CA1268581A - Pressure sensitive adhesives - Google Patents

Pressure sensitive adhesives

Info

Publication number
CA1268581A
CA1268581A CA000478417A CA478417A CA1268581A CA 1268581 A CA1268581 A CA 1268581A CA 000478417 A CA000478417 A CA 000478417A CA 478417 A CA478417 A CA 478417A CA 1268581 A CA1268581 A CA 1268581A
Authority
CA
Canada
Prior art keywords
weight
monomer
sheet material
coating
composition according
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA000478417A
Other languages
French (fr)
Inventor
John B. Clarke
John F. Firth
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ciba Specialty Chemicals Water Treatments Ltd
Original Assignee
Allied Colloids Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Allied Colloids Ltd filed Critical Allied Colloids Ltd
Application granted granted Critical
Publication of CA1268581A publication Critical patent/CA1268581A/en
Expired legal-status Critical Current

Links

Landscapes

  • Adhesive Tapes (AREA)
  • Adhesives Or Adhesive Processes (AREA)

Abstract

ABSTRACT
PRESSURE SENSITIVE ADHESIVES
A pressure sensitive adhesive, that is particularly suitable for use as the adhesive on labels for frozen food packages, is an emulsion of polymer particles formed from tackifying monomer, optionally diluent monomer, and a small amount of acrylic acid or other hydrophilic monomer, the polymer being linear and having a second order transition temperature of less than -25°C.

Description

1~6~35~

PRESSURE SENSITIVE ADH~SIVES __ It is known to formulate pressure sensitive adhesive compositions from polymers of 2-ethyl hexyl acrylate or other medium chain length alkyl acrylates or methacrylates, optionally with other acrylate esters such as butyl acrylate or methyl methacrylate. The polymers are generally made by solution polymerisation but can be made by emulsion polymerisation. They are often cross-linked.
For various purposes it is known to include other monomers, including hydrophilic monomers, in the polymerisable mixture.
In DE 301B131 a copolymer of 2-ethylhexyl acrylate with other monomers including hydroxypropyl acrylate is formed and, before casting, is cross-linked by reaction with isocyanate. The final polymer is therefore free of hydroxypropyl groups. In JP 57031972 a copolymer of
2-ethylhexyl acrylate, methyl methacrylate, acrylic acid and itaconic acid is cross-linked by ethylene dimethacrylate during emulsion polymerisation, to give a releasable adhesive. In JP 57070162 a copolymer of 2-ethylhexyl acrylate, methacrylic acid and N-methylol acrylamide is formed by polymerisation in an emulsion in water in the presence of an amphoteric surfactant. The product emulsion is neutralised with ammonia before being cast onto labels and this neutralisation will result in cross-linking between methylol acrylamide groups after casting. These cross-linked polymers will form co~erent films that are relatively hard and that do not flow or adhere very well at low temperatures.
In GB 2070631 a pressure sensitive adhesive suitable for application to skin is formed by solution polymerisation of up to 62~ butyl acrylate, 4 to 10 acrylic acid and 34 to ~0~ 2-ethylhexyl acrylate.

358~

In US 3515630 a composition containing starch, plasticiser and a vinyl acetate copolymer with ethylhexyl acrylate and 0 to 5% by weight acid such as acrylic acid or itaconic acid is described. The presence of the plasticiser is undesirable as this is likely to migrate from the composition.
In US 3691140 polymer particles that can be sprayed to form an adhesive coating are described as being made by suspension polymerisation of 2-ethylhexyl acrylate in the presence of oil soluble initiator, emulsifier, and water soluble ionic monomer. Amongst the water soluble monomers that are mentioned are ammonium acrylate and sodium acrylate. The particle size obtainable is relatively high, for instance 6 to 52 microns in the example using ammonium acrylate. The aqueous dispersion obtained by the polymerisation is unstable and separates into two phases. Although it is mentioned that the aqueous dispersion can be used immediately to provide a coating in the preferred method the polymer particles are coagulated from the unstable dispersion, dried and resuspended in organic solvent ready for being sprayed as an aerosol.
Pressure sensitive adhesive compositions are often provided in an organic solvent but compositions in which the adhesive is emulsified or dispersed in water are also known. Compositions based on organic solvents have a number of disadvantages, particularly when they are to be used as the adhesive on a price label, especially for frozen food packages. Solvent based compositions~incur the inevitable inconvenience and disadvantages associated with the use of organic solvents, including the toxicity problems associated with them. Also existing compositions are liable to strike through the label during drying and so in practice either have to be applied by a transfer process (with the composition being 858~L

dried whilst supported on a transfer sheet) or the label has ~o be given a primer coat ~efore the adhesive is applied.
It would therefore be desirable to be able to provide a water based pressure sensitive adhesive suitable for use on frozen food packages. For such packages the adhesive must be capable of being handled at room temperature and yet it must be adherent to surfaces having temperatures as low as -30C and having a layer of water or ice on them. For instance frozen food packages are often price labelled when they have a layer of condensation on their surfaces.
A pressure sensitive adhesive composition according to the invention comprises a stable aqueous emulsion of polymer particles having a particle size at least 90% by weight below 2 microns and which are of a linear copolymer formed from 90 to 99.5% by weight tackifying monomer selected from C2 18 alkyl acrylates and C6 10 alkyl methacrylates, 0 to 5% by weight diluent monomer and 0.5 to 5% by weight hydrophilic monomer selected from carboxylic and sulphonic ethylenically unsaturated monomers that are substantially insoluble in the tackifying monomer and the polymer has a second order transition temperature of less than -25C. It can be as low as, for i~stance, -75C.
A method according to the invention for making a pressure sensitive adhesive composition comprises emulsion polymerisation of polymerisable monomers in an aqueous medium containing an emulsifier and ~under conditions such that the final particle size of the emulsion polymer is at least 90~ by weight below 2 microns, and in which the monomers consist of from 90 to 99.5% hy weight tackifying monomer selected from C2 18 alkyl acrylates and C6 10 alkyl methacrylates, 0 to 5~ by weight diluent monomer and 0.5 to 5% by weight 6~

hydrophilic monomer selected from carboxylic and sulphonic eth~lenically unsaturated monomers that are substantially insoluble in the tackifying monomer and are selected such that the final polymer is linear and has a second order transition temperature of less than -25C.
A sheet material according to the invention comprises a paper or other flexible substrate carrying a coating formed by casting such an emulsion and drying the coating. This sheet material can, for instance, be a label. The coating will adhere well to frozen goods both during storage and when applied to frozen goods, even when they are covered with a film of condensation.
It is important to select the hydrophilic monomer that it is substantially insoluble in the tackifying monomers since this promotes the migration of the hydrophilic monomer to the surface of the emulsion particles. For instance methacrylic acid is unsatisfactory since it tends to distribute throughout the hydrophobic monomer and so monomers having lower solubility in oil than methacrylic acid should be used.
These monomers include itaconic acid, 2-acrylamido-2-methyl propane sulphonic acid and, preferably, acrylic acid. The polymerisation may be conducted whilst the monomers are in the free acid form or neutralised with ammonia or alkali metal.
Preferably the hydrophilic monomer is acrylic acid present in an amount of from 0.5 to 4~, generally 1 to
3%. The higher amounts, eg above 2%, promote permanent adhesion to the frozen package whilst lower amounts, eg below 24, tend to provide a peelable adhesive.
The polymer is yenerally formed solely from the tackifying monomer and hydrophilic monomer but a small amount of methyl methacrylate or other diluent monomer may be included provided this does not undesirably increase the glass transition temperature of the polymer.

~ 85~3~

The tackifying monomer is generally selected from C6_12 alkyl acrylates. Usually at least 50~, normally at least 75% and preferably all the tackifying monomer is 2-ethylhexyl acrylate. Thus preferred polymers consist of 0.5 to 4% by weight acrylic acid and 96 to 99.5% by weight 2-ethylhexyl acrylate. Such polymers have second order transition temperatures of about -40 to ~60C. If other monomers are present they are preferably such that the second order transition temperature is not more than -40C.
The emulsion polymerisation must be conducted under conditions such that the particle size o~ the emulsion is at least 90% by weight below 2 microns, preferably at least 90% by weight, most preferably 99~ by weight, below 1 micron, for instance 0.1 to 1 micron. The desired particle size may be achieved in known manner, for instance by appropriate choice of emulsifier, amount, and agitation. The emulsifier is preferably a non-ionic or anionic surfactant, for instance a sulphonated nonylphenol ethylene oxide surfactant~
The polymerisation is preferably initiated using a water soluble thermal or other initiator, such as ammonium persulphate. The emulsion is usually free of additives other than emulsifier and initiator. The polymerisation is normally permitted to go to completion without any deliberate steps being taken to terminate it.
An advantage of emulsion polymerisation in this manner is that the polymer has a high molecular weight.
Preferably the molecular weiyht is as high as possible, the polymer preferably having an intrinsic viscosity greater than 3.
The polymerisation may be conducted under basic conditions, while the carboxylic or sulphonic groups are present as alkali metal or ammonium salts, but preferably the polymerisation is conducted under acidic conditions ~2~i~5~

and the final emulsion is then neutralised by adding, for instance, sodium hydroxide or ammonia, generally in an amount to neutralise all the acid groups.
The emulsion must be stable, and this will generally follow automatically from the particle size and the choice of surfactant but if necessary additional emulsion stabiliser, either surfactant or thickener, may be added if desired. Generally this is unnecessary.
The emulsion can be coated onto the paper or other substrate and dried to form the pressure sensitive coating, all in conventional manner. Thus coating may be direct onto the substrate or indirect, onto a release paper onto which the substrate is then applied. The dry weight of the coating is generally from lO to 30 g/m2.
To test adhesive properties, between 20-22 g/m2 of dry adhesive is coated on kraft paper of the type used to manufacture labelstock and the peel strength, shear strength and tack are measure* as follows.
PEEL STRENGTH
A strip of coated paper, 2.54 cm wide, is bonded to a glass plate by applying a constant pressure. An Instron~testing machine is then used to measure the force required to peel the paper strip, at an angle of 180, at a rate of 300 mm/minute at 20C.
SHEAR STRENGTH
A strip of coated paper is fixed to the edge of a glass plate, so that an area of 6.45 square cm (1 square inch) is in contact with the glass. The force required to remove the strip at an angle of 2 is measured at 1.0 mm/minute and 20C.
TACK
A loop formed from a 2.54 cm strip of coated paper is lowered by an Instron~machine onto a glass plate. The force required to remove the tape is measured at a rate of 300 mm/minute at 20C.

r~J~ k s~

The polymer should be formulated such that tack strength is at leas-t 5 Newtons and generally at least 8, for instance up to 10 or more Newtons, shear strength is at least 55 Newtons, preferably at least 90 Newtons and may be up to 110 Newtons or more and peel strength is at least 5 Newtons, preferably at least 9 Newtons and may be up to 12 Newtons or more.
Suitabili~y for application to frozen packages can be determined merely by coating paper with the emulsion, drying the coating and then applying the coated surface onto a polythene bag filled with ice and that has recently been removed from the refrigerator.
The following is an example of the invention.
495 g 2-ethylhexyl acrylate, 5 g glacial acrylic acid and chain transfer agent were pre-emulsified in about 250 parts aqueous phase containing 10% sodium alkyl nonyl ether sulphate as emulsifier and containing sequestrant and ammonium persulphate initiator. The resultant emulsion was fed over a period of 2 to 3 hours into about 250 g aqueous phase containing about 1~
emulsifier, together with sequestrant and initiator, at about 80C. Polymerisation was allowed to proceed and then terminated. The mixture was cooled to give an emulsion containing 50% polymer. The emulsion was discharged from the reaction vessel and could be coated onto paper as such, or after adding rheology adhesives.
A label coated with the emulsion adhered satisfactorily to a frozen package but could be removed by peeling.
If it is desired for the label to be non-removable then the process can be repeated using 15 g glacial acrylic acid instead of 5 g.

Claims (8)

1. A pressure sensitive adhesive composition comprising a stable aqueous emulsion of polymer particles having a particle size at least 90% by weight below 2 microns and which are of a linear copolymer formed from 90 to 99.5%
by weight tackifying monomer selected from C2-18 alkyl acrylates and C6-10 alkyl methacrylates, 0 to 5% by weight diluent monomer and 0.5 to 5% by weight hydrophilic monomer selected from carboxylic and sulphonic ethylenically unsaturated monomers that are substantially insoluble in the tackifying monomer and the polymer has a second order transition temperature of less than -25°C.
2. A composition according to claim 1 in which the hydrophilic monomer is acrylic acid and is present in an amount of from 0.5 to 4, by weight of the monomers.
3. A composition according to claim 1 in which the tackifying monomer is selected from C6-12 alkyl acrylates and at least 75% by weight of the tackifying monomer is 2-ethylhexyl acrylate.
4. A composition according to claim 1 in which the polymer is formed from 0.5 to 4% by weight acrylic acid and 96 to 99.5% by weight 2-ethylhexyl acrylate.
5. A process of coating sheet material which comprises coating onto the sheet material a stable aqueous emulsion of polymer particles as defined in claim 1, and drying the aqueous emulsion coating on the sheet material.
6. A process of coating sheet material which comprises coating onto the sheet material a stable aqueous emulsion of polymer particles as defined in claim 2, claim 3 or claim 4, and drying the aqueous emulsion coating on the sheet material.
7. A frozen food package carrying a label bonded to the package using an adhesive layer obtained by casting and drying a composition according to claim 1.
8. A frozen food package carrying a label bonded to the package using an adhesive layer obtained by casting and drying a composition according to any of claims 2, 3 or 4.
CA000478417A 1984-12-11 1985-04-04 Pressure sensitive adhesives Expired CA1268581A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB848431168A GB8431168D0 (en) 1984-12-11 1984-12-11 Pressure sensitive adhesives
GB8431168 1984-12-11

Publications (1)

Publication Number Publication Date
CA1268581A true CA1268581A (en) 1990-05-01

Family

ID=10570975

Family Applications (1)

Application Number Title Priority Date Filing Date
CA000478417A Expired CA1268581A (en) 1984-12-11 1985-04-04 Pressure sensitive adhesives

Country Status (2)

Country Link
CA (1) CA1268581A (en)
GB (1) GB8431168D0 (en)

Also Published As

Publication number Publication date
GB8431168D0 (en) 1985-01-23

Similar Documents

Publication Publication Date Title
US4925908A (en) Acrylic based emulsion polymers
KR100197315B1 (en) Positionable adhesive system with high shear strength
EP0797644B1 (en) Removable pressure sensitive adhesive and article
US3690937A (en) Process of making a pressure-sensitive adhesive material
US5817426A (en) Acrylic pressure-sensitive adhesives for low-energy surfaces and corrugated board
EP0596642B1 (en) Aqueous release coating composition
US5073457A (en) Repositionable adhesive
EP0794864B1 (en) Cold sealable coating
US5240989A (en) Removable pressure-sensitive adhesive compositions comprising acrylic based emulsion polymers
US6080480A (en) Delayed-tack adhesive composition
KR20040069205A (en) Synthetic resin emulsion, easily water-swellable pressure-sensitive adhesive compositions containing the same and process for production of the emulsion
US6337360B1 (en) Method of producing aqueous dispersions as a base for hot sealing adhesives
JP2003313525A (en) Water dispersion-type adhesive composition and adhesive product
JPH0229407A (en) Dispersion of non-tertiary butyl(meth)acrylate copolymer having glass transition temperature of -10 degree or less
US4753846A (en) Adhesive compositions for use on vinyl substrates
EP0147067A1 (en) Pressure sensitive adhesives
US4812547A (en) Pressure sensitive adhesives comprising ethylene vinyl acetate dioctyl maleate terpolymers
CA1268581A (en) Pressure sensitive adhesives
US4892917A (en) Adhesive compositions for use on vinyl substrates
EP0401226B1 (en) Removable pressure-sensitive adhesive compositions comprising acrylic based emulsion polymers
EP1447434A1 (en) Aqueous dispersion type pressure-sensitive adhesive composition and pressure-sensitive adhesive product
US4826938A (en) Substrates coated with pressure sensitive adhesives comprising ethylene vinyl acetate dioctyl maleate polymers
KR100550259B1 (en) Acrylic Emulsion Pressure Sensitive Adhesive Showing Excellent Water-resistance and Low Time-dependency
JPS5814471B2 (en) Removable adhesive composition
US5089335A (en) Crosslinking primer for flexible packaging film

Legal Events

Date Code Title Description
MKLA Lapsed