WO2021136705A1

WO2021136705A1 - A water-borne polymer composition, a method for making such and its application as removable pressure sensitive adhesive

Info

Publication number: WO2021136705A1
Application number: PCT/EP2020/087413
Authority: WO
Inventors: Chen Liu; Ke Xu; Jian Hua SUN; Shi Cheng LI; Jin Kun HAO; Jia Li WANG
Original assignee: Basf Se
Priority date: 2019-12-31
Filing date: 2020-12-21
Publication date: 2021-07-08
Also published as: CN114901703B; CN114901703A

Abstract

The present invention is related to a water-borne polymer composition, a method for preparing the same and the applications thereof. In particular, the present invention is related to a water-borne polymer which has bimodal or multimodal particle-size distribution. The water-borne polymer composition shows balanced performance in anchorage, loop tack and peel strength after aging. And, the composition is suitable for application as removable pressure sensitive adhesives.

Description

A water-borne polymer composition, a method for making such and its application as removable pressure sensitive adhesive

Field of Invention

The present invention is related to a water-borne polymer composition, a method for making such and its application as removable pressure sensitive adhesive (PSA). A removable PSA made from the water-borne polymer composition according to the current application shows balanced performance in anchorage, loop tack and peel strength. More particularly, the peel strength of the PSA does not increase significantly after aging.

Background

Pressure sensitive adhesives (PSAs) are used in a variety of products, including labels, tapes, laminates, etc., to adhere one substrate with another. The adhesive shall exhibit certain initial anchorage and superior tack performance when applied onto a substrate and be easily removable when desired. For many of the adhesive applications, the PSA is applied onto a substrate at a relative low temperature and the working condition of the finished product remains the same. However, adhesives may expose to high temperature for a long period of time which will result in aging phenomenon. Many of the current available adhesives, which demonstrate good anchorage, show significant increase of peel strength after aging and such increase may cause paper tear and/or undesirable adhesive transfer onto the substrate. And the increase of peel strength after aging may make the adhesive not removable.

The abovementioned issue has not been well studied. Instead, most of the development effort has been focused on improving the heat resistant properties of PSA (i.e. maintaining or enhancing anchorage properties under high temperature environment). More specifically, the effort has been directed to improve the performance of polymer emulsions which are major components in PSAs. For example, CN101974299B disclosed emulsions with 70-95 parts soft monomers, 1-20 parts hard monomers, 1-10 parts functional monomers, 0.5-20 parts reactive tackifying agent, 0.2-6 parts reactive emulsifier, etc. The resulted emulsion shows excellent anchorage and heat resistant properties. However, no information about the peel strength after aging was disclosed.

Another technical solution to improve the heat resistant property is adding special surfactants to polymer emulsions. For example, WO2018184852 disclosed a polymer emulsion comprising at least one monomer selected from acrylic and vinylic monomers, and a mixture of surfactants comprising a phosphate surfactant selected from alkoxylated alkyl phosphate ester acids or salts, and at least one of the following surfactants: a) a surfactant selected from alkoxylated alcohol sulfate metal M salts b) a surfactant selected from C4-C18 dialkyl diesters and/or C4-C18 mono alkyl esters of sulfonated C4-C8 dicarboxylic acid metal M salts.

The resulted emulsion contains monomodal particles and shows improved thermal stability. However, no information about the peel strength after aging was disclosed, neither.

Therefore, it remains a challenge to find solutions that can render an emulsion which is suitable for making removable PSA with balanced performance in anchorage, loop tack and peel strength. In addition, it’s even more challenge to maintain the peel strength of the PSA at a low level after aging.

Summary of the Invention

One approach to solve the abovementioned challenge is to add at least one specific surfactant into the emulsions and/or controlling the particle size distribution of polymer emulsions. One object of the current invention is to provide a water-borne polymer composition suitable for making removable PSAs which show balanced performance in anchorage, loop tack and peel strength. In addition, the removable PSA made by emulsion according to the present invention shows relative low peel strength even after aging. The water-borne polymer composition comprises A polymer synthesized with a) At least 85 wt%, based on the total weight of the polymer, of one or more hydrophobic ethylenically unsaturated monomer, b) At least 0.2 wt% and no more than 15 wt%, based on the total weight of the polymer, of one or more hydrophilic ethylenically unsaturated monomer;

Wherein the composition has a bimodal or multimodal particle-size distribution.

In a preferred embodiment, the water-borne polymer composition further comprises at least one emulsifier selected from compounds of the formula (I), (II) or a mixture thereof [R¹0(A0)_m][R²0(A0)_n]P(=0)(0M¹) (I)

R (A0)_mP(=0)(0M¹)(0M²) (II)

In which R¹ and R² are independently a C6-C30 alkyl, benzene and benzene derivative, m and n are independently an integer from 0 to 20, AO is alkyleneoxy, and M¹ and M² are independently a H or cationic ion.

Another object of the current invention is to provide a method for making the water borne polymer composition.

A third object of the current invention is to provide a removable PSA comprising said polymer composition. The PSA may be applied in an article, such as a tape, a label, a wide format protective film, a graphic film, etc. DETAILED DESCRIPTION OF THE INVENTION

Unless otherwise specified, all terms/terminology/nomenclatures used herein have the same meaning as commonly understood by the skilled person in the art to which this invention belongs to.

Expressions “a”, “an” and “the”, when used to define a term, include both the plural and singular forms of the term.

The term “polymer” or “polymers”, as used herein, includes both homopolymer(s), that is, polymers prepared from a single reactive compound, and copolymer(s), that is, polymers prepared by reaction of at least two polymer forming reactive, monomeric compounds.

The term “multimodal particle-size distribution” means in a polymer emulsion particles show at least two different major peak particle sizes and at least 85 wt% of particles have a particle size of either one of the at least two different major peak particle sizes. And, the term “bimodal particle-size distribution” means in a polymer emulsion particles show two different major peak particle sizes and at least 95 wt% of particles have a particle size of either one of the two major peak particle sizes.

The designation (meth)acrylate and similar designations are used herein as an abbreviated notation for “acrylate and/or methacrylate”.

Within the context of the present application, the term Fox Tg refers to a glass transition temperature (Tg) as calculated according to the following Fox equation as disclosed in T.G. Fox, Bulletin of the American Physical Society, Volume 1, Issue No. 3, page 123 (1956):

1/Tg = Wi/Tgi + W2/Tg2 + ··· + W_n/Tg_n wherein

Wi, W2, ... W_n, are the mass fractions of the monomers 1, 2, . . . n, respectively, and

Tgi, Tg₂, ...Tg_n, are the glass transition temperatures of homopolymers of the monomers 1, 2, . . . n in degrees Kelvin, respectively.

The Tg values for homopolymers of the majority of monomers are known and are listed in, for example, Ullmann's Ecyclopedia of Industrial Chemistry, Vol. 5, Vol. A21, page 169, VCH Weinheim, 1992. Other sources of glass transition temperatures of homopolymers include, for example, J. Brandrup, E. H. Immergut, Polymer Handbook, 1st Edition, J. Wiley, New York 1966, 2nd Edition, J. Wley, New York 1975, and 3rd Edition, J. Wley, New York 1989.

All percentages and ratios denote weight percentages and weight ratios unless otherwise specified. The term “weight average particle diameter” refers to the weight average particle size of a material as determined using capillary hydrodynamic fractionation (CHDF) with a Matec CHDF 2000 chromatography system (Matec Applied Sciences, Northborough, MA).

One object of the present invention relates to a water-borne polymer composition suitable for making PSAs which show balanced performance in anchorage, loop tack and peel strength after aging. The composition comprises:

A polymer synthesized with a) At least 85 wt%, based on the total weight of the polymer, of one or more hydrophobic ethylenically unsaturated monomer, b) At least 0.2 wt% and no more than 15 wt%, based on the total weight of the polymer, of one or more hydrophilic ethylenically unsaturated monomer;

Wherein the composition has a bimodal or multimodal particle-size distribution.

The at least one hydrophobic monoethylenically unsaturated monomer (a) may be selected from, but not limited to, (meth)acrylate monomers, (meth)acrylonitrile monomers, styrene monomers, vinyl alkanoate monomers, monoethylenically unsaturated di-and tricarboxylic ester monomers and any mixture thereof.

Particularly, the (meth)acrylate monomers may be Ci-Ci9-alkyl (meth)acrylates, for example, but not limited to, methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-octyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate (i.e. lauryl (meth)acrylate), tetradecyl (meth)acrylate, oleyl (meth)acrylate, palmityl (meth)acrylate, stearyl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, phenyl (meth)acrylate and a mixture thereof.

Particularly, the styrene monomers may be unsubstituted styrene or C1-C6-alkyl substituted styrenes, for example, but not limited to, styrene, a-methylstyrene, ortho-, meta- and para-methylstyrene, ortho-, meta- and para-ethylstyrene, o,p- dimethylstyrene, o,r-diethylstyrene, ispropylstyrene, o-methyl-p-isopropylstyrene or any mixture thereof.

Particularly, the vinyl alkanoate monomers may be vinyl esters of C2-Cn-alkanoic acids, for example, but not limited to, vinyl acetate, vinyl propionate, vinyl butanoate, vinyl valerate, vinyl hexanoate, vinyl versatate or a mixture thereof.

In addition, the monoethylenically unsaturated di-and tricarboxylic ester monomers may be full esters of monoethylenically unsaturated di-and tricarboxylic acids, for example, but not limited to, diethyl maleate, dimethyl fumarate, ethyl methyl itaconate, or any mixture thereof. In a preferred embodiment according to the present invention, one or more C1-C12- alkyl (meth)acrylates, such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate, styrene or a mixture thereof is chosen as the at least one hydrophobic monoethylenically unsaturated monomer (a).

The hydrophobic monomer may account for, based on the total weight of the polymer, at least 85 wt%, preferably at least 90 wt%, more preferably at least 95% by weight.

The at least one hydrophilic monoethylenically unsaturated monomer (b) may be monoethylenically unsaturated monomers containing at least one functional group selected from the group consisting of carboxyl, carboxylic anhydride, sulfonic acid, phosphoric acid, hydroxyl and amide.

Particularly, the hydrophilic monoethylenically unsaturated monomer (b) includes, but not limited to, monoethylenically unsaturated carboxylic acids, such as (meth)acrylic acid, itaconic acid, fumaric acid, citraconic acid, sorbic acid, cinnamic acid, glutaconic acid and maleic acid; monoethylenically unsaturated carboxylic anhydride, such as itaconic acid anhydride, fumaric acid anhydride, citraconic acid anhydride, sorbic acid anhydride, cinnamic acid anhydride, glutaconic acid anhydride and maleic acid anhydride; monoethylenically unsaturated amides, especially N-alkylolamides, such as (meth)acrylamide, N-methylol (meth)acrylamide, 2-hydroxyethyl (meth)acrylamide; and hydroxyalkyl esters of monoethylenically unsaturated carboxylic acids, such as hydroxyethyl (meth)acrylate and hydroxypropyl (meth)acrylate.

In a preferred embodiment according to the present invention, acrylic acid, methacrylic acid, itaconic acid, acrylamide, methacrylamide or a mixture thereof is preferred as the at least one hydrophilic monoethylenically unsaturated monomer (b).

The hydrophilic monomer may account for, based on the total weight of the polymer, at least 0.2 wt% and no more than 15 wt%, preferably at least 0.5 wt% and no more than 10 wt%, and more preferably at least 1 wt% and no more than 5 wt%.

The polymer may be synthesized with additional one or more crosslinking monomers (c). The crosslinking monomers may help improve the shear performance, which is an important performance criterion in some adhesive applications. However, the weight ratio of the crosslinking monomers shall be carefully controlled. A high weight ratio of crosslinking monomers may deteriorate the loop tack performance of the PSA. The crosslinking monomers can be chosen from di- or poly-isocyanates, polyaziridines, polycarbodiimide, polyoxazolines, glyoxals, triols, epoxy molecules, organic silanes, carbamates, diamines and triamines, hydrazides, carbodiimides and multi- ethylenically unsaturated monomers. In the present invention, suitable crosslinking monomers include, but not limited to, glycidyl (meth)acrylate, N- methylol(meth)acrylamide, (isobutoxymethyl)acrylamide, vinyltrialkoxysilanes such as vinyltrimethoxysilane; alkylvinyldialkoxysilanes such as dimethoxymethylvinylsilane; (meth)acryloxyalkyltrialkoxysilanes such as (meth)acryloxyethyltrimethoxysilane, (3- acryloxypropyl)trimethoxysilane and (3-methacryloxypropyl)trimethoxysilane , allyl methacrylate, diallyl phthalate, 1,4-butylene glycol dimethacrylate, 1 ,2-ethylene glycol dimethacrylate, 1 ,6-hexanediol diacrylate, divinyl benzene or any mixture thereof.

The crosslinker can be added in an amount of, based on the total weight of the polymer, no more than 5 wt%, preferably no more than 3 wt%, and more preferably no more than 1 wt%.

In addition, the polymer may be synthesized with the presence of at least one chain transfer agent. Chain transfer agents are frequently used to regulate the molecular weight of polymers. Chain transfer agents may include, but not limited to, compounds containing a thiol group, for example mercaptans, such as without limitation, ethyl mercaptan, n-propyl mercaptan, n-butyl mercaptan, isobutyl mercaptan, t-butyl mercaptan, n-amyl mercaptan, isoamyl mercaptan, t-amyl mercaptan, n-hexyl mercaptan, cyclohexyl mercaptan, n-octyl mercaptan, n-decyl mercaptan, n-dodecyl mercaptan, mercapto carboxylic acids and their esters, such as without limitation, 2- ethylhexyl thioglycolate, methyl mercaptopropionate and 3-mercaptopropionic acid, alcohols, such as isopropanol, isobutanol, lauryl alcohol and t-octyl alcohol, halogenated compounds such as carbon tetrachloride, tetrachloroethylene, tricholoro- bromoethane, and any combination thereof.

The chain transfer agent may be added in an amount of, based on the total weight of the polymer, no more than 1 wt%, preferably no more than 0.5 wt%, and more preferably no more than 0.2 wt%.

The resulted polymer may have an overall Fox Tg in the range of -15 to -65 °C, preferably -20 to -60 °C and more preferably -25 to -55 °C.

According to one embodiment of the present invention, the emulsion may have a multimodal particle-size distribution. The emulsion according to the present invention contains at least one polymer particle with a weight average particle diameter in the range of 80 to 550 nm, preferably in the range of 100 to 500 nm and more preferably in the range of 120 to 480 nm. The emulsion according to the present invention also contains at least another polymer particle with a weight average particle diameter in the range of 400 to 1 ,000 nm, preferably in the range of 450 to 900 nm and more preferably in the range of 480 to 800 nm. The difference between the weight average particle diameter of the at least two polymer particles are at least 200 nm, preferably at least 250 nm and more preferably at least 300 nm. And, the weight ratio of each polymer particle, in terms of the total weight of all polymer particles, is at least 5 wt%.

In one embodiment, at least 40%, by weight, of the polymer particles have a weight average particle diameter of in the range of 400 to 1,000 nm and no more than 60%, by weight, of the polymer particles have a weight average particle diameter in the range of 80 to 550 nm; preferably at least 45%, by weight, of the polymer particles have a weight average particle in the range of 450 to 900 n and no more than 55%, by weight, of the polymer particles have a weight average particle diameter in the range of 100 to 500 nm; more preferably at least 50%, by weight, of the polymer particles have a weight average particle diameter in the range of 480 to 800 nm and no more than 50%, by weight, of the polymer particles have a weight average particle diameter in the range of 120 to 480 nm.

In another embodiment, at least 80%, by weight, of the polymer particles have a weight average particle diameter in the range of 400 to 1,000 nm and no more than 20%, by weight, of the polymer particles have a weight average particle diameter in the range of 100 to 500 nm; preferably, at least 85%, by weight, of the polymer particles have a weight average particle diameter in the range of 450 to 800 and no more than 15%, by weight, of the polymer particles have a weight average particle diameter in the range of 150 to 450.

According to a preferred embodiment, the water-borne polymer composition further comprises at least one emulsifier selected from compounds of the formula (I), (II) or a mixture thereof:

[R¹0(A0)m][R²0(A0)n]P(=0)(0M¹) (I)

R (AO)mP(=0)(OM¹)(OM²) (II)

The at least one surfactant of formula (I) or of formula (II) may be added into the water borne polymer composition. The R¹ and R² are independently a C6-C30 alkyl, benzene and benzene derivative. The C6-C30 alkyl can be chosen from linear/branched/cyclic C6-C30 alkyls, preferably linear/branched/cyclic C8-C25 alkyls, more preferably linear/branched/cyclic C8-C20 alkyls. Benzene and benzene derivative can be chosen from benzene, C1-C15 alkyl benzyl, C1-C20 alkyl benzoate and aryloxy. Preferably, benzene and benzene derivative can be chosen from benzene, C2-C12 alkyl benzyl, C2-C15 alkyl benzoate and aryloxy. More preferably, benzene and benzene derivative can be chosen from benzene, C4-C8 alkyl benzyl, C4-C10 alkyl benzoate and aryloxy. The number m and n are independently an integer from 0 to 20, preferably from 1 to 15, more preferably 1 to 10 and most preferably 1 to 6. AO is alkyleneoxy, which can be chosen from (-CH2CH2O-), (-CH2CH2CH2O-) and (-CH₂(CH₃)CHO-). M¹ and M² are independently a H or cationic ion, such as Li⁺, Na⁺, K⁺ and NhUT Many of the abovementioned surfactant is commercially available, such as Rhodafac RS410, RS610, RS710 and PE3501 (from Solvay) and Disponil FEP 3825 PN, Disponil FEP 6300 and Maphos 24T (from BASF), and TERIC 305 (from Huntsman), etc.

A surfactant of formula (I) or formula (II) may be used alone or in combination. The surfactant of formula (I) or formula (II) or in combination may be added in an amount of, based on the total weight of the water-borne polymer composition, 0.2-10 wt%, preferably 0.5-8 wt%, more preferably 1-5 wt% and most preferably 1.5-4 wt%. The least one surfactant of formula (I) (phosphate diester) or of formula (II) (phosphate monoester) may be added into the polymerization process or after the completion of polymerization process or in both processes.

Besides surfactants of formula (I) or formula (II), other suitable surfactants may also be used. Those surfactants include, but not limited to, non-reactive anionic and/or nonionic surfactants and polymerizable surfactants. In particular, the addition of extra polymerizable surfactants can be beneficial. Polymerizable surfactants, also called a reactive surfactant, containing at least one ethylenically unsaturated functional group. Suitable polymerizable surfactants for example include, but are not limited to, allyl polyoxyalkylene ether sulfate salts such as sodium salts of allyl polyoxyethylene alkyl ether sulfate, allyl alkyl succinate sulfonate salts, allyl ether hydroxyl propanesulfonate salts such as sodium salts, polyoxyethylene styrenated phenyl ether sulfate salts such as ammonium salts, for example DKS Hitenol^® AR 1025 and DKS Hitenol^® AR 2020, polyoxyethylene alkylphenyl ether sulfate ammonium salts, and polyoxyethylene allyloxy nonylphenoxypropyl ether, ADEKA REASOAP SR- 1025, 2025, 3025.

The total amount of surfactant in the composition may be in an amount of, based on the total weight of the water-borne polymer composition, 0.2-15 wt%, preferably 0.5- 10 wt%, more preferably 1-8 wt% and most preferably 1.5-5 wt%.

The composition according to the present invention may have a solid content in the range of 10% to 70% by weight, preferably 20% to 60% by weight, more preferably 30 to 60% by weight, and most preferably 40 to 60 % by weight.

Another object of the current invention is to provide a method to make the water-borne polymer composition. Emulsion with bimodal or multimodal particle-size distribution is known to have relatively low viscosity. The process for making emulsions with bimodal or multimodal size distribution can be found in W02002092637, US8030395B2, US9518199B2 and US6706356B2. Many techniques to make water-borne polymer emulsions known to the skilled person in the art may be applied to make the composition. One method is applying the seed polymerization, such as the procedure disclosed in US6028135A. Basically, some seeds are added into the reaction system first and the polymerization is carried out with the presence of seed. Another method is to conduct polymerization by adding the monomers following specific procedures, such as the procedure described in W0199807767. Many other methods, such as those taught in US4657966A, US 4247438A, US5498655A, US4501845, US5990228, etc may be applied as well.

The polymerization may be conducted either as a batch operation or in the form of a feed process (i.e. the reaction mixture is fed into the reactor in a staged or gradient procedure). Feed process is a preferred process. In such a process, a small amount of reactant is introduced into a reactor as an initial charge and heated to the polymerization temperature. Then the major polymerization mixture, in combination of initiators, is supplied to the reactor, usually by way of two or more spatially separate feed streams. After the completion of the feeding, the reaction is further carried out for another 10 to 30 min and, optionally, followed by complete or partial neutralization of the mixture. Afterwards, the reaction mixture may be subject to oxidants, neutralizing agents, etc.

The emulsion polymerization may be carried out in the presence of various common initiating systems, including but not limited to a thermal or redox initiator. The initiator is usually used in an amount of no more than 10% by weight, preferably 0.02 to 5% by weight, more preferably 0.1 to 1.5 wt%, based on the total weight of all monomers.

Thermal initiators, such as peroxides, persulfates and azo compounds, are generally used. Peroxides, which may be used include, but are not limited to, inorganic peroxides, such as hydrogen peroxide, or peroxodisulfates, or organic peroxides, such as tert-butyl, p-menthyl or cumyl hydroperoxide, tert-butyl perpivalate, and dialkyl or diaryl peroxides, such as di-tert-butyl or di-cumyl peroxide. Azo compounds which may be used, include, but not limited to, 2,2^'-azobis(isobutyronitrile), 2,2^'-azobis(2,4- dimethylvaleronitrile). Among others, sodium persulfate (SPS), potassium persulfate (KPS), ammonium persulfate (APS), 2,2^'-azobis(amidinopropyl) dihydrochloride (AIBA, V-50 TM), and 4,4'-azobis(4-cyanovaleric acid) (ACVA , V501) are preferred as the thermal initiator.

A redox initiator usually comprises an oxidizing agent and a reducing agent. Suitable oxidizing agents include the abovementioned peroxides. Suitable reducing agents may be alkali metal sulfites, such as potassium and/or sodium sulfite, or alkali metal hydrogensulfites, such as potassium and/or sodium hydrogensulfite. Preferable redox initiators include an oxidizing agent selected from the group consisting of t- butylhydroperoxide and hydrogen peroxide, and a reducing agent selected from ascorbic acid, sodium formaldehyde sulfoxylate, sodium acetone bisulfite and sodium metabisulfite (sodium disulfite).

The polymerization may be carried out and maintained at a temperature lower than 100 °C throughout the course of the reaction. Preferably, the polymerization is carried out at a temperature between 60 °C and 95 °C. Depending on various polymerization conditions, the polymerization may be carried out for several hours, for example 2 to 8 hours.

An organic base and/or inorganic base may be added into the polymerization system as a neutralizer during the polymerization or after the completion of such process. Suitable neutralizers include, but are not limited to, inorganic bases such as ammonia, sodium/potassium hydroxide, sodium/potassium carbonate or any combination thereof. Organic bases such as dimethyl amine, diethyl amine, triethyl amine, monoethanolamine, triethanolamine, or a mixture thereof can also be used as the neutralizer. Among others, sodium hydroxide, ammonia, dimethylaminoethanol, 2- amino-2-methyl-1 -propanol or any mixture thereof is preferable as the neutralizer useful for the polymerization process. Upon the addition of a neutralizer, pH of the final polymer emulsion shall be in the range of 6.0 to 10.0, preferably in the range of 6.5 to 9.5, more preferably in the range of 7.0 to 9.0.

A third object of the current invention is to provide a removable PSA comprising said composition. The water-borne polymer emulsions according the present invention may be formulated into a PSA composition by various processes known to the skilled person in the art. There is no particular preference for the preparation of the PSA composition. For example, the polymer composition may be mixed with tackifiers, biocides, wetting agents, defoamers, etc. Examples of suitable tackifiers include, but not limited to, natural resins, such as rosins and their derivatives, hydrocarbon resins, coumarone-indene resins, and polyterpene resins. Tackifiers may be added in an amount of 0 to 100 parts by weight, preferably 0 to 30 parts by weight, per 100 parts by weight of polymer (solids/solids). Suitable biocides include, but not limited to, Kathon LX and MBS5050. Biocides may be added in an amount of 0.1-0.5%. An example of a suitable wetting agent includes, but not limited to, Lumiten ISC, Surfynol SE, PLURONIC and the like. Wetting agent may be added in an amount of 0.2-15%. Examples of defoamers include, but not limited to, Foamaster MO 2190, Drewplus T- 1201, Drewplus 1-191 and Rhodoline 6681. Defoamer may be added in an amount of 0-0.2%. The percentage of wetting agent, biocide, and deformer are the percentage of wet (additives) to wet (emulsions).

The present invention is further demonstrated and exemplified in the Examples, however, without being limited to the embodiments described in the Examples.

EXAMPLES

Disponil^® FES 27, sodium lauryl ether sulphate, from BASF (hereinafter noted as FES 27)

Disponil^® LDBS23: alkyl benzene sulphonate surfactant, from BASF (hereinafter noted as LDBS23)

Rhodafac^® RS610, phosphate ester surfactant, from Solvay (hereinafter noted as RS- 610)

Rhodacal^® DS-4, Sodium Dodecyl (branched) Benzene Sulfonate surfactant, from Solvay

Adeka SR-1025, Reactive surfactant, from Adeka

Disponil^® FEP 3825 PN, phosphoric acid ester, from BASF (hereinafter noted as Disponil FEP)

Lumiten l-SC, sodium sulphosuccinate/ isotridecanol ethoxylate in water, from BASF Foamaster MO 2190, blend of silica and oil, from BASF

All experiments described hereinafter were performed at a temperature of 23 °C unless otherwise specified. All the polymerization reactions were performed under nitrogen gas protection unless otherwise specified.

Preparation of polymer emulsions

Emulsion 1

An emulsion feed was prepared by combining 10.84 g FES 27, 12.73 g LDBS 23, 165.46 g Dl water, 7.03 g sodium hydroxide solution (32.5 wt% solid content), 360 g ethylhexyl acrylate, 230.76 g butyl acrylate, 6 g acrylic acid, 2.4 g acrylamide, 0.42 g 1,4-butanediol diacrylate and 0.42 g t-dodecyl mercaptan in a vessel, and emulsified under stirring for 10 min at a speed of 500 rpm.

To a 2000 ml flask reactor equipped with a stirrer, a condenser and feeding ports, 112.82 g Dl water and 2.93 g ascorbic acid solution (10 wt% solid content) were added as an initial charge. Then the mixture in the reactor was heated to 85 °C in 30 min with stirring at a speed of 500 rpm and temperature was kept as such thereafter. Meanwhile, 5.02 g sodium persulfate aqueous solution (7 wt% solid content) was added into the flask over 30 min.

Then, the emulsion feed was added into the reactor over 220 min and another 14.22 g sodium persulfate aqueous solution (7 wt% solid content) was added into the flask over 240 min. 30 min after the completion of sodium persulfate aqueous solution feeding, 15.77 g sodium acetonebisulfite (13 wt% solid content) and 12.3 g tert-butyl hydroperoxide (10 wt% solid content) are added over 60 min to remove the residual monomers.

The resulted emulsion has a solid content of 59.8 wt%, a pH of 6.5, a viscosity of 100- 250 mPa.s and a multimodal polymer particle-size distribution with one peak particle size at 430 nm which accounts for 39.8% of the total weight of particles and another peak particle size at 760 nm which accounts for 50.2% of the total weight of particles.

Emulsion 2

An emulsion feed was prepared by combining 10.84 g FES 27, 12.73 g LDBS 23, 165.46 g Dl water, 7.03 g sodium hydroxide solution (32.5 wt% solid content), 360 g ethylhexyl acrylate, 231.18 g butyl acrylate, 6 g acrylic acid, 2.4 g acrylamide, 0.42 g 1,4-butanediol diacrylate, 0.42 g t-dodecyl mercaptan and 3 g RS610 in a vessel, and emulsified under stirring for 10 min at a speed of 500 rpm. All other procedures remain the same as described in Emulsion 1.

The resulted emulsion has a solid content of 60.1 wt%, a pH of 6.6, a viscosity of 100- 250 mPa.s and a multimodal polymer particle-size distribution with one peak particle size at 410 nm which accounts for 38.5% of the total weight of particles and another peak particle size at 760 nm which accounts for 51.6% of the total weight of particles.

Emulsion 3

An emulsion feed was prepared by combining 10.84 g FES 27, 12.73 g LDBS 23, 165.46 g Dl water, 7.03 g sodium hydroxide solution (32.5 wt% solid content), 354 g ethylhexyl acrylate, 231.18 g butyl acrylate, 6 g acrylic acid, 2.4 g acrylamide, 6 g styrene, 0.42 g 1,4-butanediol diacrylate and 0.42 g t-dodecyl mercaptan in a vessel, and emulsified under stirring for 10 min at a speed of 500 rpm.

All other procedures remain the same as described in Emulsion 1.

The resulted emulsion has a solid content of 60.3 wt%, a pH of 6.8, a viscosity of 100- 250 mPa.s and a multimodal polymer particle-size distribution with one peak particle size at 405 nm which accounts for 38.2% of the total weight of particles and another peak particle size at 740 nm which accounts for 51.4% of the total weight of particles.

Emulsion 4

An emulsion feed was prepared by combining 10.84 g FES 27, 12.73 g LDBS 23, 165.46 g Dl water, 7.03 g sodium hydroxide solution (32.5 wt% solid content), 300 g ethylhexyl acrylate, 230.76 g butyl acrylate, 6 g acrylic acid, 2.4 g acrylamide, 60 g methyl methacrylate, 0.42 g 1,4-butanediol diacrylate and 0.42 g t-dodecyl mercaptan in a vessel, and emulsified under stirring for 10 min at a speed of 500 rpm.

All other procedures remain the same as described in Emulsion 1.

The resulted emulsion has a solid content of 60.2 wt%, a pH of 6.6, a viscosity of 100- 250 mPa.s and a multimodal polymer particle-size distribution with one peak particle size at 410 nm which accounts for 37.9% of the total weight of particles and another peak particle size at 730 nm which accounts for 52.6% of the total weight of particles.

Emulsion 5

An emulsion feed was prepared by combining 10.84 g FES 27, 12.73 g LDBS 23, 165.46 g Dl water, 7.03 g sodium hydroxide solution (32.5 wt% solid content), 240 g ethylhexyl acrylate, 230.76 g butyl acrylate, 6 g acrylic acid, 2.4 g acrylamide, 120 g methyl methacrylate, 0.42 g 1,4-butanediol diacrylate and 0.42 g t-dodecyl mercaptan in a vessel, and emulsified under stirring for 10 min at a speed of 500 rpm.

All other procedures remain the same as described in Emulsion 1. The resulted emulsion has a solid content of 60.7 wt%, a pH of 6.9, a viscosity of 100- 250 mPa.s and a multimodal polymer particle-size distribution with one particle size peak at 390 nm which accounts for 36.4% of the total weight of particles and another particle size peak at 710 nm which accounts for 53.1% of the total weight of particles.

Emulsion 6

An emulsion feed was prepared by combining 12.42 g Rhodacal DS-4, 19.04 g Adeka SR-1025, 209.44 g Dl water, 37.13 g sodium hydroxide solution (10 wt% solid content), 574.25 g ethylhexyl acrylate, 366.81 g butyl acrylate, 7.14 g acrylic acid, 7.14g acrylamide, and 0.67 g t-dodecyl mercaptan in a vessel, and emulsified under stirring for 10 min at a speed of 500 rpm.

To a 2000 ml flask reactor equipped with a stirrer, a condenser and feeding ports, 133.28 g Dl water were added as initial charge. Then the mixture in the reactor was heated to 85 °C in 30 min with stirring at a speed of 500 rpm and temperature was kept as such thereafter. Meanwhile, 8.16 g sodium persulfate aqueous solution (7 wt% solid content) was added into the flask over 5 min.

Then, the emulsion feed was added into the reactor over 210 min and another 29.92 g sodium persulfate aqueous solution (7 wt% solid content) was added into the flask over 220 min. 30 min after the completion of sodium persulfate aqueous solution feeding, 25.63 g sodium acetonebisulfite (13 wt% solid content) and 19.99 g tert-butyl hydroperoxide (10 wt% solid content) are added over 60 min to remove the residual monomers.

The resulted emulsion has a solid content of 63 wt%, a pH of 5.5, a viscosity of 200- 300 mPa.s and a bimodal polymer particle-size distribution with one peak particle size at 200 nm which accounts for 11 % of the total weight of particles and another peak particle size at 500 nm which accounts for 89% of the total weight of particles.

Emulsion 7

An emulsion feed was prepared by combining 10 g FES 27, 12.74 g LDBS 23, 194.4 g Dl water, 354 g ethylhexyl acrylate, 231.6 g butyl acrylate, 6 g acrylic acid, 2.4 g acrylamide and 6 g styrene in a vessel, and emulsified under stirring for 10 min at a speed of 500 rpm.

To a 2000 ml flask reactor equipped with a stirrer, a condenser and feeding ports, 151.2 g Dl water and 1.31 g Seed 6772 (Pre-product 6772, a polystyrene seed with a diameter of 30 nm, from BASF, 33 wt% solid content) were added as an initial charge. Then the mixture in the reactor was heated to 85 °C in 30 min with stirring at a speed of 500 rpm and temperature was kept as such thereafter. Meanwhile, 3.09 g sodium persulfate aqueous solution (7 wt% solid content) was added into the flask over 30 min. Then, the emulsion feed was added into the reactor over 255 min and another 13.11 g sodium persulfate aqueous solution (7 wt% solid content) was added into the flask over 270 min. 30 min after the completion of sodium persulfate aqueous solution feeding, 14.54 g sodium acetonebisulfite (13 wt% solid content) and 11.34 g tert-butyl hydroperoxide (10 wt% solid content) are added over 60 min to remove the residual monomers.

The resulted emulsion has a solid content of 54.9 wt%, a pH of 6.1, a viscosity of 100- 500 mPa.s and a monomodal polymer particle-size distribution with a peak particle size at 280 nm.

Emulsion 8

An emulsion feed was prepared by combining 10 g FES 27, 12.74 g LDBS 23, 194.4 g Dl water, 353.58 g ethylhexyl acrylate, 231.6 g butyl acrylate, 6 g acrylic acid, 2.4 g acrylamide, 6 g styrene and 0.42 g 1 ,4-butanediol diacrylate in a vessel, and emulsified under stirring for 10 min at a speed of 500 rpm.

To a 2000 ml flask reactor equipped with a stirrer, a condenser and feeding ports, 151.2 g Dl water and 1.31 g Seed 6772 (Pre-product 6772, a polystyrene seed with a diameter of 30 nm, from BASF, 33 wt% solid content) were added as an initial charge. Then the mixture in the reactor was heated to 85 °C in 30 min with stirring at a speed of 500 rpm and temperature was kept as such thereafter. Meanwhile, 3.09 g sodium persulfate aqueous solution (7 wt% solid content) was added into the flask over 30 min.

Then, the emulsion feed was added into the reactor over 255 min and another 13.11 g sodium persulfate aqueous solution (7 wt% solid content) was added into the flask over 270 min. 30 min after the completion of sodium persulfate aqueous solution feeding, 14.54 g sodium acetonebisulfite (13 wt% solid content) and 11.34 g tert-butyl hydroperoxide (10 wt% solid content) are added over 60 min to remove the residual monomers.

The resulted emulsion has a solid content of 53.8 wt%, a pH of 6.2, a viscosity of 100- 500 mPa.s and a monomodal polymer particle-size distribution with a peak particle size at 265 nm.

Formulation of PSAs

PSA 1

Appropriate amount of ammonia solution (20 wt%) was added to emulsion 1 as prepared above to neutralize the pH to 8. To 500 g of the neutralized solution (50% solid content), 2.5 g of Lumiten l-SC solution, 0.5 g of Foamaster MO 2190 and 15.5 g of RS 610 were added. The resulted mixture was stirred for 30 min at a speed of 500 rpm. PSA 2

Appropriate amount of ammonia solution (20 wt%) was added to emulsion 1 as prepared above to neutralize the pH to 8. To 500 g of the neutralized solution (50% solid content), 2.5 g of Lumiten l-SC solution, 0.5 g of Foamaster MO 2190 and 8.3 g of Disponil FEP were added. The resulted mixture was stirred for 30 min at a speed of 500 rpm.

PSA 3

Appropriate amount of ammonia solution (20 wt%) was added to emulsion 1 as prepared above to neutralize the pH to 8. To 500 g of the neutralized solution (50% solid content), 2.5 g of Lumiten l-SC solution, 0.5 g of Foamaster MO 2190 and 25.4 g of RS 610 were added. The resulted mixture was stirred for 30 min at a speed of 500 rpm.

PSA 4

Appropriate amount of ammonia solution (20 wt%) was added to emulsion 1 as prepared above to neutralize the pH to 8. To 500 g of the neutralized solution (50% solid content), 2.5 g of Lumiten l-SC solution, 0.5 g of Foamaster MO 2190 and 38.5 g of RS 610 were added. The resulted mixture was stirred for 30 min at a speed of 500 rpm.

PSA 5

Appropriate amount of ammonia solution (20 wt%) was added to emulsion 2 as prepared above to neutralize the pH to 8. To 500 g of the neutralized solution (50% solid content), 2.5 g of Lumiten l-SC solution and 0.5 g of Foamaster MO 2190 were added. The resulted mixture was stirred for 30 min at a speed of 500 rpm.

PSA 6

Appropriate amount of ammonia solution (20 wt%) was added to emulsion 3 as prepared above to neutralize the pH to 8. To 500 g of the neutralized solution (50% solid content), 2.5 g of Lumiten l-SC solution, 0.5 g of Foamaster MO 2190 and 15.5 g of RS 610 were added. The resulted mixture was stirred for 30 min at a speed of 500 rpm.

PSA 7

Appropriate amount of ammonia solution (20 wt%) was added to emulsion 4 as prepared above to neutralize the pH to 8. To 500 g of the neutralized solution (50% solid content), 2.5 g of Lumiten l-SC solution, 0.5 g of Foamaster MO 2190 and 15.5 g of RS 610 were added. The resulted mixture was stirred for 30 min at a speed of 500 rpm.

PSA 8

Appropriate amount of ammonia solution (20 wt%) was added to emulsion 5 as prepared above to neutralize the pH to 8. To 500 g of the neutralized solution (50% solid content), 2.5 g of Lumiten l-SC solution, 0.5 g of Foamaster MO 2190 and 15.5 g of RS 610 were added. The resulted mixture was stirred for 30 min at a speed of 500 rpm.

PSA 9

Appropriate amount of ammonia solution (20 wt%) was added to emulsion 6 as prepared above to neutralize the pH to 8. To 500 g of the neutralized solution (50% solid content), 2.5 g of Lumiten l-SC solution, 0.5 g of Foamaster MO 2190 and 15.5 g of RS 610 were added. The resulted mixture was stirred for 30 min at a speed of 500 rpm.

PSA 10

Appropriate amount of ammonia solution (20 wt%) was added to emulsion 7 as prepared above to neutralize the pH to 8. To 500 g of the neutralized solution (50% S.C.), 2.5 g of Lumiten l-SC solution, 0.5 g of Foamaster MO 2190 and 15.5 g of RS 610 were added. The resulted mixture was stirred for 30 min at a speed of 500 rpm.

PSA 11

Appropriate amount of ammonia solution (20 wt%) was added to emulsion 8 as prepared above to neutralize the pH to 8. To 500 g of the neutralized solution (50% S.C.), 2.5 g of Lumiten l-SC solution, 0.5 g of Foamaster MO 2190 and 15.5 g of RS 610 were added. The resulted mixture was stirred for 30 min at a speed of 500 rpm.

PSA 12

Appropriate amount of ammonia solution (20 wt%) was added to emulsion 1 as prepared above to neutralize the pH to 8. To 500 g of the neutralized solution (50% solid content), 2.5 g of Lumiten l-SC solution and 0.5 g of Foamaster MO 2190. The resulted mixture was stirred for 30 min at a speed of 500 rpm.

Test Method

Polymer Emulsion Viscosities

The polymer emulsion viscosities have been measured according to DIN EN ISO 2555 by using a Brookfield viscometer RVT, at 23 °C and 20 rpm, using a #2 spindle.

Particle size characterization

The weight average particle diameter herein is that determined by CHDF using a Matec model-2000 CHDF measurement system with a C-202 cartridge and GR-500 (2X) eluant (diluted 1/20). The CHDF instrument was calibrated with nominal 50, 100, 200, 300, 400, 500, 600, and 700 nm polystyrene column standards ("Nanosphere"™ standards from Duke Scientific Corp., Palo Alto, Calif., USA) using the "new sigmoid fit" procedure (Matec CHDF-2000 software, version 3.20). Particle sizes were calculated using the deconvolution calculation for maximum resolution. Loop Tack, Peel and Anchorage Test

The PSAs were coated with a coat weight of 15 g/m² onto 80g art paper as carrier, and dried at 90 °C for 3 minutes. The PSA-coated carrier was slit to give test strips 25 m wide.

The loop tack test was performed according to FI NAT FTM 9.

The investigation takes place under ambient conditions: 23 ±2 °C, 50 ±5% relative humidity. Hold the two ends of the adhesive coated facing material strip and form the strip into a loop, adhesive surface outermost, by bringing the two ends together. Clamp the ends of the loop for a distance of 10mm into the top jaw of the tester leaving the loop hanging vertically downwards. The sides of the jaw should be protected from the adhesive coating. Clamp the stainless steel plate (from Chem Instruments) in the lower jaw. Position the loop into contact with the stainless steel plate at a speed of 300 mm per minute. When full contact over the stainless steel has been achieved (33mm x 25mm) immediately reverse the direction of the machine and allow separation to take place at a speed of 300 mm per minute. Record the maximum force necessary to completely separate each loop from the stainless steel plate. The strips should be 25mm wide and have a minimum length of 175mm in the machine direction.

The peel test was performed according to FINAT FTM 2 (90° peel test).

A stainless-steel test panel (Chem Instruments, at least 3 cm * 25 cm) is used as the substrate on which the test strip is applied. The test strip is rolled twice with 2 kg FINAT test roller to firmly bond it to test panel. Fix the test panel and test strip into the horizontal support which is secured in the bottom jaw of the tester. Set the machine at 300mm per minute jaw separation rate, set the motor to move the test panel horizontally and keep the test angle between strip and panel to be 90 °. Set the machine load averaging function to average data. Peel adhesion (90°) is the average result for the strips tested in Newtons per 25mm width.

All specimens are tested after laminated 20 minutes (noted as "Before Aging, (BA)") and after aging at 70 °C for 7 days (noted as "After Aging, (AA)"), respectively.

The anchorage test was performed according to internal standard.

The investigation takes place under ambient conditions: 23 ±2 °C, 50 ±5% relative humidity. Rub the adhesive layer of a test strip 3 times by finger with constant force and record the area percent of the residue adhesive on the test strip, wherein two individual measurements are carried out for each sample. Assign an anchorage rating according to the following criteria:

Anchorage rating 1: less than 50% of the area on test strip has adhesive residue. Anchorage rating 2: more than 50% and less than 95% of the area on test strip has adhesive residue.

Anchorage rating 3: more than 95% of the area on test strip has adhesive residue.

For each PSA formulation, two independent tests were performed, and an average rating was adopted.

Table 1

Particle- , Peel

Loop - size Surfactant Anchorage

Tack BA* AA**

Distribution PSA 1 Multimodal 2 wt% RS 610 3 3.0 2.2 3.0

0.8 wt%

PSA 2 Multimodal

1.8 2.6 3.5 Disponil FEP

3.3 wt% RS

PSA 3 Multimodal 3 3.8 2.6 3.3

610

PSA 4 Multimodal 5 wt% RS 610 2.5 3.3 2.5 3.7 PSA 5 Multimodal 2 wt% RS 610 3 2.2 1.2 5.0 PSA 6 Multimodal 2 wt% RS 610 2.5 2.0 0.7 4.8 PSA 7 Multimodal 2 wt% RS 610 3 3.0 3.7 3.2 PSA 8 Multimodal 2 wt% RS 610 2.5 3.0 4.6 4.9 PSA 9 Bimodal 2 wt% RS 610 3 3.3 2.7 3.3 PSA

Monomodal 2 wt% RS 610 3 4.3 2.0 6.5 10 PSA

Monomodal 2 wt% RS 610 2.5 4.4 2.0 6.2 11

PSA No phosphate

Multimodal

4.7 3.2 4.7

12 Surfactant

*BA: Before Aging

**AA: After Aging

The anchorage performance of all the PSAs meet the application requirement. However, it is surprising that the peel strength after aging of PSAs with multimodal particle size distribution can be maintained at reasonably low level. The peel strength after aging for PSAs with multimodal particle size distribution is no higher than 5 Newtons. Lower peel strength after aging means easy removal. This is beneficial for adhesive articles that have to survive aging conditions and be removed afterwards. Therefore, it is suitable for applications as removable adhesive. In contrast, peel strength after aging for PSAs with monomodal size distribution show significantly higher peel strength after aging.

More interestingly, the addition of phosphate surfactants into PSAs with multimodal particle size distribution can further improve the loop tack performance of the PSAs. The loop tack value of a PSA is the force required to separate, at a specified speed, a loop of material (adhesive outermost) which has been brought into contact with a specified area of a standard surface. The loop tack shall not be too high for many applications.

Additional peel test for PSA 1 and PSA 9 on different substrates

The PSAs were coated with a coat weight of 15 g/m² onto 70g thermal paper as carrier, and dried at 70 °C for 7 days. The PSA-coated carrier was slit to give test strips 25 mm wide. The peel test was performed according to FI NAT FTM 2 (90° peel test). A PC test panel (from BASF, at least 3 cm * 25 cm) or an ABS test panel (from BASF, at least 3 cm * 25 cm) is used as the substrate on which the test strip is applied. The test strip is rolled twice with 2 kg FI NAT test roller to firmly bond it to test panel. Fix the test panel and test strip into the horizontal support which is secured in the bottom jaw of the tester. Set the machine at 300mm per minute jaw separation rate, set the motor to move the test panel horizontally and keep the test angle between strip and panel to be 90°. Record the percentage of adhesive transferred to the PC or ABS panel and the data is listed in Table 2.

Table 2

The adhesive of PSA 9 does not transfer to the panel, whether it’s PC panel or ABS panel, while PSA 1 shows obvious adhesive transfer when applied onto PC panel and ABS panel.

Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It will be apparent to those skilled in the art that various modifications and variations can be made to the method and apparatus of the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention include modifications and variations that are within the scope of the appended claims and their equivalents.

Claims

CLAIMS:

1. A water-borne polymer composition comprises

Wherein the composition has a bimodal or multimodal particle-size distribution.

2. A water-borne polymer composition according to claim 1 , wherein hydrophobic ethylenically unsaturated monomer accounts for, based on the total weight of the polymer, at least 85 wt%, preferably at least 90 wt%, more preferably at least 95% by weight and the hydrophilic ethylenically unsaturated monomer accounts for, based on the total weight of the polymer, at least 0.2 wt% and no more than 15 wt%, preferably at least 0.5 wt% and no more than 10 wt%, and more preferably at least 1 wt% and no more than 5 wt%.

3. A water-borne polymer composition according to claim 1 or 2, wherein the hydrophobic ethylenically unsaturated monomer is chosen from methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate, styrene or a mixture thereof and the hydrophilic ethylenically unsaturated monomer is chosen from acrylic acid, methacrylic acid, itaconic acid, acrylamide, methacrylamide or a mixture thereof.

4. A water-borne polymer composition according to any of the proceeding claims, wherein the polymer has an overall Fox Tg in the range of -15 to -65 °C, preferably -20 to -60 °C and more preferably -25 to -55 °C.

5. A water-borne polymer composition according to any of the proceeding claim, wherein at least 40%, preferably at least 45%, more preferably at least 50%, by weight, of the polymer particles have a weight average particle diameter in the range of 400 to 1,000 nm, preferably in the range of 450 to 900 nm and more preferably in the range of 480 to 800 nm while no more than 60%, preferably no more than 55% and more preferably no more than 50%, by weight, of the polymer particles have a weight average particle diameter in the range of 80 to 550 nm, preferably in the range of 100 to 500 nm and more preferably in the range of 120 to 480 nm.

6. A water-borne polymer composition according to claim 5, wherein at least 40%, by weight, of the polymer particles have a weight average particle diameter in the range of 400 to 1 ,000 nm and no more than 60%, by weight, of the polymer particles have a weight average particle diameter in the range of 80 to 550 nm; preferably at least 45%, by weight, of the polymer particles have a weight average particle diameter in the range of 450 to 900 nm and no more than 55%, by weight, of the polymer particles have a weight average particle diameter in the range of 100 to 500 nm; and more preferably at least 50%, by weight, of the polymer particles have a weight average particle diameter in the range of 480 to 800 nm and no more than 50%, by weight, of the polymer particles have a weight average particle diameter in the range of 120 to 480 nm.

7. A water-borne polymer composition according to any of the proceeding claims, wherein the composition further comprises at least one emulsifier selected from compounds of the formula (I), (II) or a mixture thereof:

[R¹0(A0)_m][R²0(A0)_n]P(=0)(0M¹) (I)

R (AO)_mP(=0)(OM¹)(OM²) (II)

8. A water-borne polymer composition according claim 7, wherein R¹ and R² are independently linear/branched/cyclic C8-C25 alkyls, benzene or its derivatives, more preferably linear/branched/cyclic C₈-C₂₀ alkyls, C₄-C₈ alkyl benzyl, C₄-C₁₀ alkyl benzoate/aryloxy; m and n are independently an integer from 1 to 15, more preferably 1 to 10 and most preferably 1 to 6; AO is chosen from (- CH₂CH₂O-), (-CH₂CH₂CH₂O-) and (-CH₂(CH₃)CHO-); and M¹ and M² are independently a H or Na⁺ or K⁺.

9. A water-borne polymer composition according claim 7 or 8, wherein the surfactant of formula (I) or formula (II) or in combination may be added in an amount of, based on the total weight of the water-borne polymer composition, 0.2-10 wt%, preferably 0.5-8 wt%, more preferably 1-5 wt% and most preferably 1.5-4 wt%.

10. A water-borne polymer composition according claim 7, 8 or 9, wherein the composition further comprises other surfactant besides the surfactant of formula (I) or formula (II) or in combination.

11. A water-borne polymer composition according claim 10, wherein the other surfactant is at least one polymerizable surfactant.

12. A method for making the water-borne polymer composition according to any of the proceeding claim, wherein the method includes mixing the surfactant of formula (I) or formula (II) or in combination during the polymerization or afterwards.

13. Use of the water-borne polymer composition according to any of the proceeding claim as removable pressure sensitive adhesive.