PRESSURE SENSITIVE ADHESIVES

This invention relates to pressure sensitive adhesives (PSA) based on aqueous emulsions and processes for preparation of the adhesives. The pressure sensitive adhesives of the invention have enhanced resistance to water-whitening preferably with improved peel and shear balance suitable for adhesion to a wide variety of substrates including those with low surface energy.

There is an increasing desired to provide no label look labels to improve eye appear to the consumer. This requires a highly transparent label adhesive laminate (i.e. facestock coated with PSA) so when the label is attached to the product, information appears to be directly printed thereon for maximum aesthetic impact. There is also a desire to use water borne rather than solvent based adhesives for environmental and other reasons. However conventional waterborne adhesives exhibit very poor water whitening resistance as the dried adhesive film quickly turns white when exposed to water. In many applications labels are exposed to water (e.g. labelled beverage containers may be cooled in an ice bath) where conventional aqueous PSAs would whiten and destroy the desired no label look.

A further problem exists as PSAs suitable for high energy surfaces (such as stainless steel or glass) are not necessarily suitable for use on low energy surfaces such as polymers (e.g. polyethylene or polypropylene). To obtain PSA with the suitable adhesive properties (such as a good balance between peel, adhesion and shear) on a low energy surface requires modification of a conventional PSA formulated for a high energy surface. This is even more challenging for water whitening PSAs as it has been found the modifications (for example adjusting the monomer composition) that may be necessary to enhance adhesive performance of a PSA on low surface energy substrates may decrease or eliminate the desired level of water whitening resistance.

Various adhesives with water whitening resistant properties are described are described in the prior art.

The applicant's patent applications: WO 03/006517, WO 03/006518, WO 04/029171 , WO 04/029172 and WO 05/044880 disclose PSAs with good water whitening resistance.

US 2005/0176876 (Avery) describes an acrylic PSA composition where use of a combination of two specific monomers i) a trifluoroalkyl (meth)acrylate and ii) an alkylimidazolidone (meth)acrylate is stated to enhance water whitening of this PSA.

WO 00/61670 (Ashland) (= EP 1 198502-A, US 2004-0076785 and US 6359092) describes a water whitening resistant PSA obtained from a monomer composition consisting essentially of a C>=4 alkyl acrylate, an ethylenically unsaturated acid or anhydride and stryene. This reference teaches that one should not use any additional monomers. The reference also teaches that use of a redox polymerisation initiator is an essential element to prepare these PSAs and that it is required for the dispersed phase in the PSA emulsion to have an average particle size of 100 nm or less.

WO 01/85867 (Ashland) (= EP 1240267-A, US 2004 0076785 and US 6359092) describes water whitening resistant PSAs obtaining using as the only emulisfier a polymeric surfactant of the structure:

where Ri is C ₆ -i ₈ alkyl, C ₆ -i ₈ alkenyl, or C _6- i ₈ aralkyl, R ₂ is H or R ₁ , R ₃ is H or propenyl; A is an C _2-4 alkylene, n is an integer from 1 to 200, and M is an alkali metal, an ammonium ion, or an alkanolamine cation. The preferred and exemplied emulsifier is

(Hitenol BC 10). This reference does not consider the problem of providing improved adhesive properties on low energy surfaces.

None of these references provide a satisfactory solution to the problem of enhancing the adhesive properties on low energy surfaces, whilst maintaining water whitening resistance.

It is therefore an object of the present invention to solve some or all of the problems with the prior art adhesives. The present invention relates to a composition of and process for making a waterborne adhesive which combines acceptable water whitening resistance with good adhesion properties on most surfaces including low energy surfaces.

In general there are few aqueous PSA which have acceptable resistance to water whitening and it was believed there are limitations in the way such PSAs can be

modified without reducing or eliminating the desired water whitening properties. Surprisingly the applicant has found an adhesive formulation which has both acceptable water whitening resistance and also good adhesive properties on low energy surfaces (and optionally also high energy surfaces)

Therefore broadly in accordance with the present invention there is provided an aqueous dispersion suitable for preparing pressure sensitive adhesive (PSA) having acceptable, optionally enhanced, resistance to water-whitening and acceptable, optionally enhanced, adhesive properties to substrates of low surface energy, where the dispersion:

(a) comprises a monomer composition comprising:

(i) at least one hydrophobic monomer (Component I), (ii) at least one hydrophilic monomer (Component II) (iii) at least one partially hydrophilic monomer (Component III) (iv) at least one a monomer of Formula 1 (Component IV)

Formula 1 where

Y denotes an electronegative group,

R ⁰ is H, OH or an optionally hydroxy subsitituted Ci_iohydrocarbo R ¹ is H or a d.-iohydrocarbo;

R ² is a Ci.iohydrocarbo group substituted by at least one activated unsaturated moiety; and

A represents a divalent organo moiety attached to both the HN and Y moieties, x is an integer from 1 to 4; where the A, NH, C=O and Y moieties together represent a ring having from 4 to 8 ring atoms, and R ¹ and R ² are attached to any suitable point on the ring; (b) comprises at least one water-soluble or water-dispersible polymerizable surfactant (c) has an average particle size of from about 50 nm to about 300 nm; (d) has a pH of from about 5.5 to about 9.0. with the provisos that the dispersions of the invention are substantially free of trifluoroalkyl (meth)acrylate monomers; and

Formula 1 represents other than 1-ethenyl- pyrrolidone (i.e. when R ² is ethenyl attached to the ring nitrogen and together R ¹ , A and Y represent a n-propylene group then x is from 2 to 4).

Adhesive emulsions of the invention exhibit acceptable water whitening resistance combined with high shear and peel adhesion on low energy surfaces and are suitable for uses such as waterborne adhesives to fix clear labels onto a wide variety of substrates for a no label look.

Water whitening resistance

To test for water whitening resistance a test strip coated with a PSA is prepared conventionally (for example as described in the example section herein). The PSA strip is immersed in water at a specified temperature for 30 minutes and the appearance of the strip is then immediately assessed to determine its water whitening resistance. The assessment may be made visually by rating the test strips on a scale 0 (clear) to 5.0 (completely white / opaque). To assist the visual rating the test strip may be usefully compared against a series of photographs of standard strips pre-determined as having each rating. Alternatively the assessment may be measured by the increase of absorbance (as determined by UV/Visible spectroscopy) before and after immersion. If no temperature is specified herein the immersion was at ambient temperature (20 ⁰ C).

It is preferred that PSAs which are used in applications such as beverage labels are resistant to water whitening at higher temperatures (90°C) as the labelled containers are pasteurised at such temperatures. However for other applications (such as labelling of health and beauty products) pasteurisation is not required and thus PSA that exhibit water whitening resistance at lower temperatures are also useful.

The PSAs of the present invention exhibit acceptable, preferably enhanced, resistance to water-whitening at ambient temperature. More preferred PSAs of the invention exhibit acceptable, most preferably enhanced water resistance at 90°C (i.e. are also pasteurisation resistant).

As used herein these terms are defined as follows for a given temperature after 20 minutes immersion: 'Acceptable' water whitening resistance means a rating of 1.5 or lower on the visual scale and/or an increase of absorbance of less than 0.2.

'Enhanced' water whitening resistance means a visual rating of 0.5 or lower and/or an increase of absorbance of less than 0.05.

As a comparison conventional aqueous PSA formulations which are not resistant to water whitening typically have a visual rating of 5.0 after immersion at ambient temperature for only 10 minutes.

Adhesive properties on substrates of low surface energy

It is a preferred advantage of the invention that the adhesives may be applied to a wide range of substrates of high or of low surface energy. Prior art PSAs formulated for high energy substrates generally have poor performance on low energy substrates and thus different PSAs are often required with different substrates. The present invention has improved adhesive properties on low energy surfaces and in one embodiment it may also exhibit good adhesive properties on high energy surfaces. Thus PSA of the invention may have acceptable, preferably enhanced, water whitening resistance and also acceptable preferably enhanced adhesive properties on a wide variety of substrates. An alternative embodiment of the invention provides PSAs where the adhesive properties are optimized for low energy surfaces alone.

The adhesive properties desired when a PSA is applied to a particular substrate depend on the specific requirements of the end user. It is preferred that the desired adhesive properties for PSAs of the present invention (tested by the methods described herein) may be as follows. A PSA with acceptable adhesive performance may have a shear value of at least 20 hours and/or a peel value (after aging for 24 hours) of at least 0.5 pounds per inch. A PSA with enhanced adhesive performance may have a shear value of at least 50 hours and/or a peel value (after aging for 24 hours) of at least 1.0 pounds per inch.

Surface energy may be measured by standard methods as a critical surface tension in dynes per cm. The surface energy of common solid substrates as follows: polyethylene (PE) = 31 , poly vinyl chloride (PVC) = 39, polyethylene terephthalate (PET) = 43. aluminium = ~ 500; and copper = ~ 1000. Preferred low surface energy substrates on which the adhesives of the invention may preferably have acceptable, more preferably enhanced adhesive performance of those having a surface energy of no more than 100 dynes per cm, more preferably < 50 dynes / cm.

Monomer composition

Unless otherwise indicated (e.g. for amounts of aryl arylalkylene within Component I) all of the weight amounts described herein for the following monomers are given as weight percentages by the total weight of monomers (Components I, II, III & IV).

Component I

The hydrophobic monomer (Component I) may comprise, conveniently consist essentially of, at least one hydrophobic (meth)acrylate and/or arylalkylene monomer.

Preferably the hydrophobic (meth)acrylate comprises C> ₄ hydrocarbo (meth)acrylate(s) and conveniently the C> ₄ hydrocarbo moeity may be C _4-2 ohydrocarbyl, more conveniently C _4- i ₄ alkyl most conveniently C _4- ioalkyl, for example C _4-8 alkyl.

Suitable hydrophobic (meth)acrylate(s) are selected from: isooctyl acrylate, 4-methyl-2-pentyl acrylate, 2-methylbutyl acrylate, isoamyl acrylate, sec-butyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, isodecyl methacrylate, isononyl acrylate, isodecyl acrylate, and/or mixtures thereof, especially 2-ethylhexyl acrylate and/or n-butyl acrylate, for example 2-ethylhexyl acrylate .

Preferably the arylalkylene comprises (optionally hydrocarbo substituted) stryene and conveniently the optional hydrocarbo may be Ci.iohydrocarbyl, more conveniently Ci _-4 alkyl.

Suitable arylalkylene monomers are selected from: styrene, α-methyl styrene, vinyl toluene, t-butyl styrene, dimethyl styrene and/or mixtures thereof, especially styrene.

The arylalkylene monomer may be present in Component I (the total hydrophobic monomer) up to about 30%, preferably from about 1 % to about 20%, and more preferably from about 5% to about 15% by total weight of Component I.

The currently preferred Component I is a mixture of 2-ethylhexyl acrylate and/or n-butyl acrylate with styrene, more preferably a mixture of 2-ethylhexyl acrylate and stryene.

Component I may be present in a total amount from about 70% to about 90%, preferably from about 75% to about 85% by weight.

Component Il

Suitable hydrophilic monomers of Component Il are those that are copolymerizable with the hydrophobic monomer(s) (Component I) and are water soluble.

Preferred hydrophilic monomers comprise, conveniently consist essentially of, at least one ethylenically unsaturated carboxylic acid. More preferred acids have one ethylenic group and one or two carboxy groups. Most preferably the acid(s) are selected from the group consisting of: acrylic acid (and oligomers thereof), beta carboxy ethyl acrylate, citraconic acid, crotonic acid, fumaric acid, itaconic acid, maleic acid, methacrylic acid and mixtures thereof; for example acrylic acid, methacrylic acid and mixtures thereof.

Component Il may be present in a total amount of at least about 1 %, preferably from about 2% to about 10%, more preferably from about 3% to about 9%, most preferably from about 4% to about 8% by weight.

Component III

The partially hydrophilic monomers of Component III may also be referred to as partially water soluble monomers.

Preferred partially hydrophilic monomers comprise, conveniently consist essentially of, at least one (meth)acrylate. More preferred partially hydrophilic monomers are selected from the group consisting of: methyl acrylate, methyl methacrylate, ethyl acrylate and mixtures thereof; most preferably methyl acrylate, methyl methacrylate, and mixtures thereof, for example methyl acrylate.

Component III may be present in a total amount of at least about 5%, preferably from about 5% to about 20%, more preferably from about 5% to about 18%, most preferably from about 10% to about 16% by weight.

Component IV

Component IV comprises, conveniently consists essentially of, at least one monomer of Formula 1 above.

Activated unsaturated moiety

In Formula 1 , R ² comprises at least one "activated unsaturated moiety", a term used to denote a species comprising at least one unsaturated carbon to carbon double bond in chemical proximity to at least one activating moiety. Preferably the activating moiety comprises any group which activates an ethylenically unsaturated double bond for addition thereon by a suitable electrophillic group. Conveniently the activating moiety comprises oxy, thio, (optionally organo substituted)amino, thiocarbonyl and/or carbonyl groups (the latter two groups optionally substituted by thio, oxy or (optionally organo

substituted) amino). More convenient activating moieties are (thio)ether, (thio)ester and/or (thio)amide moiet(ies). Most convenient "activated unsaturated moieties" comprise an "unsaturated ester moiety" which denotes an organo species comprising one or more "hydrocarbylidenyl(thio)carbonyl(thio)oxy" and/or one or more "hydrocarbylidenyl(thio)- carbonyl(organo)amino" groups and/or analogous and/or derived moieties for example moieties comprising (meth)acrylate functionalities and/or derivatives thereof. "Unsaturated ester moieties" may optionally comprise optionally substituted generic α,β-unsatu rated acids, esters and/or other derivatives thereof including thio derivatives and analogs thereof.

Preferred activated unsaturated moieties in Formula 1 are those represented by a radical of Formula 2.

Formula 2 where n is 0 or 1 , X ¹ is oxy or, thio; X ² is oxy, thio or NR ⁷ (where R ⁷ represents H or optionally substituted organo), R ³ , R ⁴ R ⁵ and R ⁶ each independently represent a bond to another moiety in Formula 1 , H, optional substituent and/or optionally substituted organo groups, where optionally any of R ³ , R ⁴ R ⁵ and R ⁶ may be linked to form a ring; where at least one of R ³ , R ⁴ R ⁵ and R ⁶ is a bond; and all suitable isomers thereof, combinations thereof on the same species and/or mixtures thereof.

The terms "activated unsaturated moiety"; "unsaturated ester moiety" and/or Formula 2 herein represents part of a monomer of Formula 1 herein and as used herein these terms denote a radical moiety which depending where the moiety is located in Formula 1 may be monovalent or multivalent (e.g. divalent). Thus in Formula 2 it will be appreciated that at least one of R ³ , R ⁴ R ⁵ and R ⁶ denote a single covalent bond i.e. denote where Formula 2 is attached to the remainder of the monomer of Formula 1.

More preferred moieties of Formula 2 (including isomers and mixtures thereof) are those where n is 1 ; X ¹ is O; X ² is O, S or NR ⁷ .

R ³ , R ⁴ R ⁵ and R ⁶ are independently selected from: a bond, H, optional substituents and optionally substituted Ci.iohydrocarbo, optionally R ⁵ and R ⁶ may be linked to form (together with the moieties to which they are attached) a ring; and where present R ⁷ is selected from H and optionally substituted Ci.iohydrocarbo.

Most preferably n is 1 , X ¹ is O; X ² is O or S and R ³ , R ⁴ R ⁵ and R ⁶ are independently a bond, H, hydroxy and/or optionally substituted Ci tøydrocarbyl.

For example n is 1 , X ¹ and X ² are both O; and R ³ , R ⁴ R ⁵ and R ⁶ are independently a bond, H, OH, and/or or optionally R ⁵ and R ⁶ may together form a divalent Co- ₄ alkylenecarbonylC ₀ - ₄ alkylene moiety so Formula 2 represents a cyclic anhydride (e.g. when R ⁵ and R ⁶ together are carbonyl then Formula 2 represents a maleic anhydride or derivative thereof).

For moieties of Formula 2 where n is 1 and X ¹ and X ² are both O then when one of (R ³ and R ⁴ ) is H and also R ³ is H, Formula 2 represents an acrylate moiety, which includes acrylates (when both R ³ and R ⁴ are H) and derivatives thereof (when either R ³ and R ⁴ is not H). Similarly when one of (R ³ and R ⁴ ) is H and also R ⁵ is CH ₃ , Formula 2 represents an methacrylate moiety, which includes methacrylates (when both R ³ and R ⁴ are H) and derivatives thereof (when either R ³ and R ⁴ is not H). Acrylate and/or methacrylate moieties of Formula 2 are particularly preferred.

Conveniently moieties of Formula 2 are those where n is 1 ; X ¹ and X ² are both O; R ³ and R ⁴ are independently a bond, H, methyl or OH, and R ⁵ is H or CH ₃ ; R ⁶ is H or R ⁵ and R ⁶ together are a divalent C=O group.

More conveniently moieties of Formula 2 are those where n is 1 ; X ¹ and X ² are both O; R R ³³ iiss OOHH,, RR ⁴⁴ iiss CCHH ₃₃ ,, aanndd RR ⁵⁵ iiss HH aanndd RR ⁶⁶ iiss aa bond and/or tautomer(s) thereof (for example of an acetoacetoxy functional species).

Most convenient unsaturated ester moieties are selected from: -OCO-CH=CH ₂ ; -OCO-C(CHs)=CH ₂ ; acetoacetoxy, -OCOCH=C(CH ₃ )(OH) and all suitable tautomer(s) thereof.

It will be appreciated that any suitable moieties represented by Formula 2 could be used in the context of this invention such as other reactive moieties.

Formula 1

The ring moiet(ies) of Formula 1 are each attached to R ² and in Formula 1 when x is 2, 3 or 4 then R ² is multi-valent (depending on the value of x). If x is not 1 R ¹ and Y may respectively denote the same or different moieties in each ring, preferably the same

respective moieties in each ring. R ¹ and R ² may be attached at any suitable position on the ring.

Preferred monomers of Formula 1 comprise, conveniently consist essentially of, those where:

A represents a optional substituted divalent Ci _-5 hydrocarbylene; and

Y is divalent NR (where R' is H, OH, optionally hydroxy subsitituted Ci_iohydrocarbo or R ² ) or divalent O,

More preferred monomers of Formula 1 comprise those where: x is 1 or 2

Y is NR ² (i;e. where Formula 1 is attached to R ² via a ring nitrogen) A represents a divalent Ci _-3 hydrocarbylene;

R ⁰ is H, R ¹ is a C-i-iohydrocarbo; and

R ² comprises a (meth)acryloxyhydrocarbo group or derivative thereof (e.g. maleic anhydride); and

Most preferred monomers of Formula 1 comprise those where: x is 1 , or 2 and the (optionally repeating) unit in Formula is represented by Formula 3

where the asterisk denotes the point of attachment of Formula 3 to R ² (which may be at any suitable point on the ring preferably via a ring nitrogen); and R ¹ is H or Ci _-8 hydrocarbyl R ² comprises a (methOacryloxyd-iohydrocarbo group.

More preferred monomers of Formula 1 comprise:

where R ¹ is H or Ci _-6 alkyl and L is a suitable divalent organo linking group (such as Ci-i ₀ hydrocarbylene, for example Ci _-6 alkylene).

Further suitable uredo monomers of Formula 1 are described in "Novel wet adhesion monomers for use in latex paints" Singh et al, Progress in Organic Coatings, 34 (1998),

214-219, (see especially sections 2.2 & 2.3) and EP 0629672 (National Starch) both of which are hereby incorporated by reference.

Examples of monomers of Formula 1 are selected from:

(where n is 1 to 4),

(available commercially from Cytec under the trade mark

Sipomer ^® WAM II) and suitable mixtures thereof.

Conveniently Component IV may be used as a substantially pure compound (or mixture of compounds) of Formula 1 or may be dissolved in a suitable solvent such as a suitable (meth)acrylate or acrylic derivative for example methyl methacrylate. Optionally such solutions may comprise from about 50% to about 75% by weight of Component IV.

Component IV may be present in a total amount from at least about 0.1 %, preferably from about 0.1 % to about 2.0%, more preferably from about 0.2% to about 1.0%, most preferably from about 0.3% to about 0.6% by weight.

Polymerisible surfactant

Water-soluble or water-dispersible polymerizable surfactants that can be employed according to the invention include those polymerizable surfactants disclosed in US 5928783, US 6239240, WO 03/006517 and WO 03/006518, which are incorporated herein by reference in their entirety.

Preferably, the polymerizable surfactants of the invention contain a hydrophilic portion which may comprise an (optionally terminal) allyl amine moiety, such as a sulfonate allyl amine moiety, a sulfate allyl amine moiety and/or a phosphate allyl amine moiety, and a hydrophobic portion which comprise a moiety selected from -R', or a group having the formula RO-(CH ₂ CH ₂ O) _n -; where R' denotes Ci _-20 hydrocarbyl, preferably

Ci_ ₂ oalkyl or an Ci _-2 oalkylphenyl, more preferably Ci _O -i ₈ alkyl or Ci _O -i ₈ alkylphenyl;and n is an integer from 2 to 100, preferably from 2 to 50; most preferably from 5 to 20. The hydrophilic portion and the hydrophobic portion may be connected by means of a covalent or ionic bond, preferably a covalent bond. Combinations of such polymerizable surfactants can be used in preparing the polymers of the invention.

Suitable water-soluble or water-dispersible polymerizable surfactants may comprise but are not limited to, the following embodiments by way of example.

In one embodiment the polymerizable surfactant may comprise a compound of Formula 4

Formula 4 where

R ⁹ (preferably attached on the ring para to the sulpho group) is a hydrocarbo, preferably Ci _-2 ohydrocarbyl, most preferably Cio-isalkyl for example docdecyl;

R ¹⁰ , R ¹¹ and R ¹² independently represent H or optionally substituted Ci- ₆ alkyl, preferably H or optionally hydroxy substituted d- ₆ alkyl, more preferably at least one of

R ¹⁰ , R ¹¹ and R ¹² is H the others being optionally hydroxy substituted Cr ₄ alkyl, most preferably all are H.

Conveniently compounds of Formula 4 may comprise

In another embodiment the polymerizable surfactant may comprises a compound of Formula 5

Formula 5 where

R ¹³ is Ci_ ₄ alkylene, preferably C ₂ - ₄ alkylene, most preferably ethylene or propylene R ¹⁴ , R ¹⁵ and R ¹⁶ independently represent H or Ci _-30 hydrocarbo, preferably H or C6- ₂ ohydrocarbyl where at least one of R ¹⁴ , R ¹⁵ and R ¹⁶ are H, more preferably R ¹⁴ is

C _6- i ₈ alkyl, C ₆ -i ₈ alkenyl, or C _6- i ₈ aralkyl, R ¹⁵ is H or more preferred R ¹⁴ , and R ¹⁶ is H or propenyl; n is an integer from 1 to 200, preferably from 2 to 50, more preferably from 5 to 30, for example 15 to 25, e.g. 20; and M is any suitable cation such as an alkali metal cation, optionally alkyl substituted ammonium or an alkanolamine cation.

Conveniently compounds of Formula 5 may comprise

where the radical CgH ₁₉ represents a mixture of isomers, and such compounds are those available commerically from Dai-lchi Kogyo Seiyaku Co., Ltd. (Tokyo, Japan) under the trade marks Hitenol® BC10 (when n is 10) or Hitenol® BC20 (when n is 20).

In yet another embodiment the polymerizable surfactant may comprises a compound of Formula 6

.1 177 i <» , F I . RK ²¹

R

O -K Όc - O-Q ^" N _N

R ²⁰ Formula 6 where

R ¹⁷ is Ci _-2 ohydrocarbyl, preferably Cio-isalkyl; R ¹⁸ is divalent C-^alkylene, preferably propylene or ethylene;

Q ^" is an acid anionic substituent such as -SO ₃ ^" or PO ₄ ^" m is an integer from 2 to 100, preferably 2 to 15, and

R ¹⁹ , R ²⁰ and R ²¹ are independently as given for respectively R ¹⁰ , R ¹¹ and R ¹² above, preferably are all H.

Examples of a polymerizable surfactant of Formula 6 are allyl amine salts of laureth sulfate or nonylphenol ethoxylate (9 moles EO) phosphate esters and a compound of formula

H ₃ N

and when R ¹⁷ is lauryl such compounds are available commercially from Stepan Company under the trade mark Polystep® NMS.

In a still yet another embodiment the polymerizable surfactant may comprises a compound of Formula 7

R ²² -SO ₃ ^{" +} NR ²³ (R ²⁴ )(R ²⁵ )-CH ₂ -CH=CH ₂ Formula 7 where R ²² is C6- ₂ ohydrocarbyl, preferably Cio-isalkyl; R R ²²³³ ,, RR ²²⁴⁴ aanndd RR ²²⁵⁵ aarree independently as given for respectively R ¹⁰ , R ¹¹ and R ¹² above, preferably are all H.

In a still yet further embodiment the polymerizable surfactant may comprises a compound of Formula 8

R ^2β ^ '"

Formula 8 where

R ²⁶ is a C _8- 3ohydrocarbo, preferably C _8- i ₄ hydrocarbyl, preferably Ci _O -i ₂ alkyl

R ²⁷ is H or methyl, preferably H

R ²⁸ is an unsubstituted or substituted divalent C ₂ - ₄ alkylene group, preferably propylene or ethylene; p is 0 or an integer of 1 to about 200, preferably 2 to about 100, more preferably 2 to about 30; for example 5 to 10; and

Z is an alkali metal, an ammonium ion, or an alkanolamine residue.

Examples of alkanolamine residues include monoethanolamine, triethanolamine, and the like.

Suitable polyoxyalkylene-i-(allyloxymethyl) alkyl ether sulfate salts of Formula 8 include those disclosed in JP 2596441 (Dai-lchi Kogyo Seiyaku Co., Ltd.) and may be preapred as described therein. Suitable compounds of Formula 8 are available from

Dai-lchi under the trademark Hitenol® KH.

Polvoxyalkylene groups

In respective Formulae 5, 6 and 8, R ¹³ , R ¹⁸ and R ²⁸ represent part of a polyoxyalkylene repeat unit for example suitable unsubstituted or substituted alkylene groups such as ethylene, propylene, butylene, and isobutylene. The polyoxyalkylene

moiety comprising respectively, n; m or p repeat units can be a homo-, block or random polymer, or any suitable mixtures thereof.

The total amount of water-soluble or water-dispersible polymerizable surfactant that may present in the dispersion is at least about 0.1 %, preferably from about 0.1 % to about 5%, preferably about 0.5 to about 2 %, by weight of the total amount of Components I, Il , III and IV.

A most preferred PSA composition comprises (advantageously consists of) of the following monomers: 2-ethylhexyl acrylate; styrene; ethyl acrylate; acrylic acid, beta-carboxy ethyl acrylate; 2-methacryloxyethyl-2-imidazolidone and

Particle size

The applicant has suprisingly found that the PSAs of the invention can be made with a larger particle size than previously thought necessary for water whitening resistance and the PSA still retains acceptable resistance to water whitening. There are process advantages in using a larger particle size (e.g. reduced viscosity) so in a preferred embodiment of the invention the particle size of the PSA is more than 100 nm, conveniently from about 100 nm to about 300 nm, more conveniently from about 200 nm to about 300 nm. The particle sizes herein are number average which may be measured by any suitable method such as light scattering.

βH

Preferred emulsions of the invention have a pH of from about 6.0 to about 8.5.

Process

Broadly in accordance with another aspect of the present invention there is provided a process for preparing an aqueous dispersion suitable for preparing pressure sensitive adhesive (PSA) having enhanced resistance to water-whitening and good adhesive properties to substrates of low surface energy, the process comprising the steps of: (a) copolymerising a monomer composition comprising: (i) at least one hydrophobic monomer (Component I),

(ii) at least one hydrophilic monomer (Component II) (iii) at least one partially hydrophilic monomer (Component III) (iv) at least one a monomer of Formula 1 (Component IV)

Formula 1 where

Y denotes an electronegative group,

R ⁰ is H, OH or an optionally hydroxy subsitituted d.-iohydrocarbo, R ¹ is H or a C-i.-iohydrocarbo;

R ² is a Ci.iohydrocarbo group substituted by at least one activated unsaturated moiety; and

A represents a divalent organo moiety attached to both the HN and Y moieties, x is an integer from 1 to 4; where the A, NH, C=O and Y moieties together represent a ring having from 4 to 8 ring atoms, and R ¹ and R ² are attached to any point on the ring; in the presence of at least one water-soluble or water-dispersible polymerizable surfactant to form a acrylic emulsion having an average particle size of from about 50 nm to about 300 nm;

(b) neutralising the emuslion so that the pH is from about 5.5 to about 9.0. with the provisio that the monomer composition is substantially free of trifluoroalkyl (meth)acrylate monomers.

Preferably step (a) is performed in the absence of a redox initiator, more preferably step (a) is performed in the presence of a thermal initator. Most preferably step (a) is a radical co-polymerisation.

Suitable thermal initiators include potassium persulfate.

Further detail and additional optional ingredients that may be used in the process of he present invention are known to those skilled in the art, for example step (a) may be performed in the presence of a chain transfer agent such as n-dodecyl mercaptane. Suitable methods and optional ingredients are described in the examples herein and also in the applicant's patent applications WO 03/006517, WO 03/006518, WO 04/029171 , WO 04/029172 and WO 05/044880 herby incorporated by reference.

Many other variations embodiments of the invention will be apparent to those skilled in the art and such variations are contemplated within the broad scope of the present invention.

Further aspects of the invention and preferred features thereof are given in the claims herein.

Unless the context clearly indicates otherwise, as used herein plural forms of the terms herein are to be construed as including the singular form and vice versa.

The term "comprising" as used herein will be understood to mean that the list following is non exhaustive and may or may not include any other additional suitable items, for example one or more further feature(s), component(s), ingredient(s) and/or substituent(s) as appropriate.

The terms 'effective', 'acceptable' 'active' and/or 'suitable' (for example with reference to any process, use, method, application, preparation, product, material, formulation, compound, monomer, oligomer, polymer precursor, and/or polymers of the present invention and/or described herein as appropriate) will be understood to refer to those features of the invention which if used in the correct manner provide the required properties to that which they are added and/or incorporated to be of utility as described herein. Such utility may be direct for example where a material has the required properties for the aforementioned uses and/or indirect for example where a material has use as a synthetic intermediate and/or diagnostic tool in preparing other materials of direct utility. As used herein these terms also denote that a functional group is compatible with producing effective, acceptable, active and/or suitable end products.

Preferred utility of the present invention comprises uses as an adhesive, preferably a pressure sensitive adhesive. It is desired that adhesives of the invention have acceptable resistance to water whitening and have good adhesive properties on substrates of low surface energy preferably on a wide variety of substrates.

The terms 'optional substituent' and/or 'optionally substituted' as used herein (unless followed by a list of other substituents) signifies the one or more of following groups (or substitution by these groups): carboxy, sulpho, formyl, hydroxy, amino, imino, nitrilo, mercapto, cyano, nitro, methyl, methoxy and/or combinations thereof. These optional groups include all chemically possible combinations in the same moiety of a plurality (preferably two) of the aforementioned groups (e.g. amino and sulphonyl if directly attached to each other represent a sulphamoyl group). Preferred optional substituents

comprise: carboxy, sulpho, hydroxy, amino, mercapto, cyano, methyl, halo, trihalomethyl and/or methoxy.

The synonymous terms Organic substituent' and "organic group" as used herein (also abbreviated herein to "organo") denote any univalent or multivalent moiety (optionally attached to one or more other moieties) which comprises one or more carbon atoms and optionally one or more other heteroatoms. Organic groups may comprise organoheteryl groups (also known as organoelement groups) which comprise univalent groups containing carbon, which are thus organic, but which have their free valence at an atom other than carbon (for example organothio groups). Organic groups may alternatively or additionally comprise organyl groups which comprise any organic substituent group, regardless of functional type, having one free valence at a carbon atom. Organic groups may also comprise heterocyclyl groups which comprise univalent groups formed by removing a hydrogen atom from any ring atom of a heterocyclic compound: (a cyclic compound having as ring members atoms of at least two different elements, in this case one being carbon). Preferably the non carbon atoms in an organic group may be selected from: hydrogen, halo, phosphorus, nitrogen, oxygen, silicon and/or sulphur, more preferably from hydrogen, nitrogen, oxygen, phosphorus and/or sulphur. Convenient phosphorous containing groups may comprise: phosphinyl (i.e. a '-PR3' radical where R independently denotes H or hydrocarbyl); phosphinic acid group(s) (i.e. a '-P(=O)(OH)2' radical); and phosphonic acid group(s) (i.e. a '-P(=O)(OH)3 ' radical).

Most preferred organic groups comprise one or more of the following carbon containing moieties: alkyl, alkoxy, alkanoyl, carboxy, carbonyl, formyl and/or combinations thereof; optionally in combination with one or more of the following heteroatom containing moieties: oxy, thio, sulphinyl, sulphonyl, amino, imino, nitrilo and/or combinations thereof. Organic groups include all chemically possible combinations in the same moiety of a plurality (preferably two) of the aforementioned carbon containing and/or heteroatom moieties (e.g. alkoxy and carbonyl if directly attached to each other represent an alkoxycarbonyl group).

The term 'hydrocarbo group' as used herein is a sub set of a organic group and denotes any univalent or multivalent moiety (optionally attached to one or more other moieties) which consists of one or more hydrogen atoms and one or more carbon atoms and may comprise one or more saturated, unsaturated and/or aromatic moieties. Hydrocarbo groups may comprise one or more of the following groups. Hydrocarbyl groups comprise univalent groups formed by removing a hydrogen atom from a hydrocarbon (for example alkyl). Hydrocarbylene groups comprise divalent groups formed by removing two hydrogen atoms from a hydrocarbon, the free valencies of

which are not engaged in a double bond (for example alkylene). Hydrocarbylidene groups comprise divalent groups (which may be represented by "R2C=") formed by removing two hydrogen atoms from the same carbon atom of a hydrocarbon, the free valencies of which are engaged in a double bond (for example alkylidene). Hydrocarbylidyne groups comprise trivalent groups (which may be represented by "RC≡"), formed by removing three hydrogen atoms from the same carbon atom of a hydrocarbon the free valencies of which are engaged in a triple bond (for example alkylidyne). Hydrocarbo groups may also comprise saturated carbon to carbon single bonds (e.g. in alkyl groups); unsaturated double and/or triple carbon to carbon bonds (e.g. in respectively alkenyl and alkynyl groups); aromatic groups (e.g. in aryl groups) and/or combinations thereof within the same moiety and where indicated may be substituted with other functional groups

The term 'alkyl' or its equivalent (e.g. 'alk') as used herein may be readily replaced, where appropriate and unless the context clearly indicates otherwise, by terms encompassing any other hydrocarbo group such as those described herein (e.g. comprising double bonds, triple bonds, aromatic moieties (such as respectively alkenyl, alkynyl and/or aryl) and/or combinations thereof (e.g. aralkyl) as well as any multivalent hydrocarbo species linking two or more moieties (such as bivalent hydrocarbylene radicals e.g. alkylene).

Any radical group or moiety mentioned herein (e.g. as a substituent) may be a multivalent or a monovalent radical unless otherwise stated or the context clearly indicates otherwise (e.g. a bivalent hydrocarbylene moiety linking two other moieties). However where indicated herein such monovalent or multivalent groups may still also comprise optional substituents. A group which comprises a chain of three or more atoms signifies a group in which the chain wholly or in part may be linear, branched and/or form a ring (including spiro and/or fused rings). The total number of certain atoms is specified for certain substituents for example C1 Norgano, signifies a organo moiety comprising from 1 to N carbon atoms. In any of the formulae herein if one or more substituents are not indicated as attached to any particular atom in a moiety (e.g. on a particular position along a chain and/or ring) the substituent may replace any H and/or may be located at any available position on the moiety which is chemically suitable and/or effective.

Preferably any of the organo groups listed herein comprise from 1 to 36 carbon atoms, more preferably from 1 to 18. It is particularly preferred that the number of carbon atoms in an organo group is from 1 to 12, especially from 1 to 10 inclusive, for example from 1 to 4 carbon atoms.

As used herein chemical terms (other than IUAPC names for specifically identified compounds) which comprise features which are given in parentheses - such as (alkyl)acrylate, (meth)acrylate and/or (co)polymer denote that that part in parentheses is optional as the context dictates, so for example the term (meth)acrylate denotes both methacrylate and acrylate.

Certain moieties, species, groups, repeat units, compounds, oligomers, polymers, materials, mixtures, compositions and/or formulations which comprise and/or are used in some or all of the invention as described herein may exist as one or more different forms such as any of those in the following non exhaustive list: stereoisomers (such as enantiomers (e.g. E and/or Z forms), diastereoisomers and/or geometric isomers); tautomers (e.g. keto and/or enol forms), conformers, salts, zwitterions, complexes (such as chelates, clathrates, crown compounds, cyptands / cryptades, inclusion compounds, intercalation compounds, interstitial compounds, ligand complexes, organometallic complexes, non stoichiometric complexes, π adducts, solvates and/or hydrates); isotopically substituted forms, polymeric configurations [such as homo or copolymers, random, graft and/or block polymers, linear and/or branched polymers (e.g. star and/or side branched), cross linked and/or networked polymers, polymers obtainable from di and/or tri valent repeat units, dendrimers, polymers of different tacticity (e.g. isotactic, syndiotactic or atactic polymers)]; polymorphs (such as interstitial forms, crystalline forms and/or amorphous forms), different phases, solid solutions; and/or combinations thereof and/or mixtures thereof where possible. The present invention comprises and/or uses all such forms which are effective as defined herein.

Polymers of the present invention may be prepared by one or more suitable polymer precursor(s) which may be organic and/or inorganic and comprise any suitable (co)monomer(s), (co)polymer(s) [including homopolymer(s)] and mixtures thereof which comprise moieties which are capable of forming a bond with the or each polymer precursor(s) to provide chain extension and/or cross-linking with another of the or each polymer precursor(s) via direct bond(s) as indicated herein.

Polymer precursors of the invention may comprise one or more monomer(s), oligomer(s), polymer(s); mixtures thereof and/or combinations thereof which have suitable polymerisable functionality.

A monomer is a substantially monodisperse compound of a low molecular weight (for example less than one thousand daltons) which is capable of being polymerised.

A polymer is a polydisperse mixture of macromolecules of large molecular weight (for example many thousands of daltons) prepared by a polymerisation method, where the macromolecules comprises the multiple repetition of smaller units (which may themselves be monomers, oligomers and/or polymers) and where (unless properties are critically dependent on fine details of the molecular structure) the addition or removal one or a few of the units has a negligible effect on the properties of the macromolecule.

A oligomer is a polydisperse mixture of molecules having an intermediate molecular weight between a monomer and polymer, the molecules comprising a small plurality of monomer units the removal of one or a few of which would significantly vary the properties of the molecule.

Depending on the context the term polymer may or may not encompass oligomer.

The polymer precursor of and/or used in the invention may be prepared by direct synthesis or (if the polymeric precursor is itself polymeric) by polymerisation. If a polymerisable polymer is itself used as a polymer precursor of and/or used in the invention it is preferred that such a polymer precursor has a low polydispersity, more preferably is substantially monodisperse, to minimise the side reactions, number of by-products and/or polydispersity in any polymeric material formed from this polymer precursor. The polymer precursor(s) may be substantially un-reactive at normal temperatures and pressures.

Except where indicated herein polymers and/or polymeric polymer precursors of and/or used in the invention can be (co)-polymerised by any suitable means of polymerisation well known to those skilled in the art. Examples of suitable methods comprise: thermal initiation; chemical initiation by adding suitable agents; catalysis; and/or initiation using an optional initiator followed by irradiation, for example with electromagnetic radiation (photo-chemical initiation) at a suitable wavelength such as UV and/or with other types of radiation such as electron beams, alpha particles, neutrons and/or other particles .

The substituents on the repeating unit of a polymer and/or oligomer may be selected to improve the compatibility of the materials with the polymers and/or resins in which they may be formulated and/or incorporated for the uses described herein. Thus the size and length of the substituents may be selected to optimise the physical entanglement or interlocation with the resin or they may or may not comprise other reactive entities capable of chemically reacting and/or cross linking with such other resins as appropriate.

Examples

The present invention will now be described in detail with reference to the following non limiting examples which are by way of illustration only.

The following abbreviations are used herein for various ingredients which are identified by chemical name and/or trade-name and optionally their manufacturer or supplier from whom they are available commercially.

"AA" denotes acrylic acid (CH ₂ =CHCO ₂ H). "AOT" denotes Aerosol ^® OT 75 the trade mark of an anionic surfactant available commercially from Sigma Chemical

"BA" denotes butyl acrylate

"CEA" denotes beta carboxy ethyl acrylate (β-CEA) an oligomer formed from AA.

"DM" denotes n-dodecyl mercaptane. "EA" denotes ethyl acrylate.

"EHA" denotes 2-ethyl hydroxy acrylate

"EO" denotes ethoxy (e.g. repeat unit in a polyether moiety).

"HIT" denotes Hitenol ^® BC 2020 a 20% aqueous solution of the polymerisible surfactant Hitenol ^® BC 20 (which is propenyl nonyl phenol ether sulfate with 20 mol EO) available commercially from Dai- lchi Kogyo Seiyaku under the preceding trade marks.

"KPS" denotes potassium persulfate.

"MA" denotes methyl acrylate.

"MAA" denotes methacrylic acid ( CH ₂ =C(CH ₃ )CO ₂ H ).

"NOR" denotes ethylimidazolidone methacrylate available commercially from Atofina under the trademark Norsocryl ^® N 104

"STY" denotes stryene

"t-BHP" denotes tert. butyl hydroxy peroxide.

"TSPP" denotes tetrasodium pyrophosphate.

Emulsions are prepared from the following monomer compositions as described below. The weight percentages are given to 3 s.f. therefore rounding errors mean percentages may not total 100%

TABLE I monomer composition weight % Example 1 Comp A Comp B

(i) EHA 79.3 % (423. 8 g), 60.7 % (298 g) 70.4 % (383.06 g) (i) STY (5.93% of i) 4.99 % (26.7 q) none 9.05 % (49.25 q) (11.4% of. T] (i) Sub-total 84.2 % (450. 5 q) 60.7 % (298 Q) 79.4 % (432.31 Q)

(ϋ) CEA 1.80 % (9.63 Q) none 1.77 % (9.63 g)

(ii) AA 1.00 % (5.35 g) 2.87 % (14.08 g) 1.21 % (6.6 g) (M) MAA none 2.05 %(10.06 a) none

(H) Sub-total 2.80 % (14.98 Q) 4.92 % (24.14 Q) 2.98 % (16.23 Q)

(iii) EA 12.5 % (66.9 g) - 12.1 % (65.67 g) (iii) MA none 14.2 % (69.51 g) none (iii) BA none 20.2 % (99.1 a) 5.53 % (30.1 a)

(iii) Sub-total 12.5 % (66.9 Q) 34.4 % (168.61 Q) 17.6 % (95.77 Q)

(iv) NOR 0.45 % (2.41 g) none none- Total 99.95 (534.76 q) 100.02 % (490.75 a) 99.98 % (544.31 a)

(v) HIT (aα 20%) 40.14 a 22.12 q 41.04 a

HIT solids 8.028 a 4.424 a 8.208 a

Example 1.

Preperation of latex

Water (21 1.8 g) and KPS (1.07 g) are added to a two litre jacketed glass polymerisation reactor equipped with a condenser, thermocouple and a blade agitator. In a separate container the following ingredients are mixed together for 40 minutes to form a monomer emulsion: HIT (40.14 g), TSPP (1.07 g), AOT (2.855 g), EHA (423.8 g), STY (26.7 g), EA (66.9 g) CEA (9.63 g) AA (5.35 g); NOR (2.41 g) and DM (0.73 g). Some of the monomer emulsion (16.2 g) is then added to the reactor. More initiator stock solution is prepared in a separate container by dissolving KPS (1.34 g) in water (446 g). The polymerization reactor is heated up to 78°C. Simultaneously both more monomer emulsion and KPS stock solution is slowly added to the reactor at respective rates of for monomer 3.6 g / minute for 200 minutes; and for KPS (using a syringe pump) 0.22 ml per hour for 210 minutes. The reactor temperature is held at 83°C for 210 minutes then raised to 86°C for 60 minutes, after which the reactor is cooled down to 55°C and the resultant latex is collected by filtration.

As comparative examples the following lattices (Comp A & B) were prepared without Norsocryl® 104 monomer

Comp A

To a 2L jacketed glass reactor equipped with a reflux condenser, thermocouple and twin blade agitator the following ingredients are added water (296.72 g), KPS (1.18 g) and HIT (7.37 g). In a separate vessel, a monomer pre-emulsion is prepared by mixing water (122.8 g) EHA (298 g), BA (99.1 g) MA (69.75 g), MAA (10.06 g), AA (14.08 g AA) and HIT (14.75 g). Separately, 61.77 g of KPS stock solution (0.94 wt. %

concentration) is prepared in water. The reactor is heated in a water bath and when the temperature reaches 79°C, the monomer pre-emulsion is added continuously at a rate of 3 g per minute for 200 minutes. The temperature is held at 83°C and the mixture agitated continuously at 240 rpm. Every 20 minutes during addition of the pre-emulsion KPS stock solution (6 g) is added to the reactor. After the pre-emulsion addition is complete, the reactor temperature is raised to 88°C, the mixture is agitated for a further 60 minutes and then the resultant latex is collected by filtration.

Comp B To a two liter jacketed glass reactor equipped with a condenser, thermocouple and an agitator, the following ingredients are added: water (200.5 g) and KPS (1.09 g). In a separate vessel a monomer pre-emulsion is prepared by mixing for 40 minutes: HIT (41.04 g), TSPP (0.93 g), EHA (383.06 g), BA (30.1 g), STY (49.25 g), EA (65.67 g), CEA (12.6 g), AA (6.6 g) and DM (0.27 g). Some of the monomer mixture (7.53 g) is then added added to the reactor. More initiator stock solution is prepared in a separate container by dissolving KPS (1.09 g) in water (42.24 g). The polymerization reactor is heated up to 78°C. Simultaneously both more monomer emulsion and KPS stock solution is slowly added to the reactor at respective rates of for monomer 3.73 g / minute for 200 minutes; and for KPS (using a syringe pump) 0.20 ml per hour for 210 minutes. The reactor temperature is held at 83°C for 210 minutes then raised to 86°C for 60 minutes, after which the reactor is cooled down to 55°C and the resultant latex is collected by filtration.

Characterisation of latex The latexes are characterised by the data in Table 1 where:

Solids % w/w denotes the percentage of solids by weight in the latex determined by placing known amount of latex into a weighed aluminum tin, drying at 150°C for 60 minutes to remove the water and weighing the tin again.

APS denotes the average particle size measured in nm using a Horiba laser light scattering particle size distribution analyzer model LA-910.

The pH (initial) denotes the pH of the latex after filtration measured by an Orion model

250 pH meter.

The pH (neut.) denotes the pH of the latex after neutralisation with ammonium hydroxide before being coated on a film for use in the tests below. Vis. denotes the Brookfield viscosity in 'cp' measured using a Brookfield viscometer LV

II+ with spindle #3 at 30 rpm.

Example Solids % w/w APS /nm pH (initial) pH (neut) Vise. / cp_ Ex 1 51.08 198 2.35 6.87 380

Comp A 46.79 86 2.34 7.85 1 124

Comp B 54.58 185 2.45 6.83 1828

Preparation & testing of coated film The Example 1 and Comp A & B are then each coated separately on a PET film of 1 mil thickness (for convenience each film also denoted Ex 1 , Comp A or Comp B). (PET denotes polyethylene terephthalate such as that available from DuPont under the trademark Mylar® which is a substrate of low surface energy) The coated film is dried for 10 minutes at ambient temperature and for 5 minutes at 90°C and then laminated with a release liner.

Water whitening test

To test water whitening resistance of the adhesive lattices the release liner is removed from the laminates to expose the polymer surface to water. The coated film is immersed in a water bath for 20 minutes (held at a constant temperature of 90°C) after which any color change in the film is evaluated visually rated on a scale from '0' to '5' (where a rating of '0' means that the film remains clear, transparent without any visible discoloration whereas a rating of '5' indicates that the film has turned matt white).

Example Colour change rating Ex 1 '0'

Comp A '0'

Comp B '0'

Peel test The Mylar films coated with each adhesive are applied to stainless steel (SS) and high density polyethylene substrate (HDPE). The film was peeled off after 20 min (unaged) and 24 hours (aged) using an lnstron machine to determine the peel values in Ib / inch.

Example SS (unaged) SS(aged) HDPE (unaged) HDPE (aged)

Ex 1 2.8 3.75 0.75 1.08

Comp A 1.35 1.99 0.40 0.38

Comp B 4.55 4.23 0.83 0.70

Shear test The shear value of each adhesive is determined by applying a strip of the coated film to an SS substrate with a region of overlap of 0.5 inch by 0.5 inch. A 1 Ib weight is hung from the laminate and the time taken for the laminate to fail is measured.

Example Shear (hrs)

Ex 1 90+ Comp B 3.2

Comp A is a waterborne adhesive which has excellent water whitening resistance but low adhesion on HDPE.

Comp B is a waterborne PSA which has good water whitening resistance and good adhesion on HDPE but low shear. The monomer composition is very similar as in Example 1 except there was no Norsocryl 104 used.