GB2058610A

GB2058610A - Pressure sensitive adhesives and tapes

Info

Publication number: GB2058610A
Application number: GB8022843A
Authority: GB
Original assignee: Nichiban Co Ltd
Current assignee: Nichiban Co Ltd
Priority date: 1979-07-13
Filing date: 1980-07-11
Publication date: 1981-04-15
Also published as: JPS6245273B2; DK299380A; IL60011A0; FR2460984A1; CA1142038A; DE2954420C2; IT7924793A0; NZ191167A; SE7909765L; GB2058610B; DK153565C; ES482906A1; JPS5626968A; NO794055L; DE2954239C2; GB2057916A; IL60011A; BE884284A; DE2930554C2; DK153565B

Abstract

Pressure sensitive tapes are provided in which the adhesive coating is one that will bond firmly to itself but will bond with a peelable bond to the goods packaged within it. The tapes are particularly useful for packaging vegetables and flowers. The adhesive composition itself is generally new, and is generally based on an elastomer including styrene isoprene block copolymer and containing also thickeners and optionally other additives.

Description

1 1

SPECIFICATION Pressure sensitive adhesives and tapes

GB 2 058 610 A 1 It is known to tie bundles of vegetables or flowers 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 s, ibstrate 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 lengths 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 10 surface. When tying a bundle the tape is cut to length and the ends are overlapped and the overyiing 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 ot flowers or other goods are held together by the tightness of the 15 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 sufficiently strongly to prevent this it is liable to damage the goods being packaged.

According to the invention a pressure sensitive tape comprises a substrate carrying an adhesive composition and has an adhesive strength as herein defined of below 700, generally 100to 700, and a 20 self-adhesive strength as herein defined above 900, and generally above 1500. Generally it has a self adhesion keeping strength as herein defined of 0 to 7 and preferably it has an initial adhesive strength as herein defined of 200 to 700. It is particularly preferred that the tape should have a self-adhesive strength above 1500, for instance 1500 to 2500, 3000 or even up to 4000.

Although pressure sensitive tapes having, individually, properties within one or more of the ranges 25 defined above are known the known tapes do not comply with the combinations of properties defined above, especially with combinations in which the self-adhesive strength is above 1500. An advantage of the tape of the invention is that it 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 30 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 a substantially continuous coating on one side 35 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 40 will remain as a tight wrapping around the goods at all times.

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 11-11 of Figure 1.

Figure 3 is an explanatGry 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 Figure 1, from which lengths are cut of the size necessary for packaging the desired bundle of vegetables or other goods 4, as 50 shown in Figure 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 55 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 60 preferably has a thickness of from 20 to 60 microns but other thicknesses can be used.

Several pressure sensitive adhesive compositions can be formulated that will give the defined novel combination of properties. A preferred composition, which itself forms a further part of the invention, comprises 100 parts by weight of elastomer and 5 to 150 parts by weight of a thickener, and 2 GB 2 058 610 A 2 at least 50% by weight of the elastomer is styrene-isoprene block copolymer. Preferably most e.g. at least 80% and often at least 90% by weight, or all of the elastomer is the stated block copolymer.

The elastomer must comprise or consist of styrene isoprene block copolymer. This can also be referred to as styrene-isoprenestyrene block copolymer. The ratio of styrene and isoprene is preferably 10:90 to 25:75, most preferably 13:87 to 22:78. Suitable materials are sold by Shell Chemicals under the trade name Kraton, for instance Kraton 1107, XIII and DE 1112 which have styrene isoprene ratios respectively of 14:86, 21:79 and 14:86 and which may have a molecular weight of 150000, and by Philips Petroleum under the trade name Solprene 418, this having a molecular weight of 3000000 and a styrene isoprene ratio of 15:85. Other elastomers that may be included with the styrene isoprene block copolymer include natural rubber, synthetic rubber such as Butyl rubber (for example, Butyl No. 10 268, Esso Standard Petroleum Co.), polyisoprene rubber and styrenebutadiene block copolymer. Mixtures may be used.

For thickener, polyterpene, rosin ester and petroleum resins are preferred. The thickener component may alternatively be described as a tackifier. Preferred commercially available thickeners, include polyterpene having a softening point of 1 OOOC or more, rosin ester and petroleum resin. For 15 example polyterpene such as Quintone A 100, D 100, D 200, C 100, C 200 S of Japan Geon Co. Ltd., alicyclic hydrocarbon such as Arcon P 100. P 115, P 125 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 1202 of Esso Chemical Co. and hydrocarbon resin such as Tack-Ace 20 A 100 of Mitsui Petroleum Chemical Co. Ltd. Mixtures may be used, The use of the thickener outside the range of 5 to 150 parts per 100 parts elastomer lowers the seif- adhesiveness and creep resistance and adversely influences the capacity of a tape for tying. The preferred amount is 30 to 100 parts.

Other additives 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 (for instance castor oil, coiza oil, soybean oil and Factice), paraffinic or aromatic process oil (for example, Flexon 765, 110, 112 and 876 of Esso Chemical Co.), polybutene, liquid polyisobutylene or polyterpene having a softening point of 201C or higher may be used. When using the additive in an amount over 150 parts by weight, cohesiveness and self-adhesiveness may be ill-balanced, and result in a bad initial adhesivity and make the instantaneous strong bond unsure. Any liquid additives that 30 remain in the adhesive coating are preferably used in an amount of 20 parts by weight or less in order to gain a balanced cohesiveness.

Instead of using adhesive compositions as defined above in which at least 50% by weight of the elastomer is styrene-isoprene block copolymer other compositions can be formulated for providing tapes according to the invention, although these other compositions will generally be less satisfactory.

They will again generally contain 5 to 150 parts by weight of a thickener, for instance as discussed above, and 100 parts by weight of elastomer. The elastomer will contain less than 50%, and generally will be free of, styrene isoprene block copolymer. Broadly it may be selected from any of the elastomers discussed above but is preferably polyisoprene rubber, although elastomers such as natural rubber, synthetic rubber or styrene butadiene block copolymer or mixtures may also be used. Preferably 40 the compositions are free of curing agents such as phenolic materials or isocyanates or formaldehyde based materials. With such elastomers it may be desirable to include other polymers in amounts of up to 40 parts. Suitable polymers are polyisoprene or polyisobutylene (each of molecular weight of about 7,000 to 20,000) or polybutene (molecular weight of about 1,000 to 10, 000).

In order to apply the compositions onto the substrate the compositions are made up into coatable 45 compositions by inclusion of suitable organic diluents, usually aliphatic or aromatic hydrocarbons containing less than 10 carbon atoms, e.g. hexane or toluene. The amount of diluent is typically 60 to 90%, preferably 70 to 80%, by weight of the composition.

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 ju 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 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 surface only, can easily be cut to length and mechanically tied from a roll as shown in Figure 1 and thus it is necessary to pre-cut the tape.

It is easily possible to formulate adhesive compositions for use in the invention and tapes coated 60 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.

3 GB 2 058 610 A 3 To define the various bonding strengths more accurately we define below precise tests that may be used for measuring these.

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 201C under a relative humidity of 65%. The initial adhesive strength is the peeling resistance 5 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 1801. The adhesive strength is the peeling resistance obtained by peeling 10 off the tape at a peeling velocity of 300 mm per minute. The method is conducted according to ASTM or JIS-Z 1522.

To measure self-adhesion a 15 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- 15 adhered end of the tape at an angle of 1800 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 201C and a relative humidity of 65%. The extension in mm after an hour 20 is measured and is recorded as the self-adhesion keeping strength and is an indication of the creep resistance of the adhesive composition.

The invention includes not only the described tapes and the adhesive compositions, especially those containing styrene isoprene block copolymers, but also includes bundles of vegetables or flowers bonded releasably by the tape but with overlapping faces of the tape both coated with the adhesive and 25 providing a secure bond.

The invention is illustrated by the following examples.

EXAMPLES 1 TO 14 On one side of polypropylene film having a thickness of 40 1A were coated the various adhesive compositions shown in Table 1 and dried to obtain adhesive tapes with adhesive layers having a thickness of 20 ju. Each composition was coated from a composition containing 85% of a 1:1 mixture of n-hexane and toluol. The properties of the tapes were then measured. The results are shown in Table 1.

In the table SIS represents styrene isoprene block copolymer (for instance Kraton 1107) SBS represents styrene butadiene copolymer and NR represents natural rubber.

GB 2 058 610 A 4 TABLE 1

Example No. 1 2 3 4 5 6 7 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) CaCO, 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 (g /5 min diameter) adhesive property 600 650 700 500 600 550 500 (g /20 min width) self-adhesive property 2000 1600 1700 2000 1800 1800 1700 (g 120 min width) self-adhesion keeping property 0 0 0 0 0 0 0 (mm /20 mm.h. 500 g) X GB 2 058 610 A 5 TABLE 1 (Continued) Example No. 8 9 10 11 12 13 14 Elastomer SIS 100 100 100 100 100 100 100 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) (0) CaCO, 10 60 titanium oxide 20 mineral and vegetable oil and modified one 40 40 30 80 120 thereof polyterpene 10 10 10 Properties initial adhesive property 700 700 600 510 410 700 300 (g /5 mm d i ameter) adhesive property 600 600 600 440 520 650 650 (g 120 mm width) self-adhesive property 1800 2000 2000 2300 1850 2000 1500 (g /20mrnwidth) self-adhesion keeping property 0 0 0 0 0 0 0 (mm 120 mm. h. 500 g) EXAMPLE 15

On a polyester film having thickness of 25 M, was coated a composition shown in Table 2, and then dried to obtain an adhesive tape having an adhesive layer with a thickness of 25 M. The properties of the obtained tape are shown in Table 2.

EXAMPLE 16

On an unplasticised PVC film, was coated an adhesive composition shown in Table 2, and dried to obtain an adhesive tape having an adhesive layer with a thickness of 20 M. The properties of the tape are shown in Table 2.

6 GB 2 058 610 A TABLE 2

Example No.

16 Adhesive Composition SIS 100 100 Petroleum resin 50 50 Polyterpene 10 CaC03 10 Titanium oxide 50 Mineral and vegetable oil and modified oil thereof 30 Properties Initial adhesive strength (g 15 mm) 500 600 Adhesive strength (g 120 mm) 600 500 Self-adhesive strength (g /20 mm) 1,600 1,500 Self-adhesion keeping property (mm / 500 g. hr.) 0 0 EXAMPLE 17 Two kinds of adhesive tapes were prepared by coating the adhesive composition on polypropylene film as shown in Table 3. 5 Using the tapes, two bundles of spinach, having a weight of 250 g each, were tied up with a selfbonding length between tape ends of 17 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 3.

TABLE 3

X Composition SIS 100 parts Thickener (Quintone A-100) 30 parts Additive (Factice) 60 parts Peeling off of the bonding part min. later 0 min. later 0 220 min. later 0 17 hours later 6 mm 7 EXAMPLE 18

GB 2 058 610 A 7 The compositions shown in Table 4 were coated onto tapes as in Example 1 and their properties are recorded in Table 4.

TABLE 4

Example No. 5 6 8 13 15 17 Elastomer Butyl rubber 100 100 100 50 80 Polyisoprene rubber 100 25 25 Natural rubber 25 15 Polymer Polyisoprene 20 20 20 20 20 5 Polybutene 10 Thickener Polyterpene 20 10 10 10 10 5 Rosin-ester resin 10 20 Thickness of the adhesive tape (g) 59 58 57 59 58 60 Adhesive strength (g 124 mm width) 640 580 230 650 540 660 Self-adhesive strength (9 124 mm width) 1410 1450 1930 1450 1300 1600 Initial adhesive strength (g 15 mm diameter) 560 530 400 550 420 540

Claims

1. A pressure sensitive tape comprising a substrate carrying a pressure sensitive adhesive composition such that the tape has an adhesive strength as herein defined below 700 and aselfadhesive strength as herein defined above 900.

2. A tape according to claim 1 which has a self-adhesive keeping strength as herein defined of 0 to 7.

3. A tape according to claim 1 or claim 2 in which the self-adhesive strength rs above 1500. 10

4. A tape according to claim 3 in which the self-adhesive strength is 1500 to 3000.

5. A tape according to any preceding claim comprising a waterproof substrate coated on one side only with a substantially continuous coating of the adhesive composition.

6. A tape according to any preceding claim in which the composition is present as a coating having a dry thickness of 5 to 30 microns.

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

8. A tape according to any preceding claim in which the composition comprises 100 parts by weight of elastomer and 5 to 50 parts by weight thickener and in which at least 50% by weight of the elastomer is styrene isoprene block copolymer.

9. A tape according to claim 8 in which at least 90% by weight of the elastomer is styrene isoprene block copolymer.

10. A tape according to claim 8 or claim 9 in which the thickener is selected from polyterpene, rosin ester and petroleum resin.

11. A tape according to claim 10 in which the thickener comprises petroleum resin selected from25 8 GB 2 058 610 A 8 synthetic polypeptene, alicyclic resin, hydrogenated hydrocarbon resin, unsaturated hydrocarbon resin and isoprene hydrocarbon resin.

12. A tape according to any of claims 1 to 7 in which the adhesive composition comprises 100 parts by weight of elastomer and 5 to 50 parts by weight thickener and in which the elastomer 5 comprises polyisoprene rubber, butyl rubber, natural rubber or mixtures thereof.

13. A tape according to claim 12 in which the composition also comprises up to 40 parts of a polymer selected from polyisoprene having a molecular weight of 7000 to 20000 and polybutene having a molecular weight of 1000 to 10000.

14. A tape according to any of claims 8 to 13 in which the composition contains up to 150 parts by weight of an additive selected from calcium carbonate, zinc oxide, titanium oxide, vegetable oil, 10 mineral oil, modified vegetable oil, paraffinic or aromatic process oil, polybutene, liquid polisobutylene or polyterpene having a softening point of at least 201C.

15. A tape according to claim 1 substantially as herein described with reference to any of the Examples.

16. A bundle of vegetables or flowers held together by tape according to any preceding claim and 15 which is bonded releasably to the flowers orvegetables without damage to them and is held firmly with a creep resistant bond by adhesion between overlapping faces of the adhesive coating.

17. A pressure sensitive adhesive composition comprising 100 parts by weight of elastomer and 5 to 50 parts by weight thickener and in which at least 50% by weight of the elastomer is styrene isoprene block copolymer.

18. A composition according to claim 17 in which at least 90% by weight of the eiastomer is styrene isoprene block copolymer.

19. A composition according to claim 17 or claim 18 in which the thickener is selected from polyterpene, rosin ester and petroleum resin.

20. A composition according to claim 19 in which the thickener has a softening point of 1 OOOC or more and comprises petroleum resin selected from synthetic polypeptene, alicyclic resin, hydrogenated 45 hydrocarbon resin, unsaturated hydrocarbon resin and isoprene hydrocarbon resin.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1981. Published by the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.

20. A composition according to claim 19 in which the thickener comprises petroleum resin 25 selected from synthetic polypeptene, alicyclic resin, hydrogenated hydrocarbon resin, unsaturated hydrocarbon resin and isoprene hydrocarbon resin.

2 1. A composition according to any of claims 17 to 20 and which contains up to 150 parts by weight of an 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 30 polyterpene having a softening point of at least 201C.

22. A composition according to claim 17 substantially as herein described with reference to any of the Examples.

23. Pressure sensitive tape coated with a composition according to any of claims 17 to 22.

New claims or amendments to claims filed on 7th January 1981 Superseded claims 11 17 and 20 New or amended claims:- 11. A tape accordifig to claim 10 in which the thickener has a softening point of 1 OOOC or more and comprises petroleum resin selected from synthetic polypeptene, alicyclic resin, hydrogenated 40 hydrocarbon resin, unsaturated hydrocarbon resin and isoprene hydrocarbon resin.

17. A pressure sensitive adhesive composition comprising 100 parts by weight of elastomer and 5 to 150 parts by weight thickener and in which at least 50% by weight of the elastomer is styrene isoprene block copolymer.