WO2000039231A1

WO2000039231A1 - Release coating composition

Info

Publication number: WO2000039231A1
Application number: PCT/EP1999/010400
Authority: WO
Inventors: Jos Willekens; Jozef Keustermans
Original assignee: Avery Dennison Corporation
Priority date: 1998-12-23
Filing date: 1999-12-22
Publication date: 2000-07-06
Also published as: AU3043900A; GB9828654D0

Abstract

The invention relates to release coatings used to provide certain adhesive qualities for adhesives adhering thereto. The release coating includes an additive, such as a polydimethyl siloxane, or derivative thereof. The additive alters the adhesion of an adhesive to other substrates after having been brought into contact with the release coating.

Description

RELEASE COATING COMPOSITION

The present invention relates to a release coating, in particular, but not exclusively, for a laminate with a pressure sensitive adhesive coating and/or for self wound pressure sensitive adhesive tapes.

Release coatings are commonly used where the adhesion of an adhesive needs to be altered against a particular substrate or part thereof. Often the adhesive will be a pressure sensitive adhesive (PSA) and in which case the release coating is generally made from a low surface tension coating. The low surface tension coating is usually silicone based.

Release coatings are often used on laminated adhesive tapes, for example as used in the diaper industry. Often a laminated tape construction will require the adhesive in one part of the tape to be aggressive to form a reliable fixing, whereas adjacent part of the tape will require the adhesive to be less aggressive so that the end user can readily peel back the tape portion as often as necessary. One instance where this problem occurs is in re-closeable fasteners for diapers where one edge of the tape forms a hinge portion which must not separate in use and the other part of the tape forms the resealable tab for keeping the diaper closed.

In view of the conflicting requirements for the adhesive in the tape various compromises must be reached in the nature of the adhesive. One compromise solution has been to use an adhesive with lower tack than ideal for the hinge portion over the entire tape. Another previous solution has been to use different types of adhesives in different parts of the tape, namely a aggressive adhesive in the hinge region and a less aggressive adhesive on the resealable tab portion. However this latter solution greatly increases the cost of production of the tape.

The present invention seeks to provide a release coating suitable for use with laminated adhesive tapes and other constructions.

According to a first aspect of the present invention there is provided a release coating composition comprising a release coating composition curable to form a release coating matrix and a free silicone oil additive having a molecular weight of at least 1000 and/or a viscosity of at least 10 cSt. The release coating composition of the present invention includes the free silicone oil additive, which additive can effect the performance of an adhesive brought into contact with the release coating composition. Normally the free silicone oil will reduce the tack of the adhesive in contact with the release coating.

Preferably the free silicone oil is a siloxane of the general formula:

(X or R)-SiR₂-0-(Si(R₂)-0)_a-0-(Si(RX)-0)_b-(Si{RY))-0)_c -SiR₂-(X or R) where X is selected from the group consisting of: alkyl; alkenyl; hydrogen; hydroxide; amino; epoxy; carbonyl; and halide; and where Y represents a polysiloxane branching of the main poiysiloxane chain, which may contain organic functionality like X located on - or at the end of this side chain; and where a, b and c are independent integers, c is greater than or equal to 0, b is greater than or equal to 0 and a is greater than 0.

In situations where the free silicone oil additive can participate in the curing of the release coating component, it is important that sufficient additive is added so that the required amount of free silicone oil additive remains in the cured composition to have the required effect upon the adhesive properties of an adhesive. Preferably, the silicone oil additive will not participate in the curing of the release coating component. In any case the amount of free additive after curing will be greater than 3 parts by weight of the total weight of the coating, and preferably will be in the range of 5 parts to 10 parts by weight of the total weight of the coating.

Advantageously the release coating component may be any of the normal species which are cured to form a release coating such as curable silicones or carbamides, as known to those skilled in the art.

The free silicone oil additive preferably has a molecular weight of greater than 5000. The free silicone oil additive is advantageously a liquid and thus normally has a molecular weight of less than 1 ,000,000. The free silicone oil additive should preferably comprise at least 3 parts by weight of the cured release coating composition and for optimum performance 6 to 8 parts by weight of the free silicone oil component is preferred.

According to a second aspect of the present invention, there is provided an adhesive construction comprising a generally planar release substrate and a generally planar fastening substrate, where a first surface of the release substrate is juxtaposed to a first surface of the fastening substrate with an adhesive sandwiched therebetween, wherein a release portion of the first surface of the release substrate is coated with a release coating so that the opposed portion of the fastening substrate with the associated adhesive is peelable from the release portion, the release coating composition including an additive which alters the tackiness of the adhesive.

This adhesive construction can be used advantageously in laminated tapes and in sheets of self-adhesive label construction. Preferably the adhesive construction comprises the release coating composition according to the first aspect of the invention.

The release substrate and the fastening substrate will normally be formed from polypropylene, polyethylene, other suitable plastics material or from paper. The film may also be a co-extruded or multilayer film. The release substrate need not be the same as the fastening substrate in any particular embodiment. When the adhesive construction forms a laminated tape, such as a diaper tape, it is preferred for the release substrate to be formed from a plastics material. On the other hand, when the adhesive construction forms a label construction, it is preferred for the release substrate to be formed from a paper material. The paper material may be coated.

In a laminated tape construction, the release substrate is preferably also coated on its other side with an adhesive. In contrast, the proposed opposite side of the fastening substrate is not normally covered on its opposite side with an adhesive.

In a label construction, no adhesive is normally coated on the other side of the fastening substrate or the release substrate.

Preferably the adhesive or adhesives is a pressure sensitive adhesive. Any pressure sensitive adhesive composition known in the art can be utilized. Such adhesive compositions are described in, for example, "Adhesion and Bonding", Encyclopedia of Polymer Science and Engineering vol. 1 , pages 476-546, Interscience Publishers, Second Edition 1985. Such compositions generally contain an adhesive polymer such as a natural, reclaimed or styrene-butadiene rubber, styrene butadiene or styrene isoprene block copolymers, polyisobutylene, poly (vinylether) or poly (acrylic) ester as a major constituent. The pressure sensitive adhesive may be a blend of components. Other materials may be included in the pressure sensitive adhesive composition such as resin tackifiers including, for example aliphatic hydrocarbon resin, mixed aliphatic/aromatic resins, rosin esters, rosin acids, polyterpenene or terpene phenolic resins; antioxidants; plasticizers such as mineral oil or liquid polyisobutylenes; and fillers such as zinc oxide or hydrated alumina. The selection of pressure sensitive adhesive to be used in any particular multi layer article or construction is not critical to this invention, and those skilled in the art are familiar with many suitable pressure sensitive adhesives.

For adhesive tape construction, commercially available plastic films such as cast polypropylene mono and bi-orientated polypropylene (BOPP), polyethylene, PVC, polyester film and copolymer films are all suitable for use as a substrate. Paper substrates on which the above plastics materials have been extruded are also suitable, and also paper and coated paper are suitable, e.g. glassine, coated paper such as clay coated paper, machine glazed, or super calendared craft paper. The calliper of such material can be between 20 and 300 micron or higher, but this is not critical to the present invention. For label construction, the same materials may be used, but it is presently preferred to use paper or coated paper material.

Although the invention is particularly applicable to adhesive tapes and label constructions, the invention is equally application to other applications where a release coating or backing substrate is used.

According to a third aspect of the present invention there is provided a method for producing a release substrate with a release coating composition where the release coating composition includes an additive which effects the tack of adhesives brought into contact with the release coating composition, e.g. in a controlled and desired manner.

Preferably, the release coating composition is applied to only selected portions of the release substrate.

Advantageously, the method will be used to produce multilayered article where an adhesive layer overlies the release substrate including the area covered with the release coating composition.

Preferably the adhesive is sandwiched between the release substrate and a fastening substrate.

The method preferably includes the step of curing the release coating composition when on the release substrate. The coating may be cured by actinic radiation, temperature or combination thereof. The method will advantageously adopt the release coating composition according to the first aspect of the invention and will be preferably used to form the constructions of the second aspect of the invention.

Normally the total weight of the release coating used in the invention will be around 100 parts by weight, e.g. between 80 and 130 parts by weight, or preferably 100 and 120 parts by weight. Preferably the total weight will be 100 parts by weight and the use of the term 'parts by weight' in this application may be replaced in each case by the term '% by weight'.

The invention will now be described with reference to the accompanying drawings, in which:

Fig. 1 illustrates a cross-section through a first tape construction according to a preferred embodiment of the invention;

Fig. 2 illustrates a cross-section through a second tape construction according to another preferred embodiment of the invention;

Fig. 3 illustrates a label construction according to a third preferred embodiment of the invention;

Fig. 4 illustrates a diaper incorporating the tape of Fig. 1 ;

Fig. 5 shows a cross sectional view along the line 5-5 of Fig. 4;

Fig. 6 illustrates the effect on tack of PDMSs of different molecular weight.

The present invention concerns a release coating composition which contains an additive which alters the adhesive qualities of an adhesive brought into contact with the release coating composition. Fig. 1 shows a tape construction according to a first preferred embodiment of the invention. A release substrate 10 is generally planar. Over part 1 2 of the width of a upper side of the release substrate 10 a release coating 16 is provided. The opposite side of the release substrate 10 is covered with a layer of a release adhesive 18 formed of a pressure sensitive adhesive.

A fastening substrate 20 is generally planar and is provided with a layer of adhesive 22 over the complete width of a lower side of the fastening substrate 20. The layer of adhesive 22 is in face-to-face contact with the upper side of the release substrate 10. Over the opposite side of the fastening substrate 20 a fastening tape release coating 24 is provided.

The adhesive 22 sandwiched between the fastening substrate 20 and the release substrate 10 in the area 14 of the release substrate 10 with the release coating 16 forms a hinge region 26 of the tape construction. A fingerlift tab 28 is provided at the edge of the tape construction distal from the hinge portion 26. The fingerlift tab 28 is provided to allow a user to initiate separation of the fastening substrate 20 with the fastening adhesive 22 from the part 12 of the release substrate 10 coated with the release coating 16.

The substrates 10, 20 may be formed from commercially available plastic films such as cast polypropylene, mono and bi-orientated polypropylene, polyethylene, PVC polyester film or copolymer films. Paper or paper substrates on which the above plastics materials have been extruded are also suitable. The calliper of such material can be between 20 and 300 micron or higher, but this is not critical to the present invention. The two substrates 10, 20 may be formed from different materials. In the preferred embodiment of Fig. 1 a plastics material is normally used.

The release coating 16 comprises a cured component onto which cured component the fastening tape adhesive 22 has lower adhesion than to the release substrate 10. The cured component may be any of the normal species which are cured to form a release coating such as curable silicones, carbamides. Presently, it is preferred if the release coating component comprises linear polydimethyl siloxane (PDMS).

The method of curing the release coating 1 6 will be selected depending upon the constituents which are cured to form the cured component. The curing technique will normally be selected from actinic radiation, temperature or a combination thereof. The cured component will normally be a cured silicone release coating or sometimes a carbamide release coating. Suitable coatings are well known in the art.

A silicone based release coating is made up of several ingredients which will cure after exposure to thermal or actinic radiation, or some combination thereof. The curing will normally take place on the substrate upon which it is coated and thus render the substrate adherent.

A major proportion of the release coating is typically a functionalized polysiloxane or mixture of functionalized polysiloxanes of the general form:

(X or R)-SiR₂-0-(Si(R₂)-0)_a-(Si(RX))-0)_b-SiR₂-(X or R)

where X represents a functionality described below, a and b are independent integers, b is greater than or equal to 0 and a is greater than 0.

A typical thermal curing composition, irrespective of the mechanism, would be formed from a polymer, a crosslinking agent, a catalyst and optionally, solvent, anchorage additive, release modifier.

For the base polymer, the values of a and b depend on whether it is a solventless or solvent based system. As the emulsion system is typically derived from either the solventless or solvent based system its a and b values are within the same ranges. In a very general sense, for solventless silicone systems a and b is typically between 50 ad 200, and for solvent based systems the range is between 3000 and 1 2,000. Also, the polymers are typically described in terms of viscosity where in solventless systems the viscosity is less than about 1000 centipoise and in solvent systems the viscosity can be as high as 10,000,000 centipoise. In the present invention a solventless silicone system has been shown to incorporate the additive with advantageous effect.

For thermal curing silicone based release compositions, two curing mechanisms are known: addition cure (or hydrosilylation) and condensation cure.

In the case of addition cure (or hydrosilylation), the typical reaction is a precious metal (complex of (Group VIII metal) platinum, rhodium, palladium, osmium, iridium or ruthenium) or chloroplatinic acid catalyzed crosslinking reaction between a vinyl or alkenyl functionalized polydimethylsiloxane and a trimethylsilyl chainstopped polymethylhydrogensiloxane homo- or co-polymer. The composition may be solventless, solvent based or emulsion based. An inhibitor is typically included in the coating composition to extend the workable shelf-life of the complete coating composition or to avoid the problems of premature gelling or curing of solventless or emulsion based composition. The composition may also include a release modifier which is typically a functionalized MQ type silicone resin. Optionally, the composition may contain an organic solvent such as heptane, toluene, mineral spirits, methyl ethyl ketone and the like to facilitate handling and coating of high molecular polymers.

Therefore, typically,

X = vinyl or alkenyl for the polysiloxane base polymer

X = H for the crosslinking agent

R = monovalent hydrocarbon radical free of unsaturation such as methyl, ethyl propyl, butyl and the like. Most common is where R = methyl.

In the case of condensation cure, the typical reaction is a tin or zinc ester catalysed reaction between a hydroxyl terminated polydimethylsiloxane and a trimethylsilyl chainstopped polymethylhydrogensiloxane homo- or co-polymer. The composition may be either solvent based or emulsion based. The composition may additionally include an anchorage additive, bath-life extender or release modifier.

Therefore, typically X = hydroxy or alkoxy X = H for the crosslinking agent

A comprehensive overview of thermal curing compositions can also be found in: Converting and Packaging, December 1987, pages 1 52 to 155.

A typical actinic radiation curing composition, irrespective of the mechanism, would be: polymer catalyst and optionally, solvent, anchorage additive, release modifier, sensitiser.

The main radiation curing compositions use polysiloxane polymers where X represents a functionality like acrylate, methacrylate, epoxy, vinylether, vinyl, mercaptan.

Usually there is a organic spacer which connects these function group to the polysiloxane chain.

A comprehensive overview of radiation curing compositions can be found in "Advances in Pressure Sensitive Adhesive Technology", edited by Donatas Satas and published by Van Nostrand Reinhold, chapter 2: "Chemistry and Technology of Radiation Curable Release Coatings" by R.P. Eckberg, page 50 - 75.

An additive is provided in the release coating that alters the adhesive properties of the fastening tape adhesive 22. The effect on the adhesive properties is not limited to when the fastening tape adhesive 22 is in contact with the release coating 16. The additive normally comprises a silicone oil.

A major proportion of the oil composition is typically a non-functionalized polysiloxane or mixture of functionalized polysiloxanes and non-functionalized polysiloxanes of the general form:

(X or R)-SiR₂-0-(Si(R₂)-0)_a-0-(Si(RX)-0)_b-(Si(RY))-0)_c -SiR₂-(X or R)

where Y represents a polysiloxane branching of the main polysiloxane chain, which may contain organic functionality like X located on - or at the end of this side chain. X represents a functionality described below, a, b and c are independent integers, c is greater than or equal to 0, b is greater than or equal to 0 and a is greater than 0.

The total molecular weight of the c branches should be less than the molecular weight of the main polysiloxane chain.

R = monovalent hydrocarbon radical free of unsaturation such as methyl, ethyl propyl, butyl and the like and fluoro substituted alkyl groups. Most common is where R = methyl.

It is preferred that the molecular weight of main polysiloxane chain has to be greater than 1000. Starting at 1000 molecular weight we see an increased detackyfying effect which maximises at about 60 000.

Silicone oil with a molecular weight above 200,000 maintains a significant detackyfication effect up to 1 ,000,000. This is shown in Fig. 6 and Table 1 .

Since the organic substituants X are in almost all cases the most reactive of the functionalised polysiloxane, they should be selected in such manner that they cannot make a stable chemical bond with the reactive substituents of the silicone release formulation, when this is coated and cured.

For example if X = epoxy based and this epoxy polysiloxane is used as a detackyfying additive in a vinyl based platinum catalysed release system which is cured by heat using conditions as used by those skilled in the art, the epoxy polysilicone will not chemically bond to the thermal silicone network. It remains free to migrate or to transfer to the adhesive.

Examples of X may be: alkanyl, vinyl, alkenyl, fluoro, hydroxy, alkoxy, epoxy, acrylate, methacrylate, vinylether, carbinol, functionalised amines, polyurethane.

When R = methyl and X = methyl we have the most versatile material to be used in this invention. This material is generally known as PDMS.

Table 1 shows the effect of silicone oil additives to the finat tack on glass of a pressure sensitive adhesive. This is shown graphically in Fig. 6.

Table 1 demonstrates that low molecular weight (Mr up to 1000) do not significantly affect Finat tack. A progressively greater effort is noted to Finat Tack with increased molecular weight upto Mr = 300,000.

The silicone oil additive should not substantially join in with the crosslinking reaction of the silicone release system in which it has been blended.

In Table 1 , Finat Tack on glass is shown after 1 day adhesive-release coating contact. The release coating contains 10 parts by weight of silicone oil (PDMS fluid) of different molecular weights, all supplied by ABCR GmbH. The release coating is a thermal addition cured silicone formulation, coat weight 1 .5 g/m^ on BOPP. The adhesive is a formulation having a Finat Tack on glass of about 33 N/25mm and formed from a blend of thermoplastic SIS rubber (Kraton, Shell), a solid hydrocarbon resin (Escorez, Exxon), a liquid hydrocarbon resin (Adtac, Hercules) and an anti-oxidant (Irganox, Ciba Geigy). Alternative components are shown in Table 2. The adhesive has an adhesive coat weight of 35g/m².

Table 1

Any pressure sensitive adhesive composition known in the art can be utilized as fastening tape adhesive 22 or release tape adhesive 18. The particular adhesive selected on the specific requirements of the application. Such adhesive compositions are described in, for example, "Adhesion and Bonding", Encyclopedia of Polymer Science and Engineering vol. 1 , pages 476-546, Interscience Publishers, Second Edition 1985. Such compositions generally contain an adhesive polymer such as a natural, reclaimed or styrene-butadiene rubber, styrene butadiene or styrene isoprene block copolymers, polyisobutylene, poly (vinylether) or poly (acrylic) ester as a major constituent. Other materials may be included in the pressure sensitive adhesive composition such as resin tackif iers including, for example aliphatic hydrocarbon resin, mixed aliphatic/aromatic resins, rosin esters, rosin acids, polyterpenene or terpene phenolic resins; antioxidants; plasticizers such as mineral oil or liquid polyisobutylenes; and fillers such as zinc oxide or hydrated alumina. The selection of pressure sensitive adhesive to be used in any particular multilayer article or construction is not critical to this invention, and those skilled in the art are familiar with many suitable pressure sensitive adhesives.

Advantageously, the fastening tape adhesive 22 is selected to be an aggressive adhesive that ensures the hinge portion 26 does not separate in use. The fastening tape adhesive 22 can be selected to be more aggressive than in similar construction previously known due to the release coating additive of the present invention. The tape construction of Fig. 1 may be produced commercially in a particularly

efficient method. An endless line of the release substrate 10 is coated with the release coating 1 6 over part 1 2 of upper side of release tape substrate 10.

Normally, the release coating 16 is cured after application of its constituents to the release substrate 10. The opposite of the release substrate 10 is coated with the pressure sensitive adhesive 1 8.

In a parallel line, an endless line of fastening substrate 20 is coated on its lower side with the fastening tape adhesive 22. The opposite side of the fastening substrate 20 is coated with release coating 24. Fingerlift tab 28 is fitted to one side of the free face of coated layer of fastening tape adhesive 22, though normally this fingerlift tab 28 will be fitted off line.

The two endless lines of substrates 10, 20 are brought into face to face contact of the lower side of the fastening substrate 20 and the upper side of the release substrate 10 with the fastening tape adhesive 22 sandwiched therebetween. Thus is provided a construction with parts of the fastening substrate 20 provided with effectively adhesives having different adhesive properties in an efficient manner.

The tape construction of Fig. 1 will normally then be rolled to form a self wound tape which is then transferred to where the tape is used. The tape construction of Fig. 1 is particularly useful in the diaper industry for forming resealable tabs. The fastening release coating 24, the release tape adhesive 18 and the fingerlift tab 28 may each, singularly or together, be omitted from the tape construction and associated production method if desired. The fastening tape release coating 24 is normally retained if the release tape adhesive 1 8 is provided if the product will be rolled into a self wound tape.

The tape construction of Fig. 1 may be used in the disposable diaper industry to form a releasable tab as shown in Figs. 4 and 5. A disposable diaper 50 is formed with a plastic layer, e.g. of polyethylene, covering the outer surface thereof. Tabs 54 are provided comprising strips of the release tape of Fig. 1 . A landing zone 52 is provided to which the tabs 54 are releasably securable to fit the diaper on a user. The manner in which the tabs 54 is secured to the diaper 50 in the known branching configuration. Examples of this type of mounting are illustrated in WO 96/12464 from which further details may be obtained. In Fig. 4 the left hand tab 54 is shown in the storage position where part of the tab 54 is wrapped around to the unseen surface of the diaper. The right hand tab 54 is deployed for fastening. Fig. 5 shows a cross section through the left hand tab 54.

As shown best in Fig. 5 strips of the tape of Fig. 1 forms tabs 54. Release coating substrate 10 is permanently secured to the diaper shell through adhesive layer 1 8. Fastening substrate 20 is pealably releasable from the release substrate 10 up to the hinge portion 26. The released portion of the fastening substrate 20 has fastening adhesive layer 22 which has been in contact with the release coating 1 6. The released portion of the fastening substrate 20 is releasably securable on the landing zone 52. The tack of the adhesive 22 which has been in contact with the release coating 16 is reduced compared to the tack of the adhesive 22 in the hinge portion. Of course the hinge portion 26 should form a permanent joint as failure would not be acceptable in use of the diaper 50.

An alternative preferred tape construction according to the present invention is shown in Fig. 2 in which the same numerals represent corresponding parts of the constructions. Similar materials may be used in this alternative construction.

Fig. 3 shows a third preferred embodiment of the invention where again the same numeral represent parts of the same general nature as in the embodiments of Fig. 1 and Fig. 2. However, this third preferred embodiment shows a label construction for self adhesive labels. The release substrate 10 will normally be referred to as a 'backing' and the fastening substrate 20 will normally be referred to as a 'face stock'. The requirement of the adhesive will be somewhat different from those required in a diaper tape, but the general requirements are well known to those skilled in the art. The method of controlling the tack of the adhesive 22 through the additive in the release coating 1 6 however is similarly effective in the label construction.

The label construction will not normally have any adhesive layer on the opposite side of the release substrate 20, nor will a release coating be normally applied

to the opposite side of the fastening substrate 20.

EXAMPLES 1 to 21 & COMPARATIVE EXAMPLES 1 & 2

Tape constructions according to Fig. 1 were produced and tested for adhesive properties. The components used for the various layers of the tape construction are shown in Table 2. The components used in the examples and comparative examples are those shown marked with an asterix(*).

The adhesive layer 22 is similar to the adhesive used in the formulations of Table 1 . The formulation has a Finat Tack on glass of about 33 N/25mm and is formed from a blend of thermoplastic SIS rubber (Kraton, Shell), a solid hydrocarbon resin (Escorez, Exxon), a liquid hydrocarbon resin (Adtac, Hercules) and an anti-oxidant (Irganox, Ciba Geigy). The adhesive layer 22 has an adhesive coat weight of 30g/m . The release tape adhesive 18 is similar to the fastening tape adhesive 22.

The release substrate 10 was formed from Bi-orientated polypropylene (BOPP) from UCB. The fastening substrate 20 was formed from cast polypropylene (cast PP) from Telasto.

The release coating 16 is formed from an acrylated silicone matrix with added silicone oil. The acrylated silicone matrix is formed of RC71 1 , photocompound 750, RC709 and RC902 all from Th. Goldschmidt. The silicone oil additive is

DMS-T35 from ABCR GmbH or 2000 Fluid (various viscosities) from Dow

Corning. Alternative components not marked with an asterix are also shown in

Table 2.

The results to various tests are shown in Table 3 where the components are those shown in Table 2. The precise composition of the various tape constructions and various compositions of the release coating 1 6 of the tested materials are shown in Table 3a, where d and c2 indicate comparative examples 1 and 2, respectively. Comparative Example 1 is a control example with no free silicone oil additive in the release coating. Comparative Example

2, is a similar composition except for the introduction of a low viscosity/low molecular weight PDMS liquid (DMS-T07 from ABCR GmbH) as an additive to the release coating. Examples 1 to 3 all include a free silicone oil additive with a molecular weight of about 6000 and viscosity of 100 (DMS-T21 from ABCR

GmbH) as the silicone oil additive in the release coating with the quantity of silicone oil additive varying in the three examples as shown in Table 3a.

Examples 4 to 6 all include a free silicone oil additive with a molecular weight of about 50000 and viscosity of 5000 (DMS-T35 from ABCR GmbH) as the silicone oil additive in the release coating with the quantity of silicone oil additive varying in the three examples as shown in Table 3a. Examples 7 to 9 all include a free silicone oil additive with a molecular weight of about 28000 and a viscosity of about 1000 (200 fluid, 1000 from Dow Corning Corporation).

Examples 10 to 12 all include a free silicone oil additive with a molecular weight of about 35000 and a viscosity of about 2000 (200 fluid, 2000 from Dow

Corning Corporation). Examples 1 3 and 14 each include a free silicone oil additive with a molecular weight of about 50,000 and a viscosity about 5000 (200 fluid, 5000 from Dow Corning Corporation). Examples 1 5 and 16 all include a free silicone oil additive with a molecular weight of about 68,000 and a viscosity about 12,500 (200 fluid, 12,500 from Dow Corning Corporation). Examples 17 to 19 all include a free silicone oil additive with a molecular weight of about 92,000 and a viscosity about 30,000 (200 fluid, 30,000 from Dow Corning Corporation). Examples 20 and 21 all include a free silicone oild additive with a molecular weight of about 120,000 and a viscosity about 60,000 (200 fluid, 60,000 from Dow Corning Corporation).

As will be clear from Table 3, the silicone oil additives of the present invention substantially reduce the adhesive properties of the adhesive layer 22 compared to the adhesive being brought into contact with a release coating not containing an additive (comparative example 1 ).

Low molecular weight and low viscosity silicone oils do not have a significant effect on the adhesive properties of the adhesive layer 22 as can be seen from comparative example 2 even in amounts up to 20 parts by weight. Without being bound by theory, the inventors believe that this is due to the low viscosity compounds having migrated too far through the adhesive. Whereas the medium viscosity compounds are not believed to penetrate in to the adhesive layer as readily. The results indicate that increases in molecular weight of viscosity of the free silicone oil decrease the final tack and peel adhesion. Increase in concentration of the free silicone oil decreases final tack and peel adhesion.

The amount of silicone oil additive in the release coating will normally be 1 parts to 20 parts by weight of the total of the release coating. Preferably between 3 parts and 8 parts.

The release coating, including the silicone oil additive, will normally be coated on the substrate with a weight of between about 0.1 g/m¹' and about 5.0g/m . Preferably the coating coat weight will be between about 0.5g/m² and about 2.0g/m . However as the weight of the additive increases the required amount required in the release coating will decrease. If any of the additive is consumed by the curing of the release coating then sufficient additive must be added to leave free additive a as required in the cured composition.

Example 22

Example 22 shows a brief aging profile of a tape made according to the present invention. Table 4 gives details of the construction and performance of the tape construction. The construction is generally the same as examples 1 to 21 , using the same adhesives, release coating, etc. The adhesive coat weight was 30g/m . The release coating weight 1 .2 g/m" containing 6 parts by weight of the silicone oil additive. The silicone oil additive in example 22 is a PDMS oil available under the trade name DMS-T35 from ABCR GmbH with a molecular

weight (Mr) of 49350.

As will be apparent from Table 4, the compositions according to the present invention are stable with time and temperature.

The data given in Table 4 and Fig. 6 shows that in the illustrated adhesive system there are several key transition points. At a molecular weight (Mr) of approximately 2000 leads to tack lowering to about 85% of the control value. The lowering of tack to 85% is considered to be illustrative of where a usable effect has been achieved though the molecular weight of additive which achieves this will depend ion the precise additive though currently it is believed that the additive would have a molecular weight of greater than 1000. It is also noted that a most significant reduction in tack to below 60 % of the control value is illustrated between the molecular weights of 6000 and 9500. The effects seem stable with time and temperature.

These effects show that the invention can be used to control the level of tack of an adhesive which has been in contact with a release coating having an additive of the present invention.

In Table 4, the following shorthand has been adopted:

Ageing: e.g. 1 month 50 °C means: sample roll stored during 1 month in an air circulated oven at temperature of 50°C. Afterwards the roll has been conditioned during 24 hours at 23°C and relative humidity of 50%, prior to execute the tests at 23 °C and relative humidity of 50%.

Finat tack on glass: relates to the standard adhesion test according PSTC-5, executed on floated glass.

90° Tape release: is the force needed to remove the fastening tape (20-22) from the release substrate 10, in the area where the substrate 10 is covered with release coating 16, at a speed of 10 m/min. The test gives an indication for the force needed to open a diaper tab prior to use.

Hinge force: is the force needed to separate the fastening substrate 20 from the release substrate 10, in the hinge area 26 where both carriers are bonded with fastening adhesive 22. The test is executed at 300 mm/min. The test gives information of functionality in end use; if the value is too low, separation of the two tapes in end use can occur.

90° peel adhesion on non release coated BOPP film: the fastening substrate 20 as coated is applied on a non-release coated BOPP film with pressure of 1 lbs.

Afterwards the force needed to remove this tape, under an angle of 90° and speed of 300 mm/min is measured. As this non-release coated BOPP film is the diaper tape landing zone, this test gives an indication of the functionality in end use: a too low value will give pop opens during end use, a too value will make it impossible to open the diaper tab without destroying the diaper. Table 2

Table 3

Table 3a

Table 4

Table 4 con't

Generally, the invention relates to release coatings used to provide certain adhesive qualities for adhesives adhering thereto. The release coating includes an additive, such as a polydimethyl siloxane, or derivative thereof. The additive alters the adhesion of an adhesive to other substrates after having been brought into contact with the release coating.

Claims

Claims:

1 . A release coating composition comprising a release coating composition curable to form a release coating matrix and a free silicone oil additive having a molecular weight of at least 1000 and/or a viscosity of at least 10 cSt.

2. A release coating according to claim 1 , wherein the free silicone oil is a siloxane of the general formula:

(X or R)-SiR₂-0-(Si(R₂)-0)_a-0-(Si(RX)-0)_b-(Si(RY))-0)_c -SiR₂-(X or R) where X is selected from the group consisting of: alkyl; alkenyl; hydrogen; hydroxide; amino; epoxy; carbonyl; and halide; and where Y represents a polysiloxane branching of the main polysiloxane chain, which may contain organic functionality like X located on - or at the end of this side chain; and where a, b and c are independent integers, c is greater than or equal to 0, b is greater than or equal to 0 and a is greater than 0.

3. A release coating according to claim 1 or claim 2, wherein the silicone oil additive will not participate in the curing of the release coating component.

4. A release coating according to any one of the preceding claims, wherein the release coating comprises a curable silicone or carbamide.

5. A release coating according to claim 4, wherein the release coating is formed in a solventless curing system.

6. A release coating according to any one of the preceding claims, wherein the free silicone oil additive has a molecular weight of greater than 5000.

7. A release coating according to any one of the preceding claims, wherein the free silicone oil additive is a liquid and/or has a molecular weight of less than 1 ,000,000.

8. A release coating according to any one of the preceding claims, wherein the free silicone oil additive comprises at least 3 parts by weight of the cured release coating composition

9. A release coating according to any one of the preceding claims, wherein the free silicone oil additive comprises 6 to 8 parts by weight of the total of the release coating.

10. An adhesive construction comprising a generally planar release substrate and a generally planar fastening substrate, where a first surface of the release substrate is juxtaposed to a first surface of the fastening substrate with a adhesive sandwiched therebetween, wherein a release portion of the first surface of the release substrate is coated with a release coating so that the opposed portion of the fastening substrate with the associated adhesive is peelable from the release portion, the release coating composition including an additive which alters the tackiness of the adhesive.

1 1 . An adhesive construction according to claim 10, wherein comprises the release coating composition according to any one of claims 1 to 9.

12. An adhesive construction according to claim 10 or 1 1 , wherein the release substrate comprises a release tape and the fastening substrate comprises a fastening tape.

13. An adhesive construction according to claim 12, wherein the release tape and/or the fastening tape is formed from polypropylene, polyethylene or other suitable plastics material.

14. An adhesive construction according to any one of claims 10 to 16, wherein the release tape and/or the fastening tape is formed from films selected from the group consisting of cast polypropylene mono and bi-orientated polypropylene, polyethylene, PVC and polyester film.

15. An adhesive construction according to any one of claims 12 to 14, wherein the release tape substrate is also coated on its other side with an adhesive.

16. An adhesive construction according to any one of claims 12 to 1 5, wherein the fastening tape substrate is not coated on its opposite side with an adhesive.

17. An adhesive construction according to any one of claims 10 to 16, wherein the construction is a multi-layered tape.

18. An adhesive construction according to claim 10 or claim 1 1 , wherein the release substrate comprises a backing layer and the fastening substrate comprises a face stock.

19. An adhesive construction according to claim 18, wherein the backing layer and/or the face stock is formed from paper or a paper-based material.

20. An adhesive construction according to claim 18 or claim 19, wherein the whole of the backing layer is covered with the release coating.

21 . An adhesive construction according to any one of claims 18 to 20, wherein the construction comprises a label construction.

22. An adhesive construction according to any one of claims 10 to 21 , wherein the release substrate is not the same as the fastening substrate.

23. An adhesive construction according to any one of claims 10 to 22, wherein the adhesive is a pressure sensitive adhesive.

24. An adhesive composition according to claim 23, wherein the pressure sensitive adhesive composition contain an adhesive polymer such as a natural, reclaimed or styrene-butadiene rubber, styrene butadiene or styrene isoprene block copolymers, polyisobutylene, poly (vinylether) or poly (acrylic) ester as a major constituent.

25. A method for producing a release coating, including the step of coating a release substrate with a release coating composition where the release coating composition includes an additive which effects the tack of adhesives brought into contact with the release coating composition.

26. A method according to claim 15, wherein the release coating composition is applied only selected portions of the release substrate.

27. A method for producing a multilayered article including the method according to claim 25 or claim 26, where an adhesive layer overlies the release substrate including the area covered with the release coating composition.

28. A method according to claim 27, wherein the adhesive is sandwiched between the release substrate and a fastening substrate.

29. A method according to any one of claims 25 to 28, further including the step of curing the release coating composition when on the release substrate.

30. A method according to claim 29 wherein the coating is cured by actinic radiation, by temperature, or other combination thereof.

31 . A method according to any one of claims 25 to 30, wherein the release coating composition comprises a release coating composition according to any one of claims 1 to 9.

32. A method according to any one of claims 25 to 31 used to form the constructions of any one of claims 10 to 24.

33. A release coating as hereinbefore described with reference to, and/or as illustrated by, the accompanying drawings.

34. An adhesive construction as hereinbefore described with reference to, and/or as illustrated by, the accompanying drawings.

35. A method for producing a release coating or incorporating the production of a release coating as hereinbefore described with reference to, and/or as illustrated by, the accompanying drawings.