polybutene, liquid polyisobutylene or polyterpene with a softening point of at least 20"C.

20. A bundle of vegetables or flowers held together by tape according to any of claims 1 to 1 3 which is bonded releasably to the flowers or vegetables, without damage to them, and is held firmly with a creep resistant bond by adhesion between overlapping faces of the adhesive coating.