Washoff pressure sensitive adhesive for PET

Abstract

A pressure sensitive adhesive (PSA) that can be washed off from a substrate is disclosed. The PSA may include at least one hydrophilic monomer, at least one hydrophobic monomer, at least one neutralizing agent, and at least one surfactant. A label having a base layer coated with an acrylic binder and a PSA layer, wherein the PSA layer comprises at least one hydrophilic monomer, at least one hydrophobic monomer, at least one neutralizing agent, and at least one surfactant.

Description

Technical Field

[0001] The present disclosure relates to pressure sensitive adhesives (PSAs) that are washed off from various substrates. More specifically, the present disclosure relates to a pressure sensitive adhesive layer comprising at least one hydrophilic monomer, at least one hydrophobic monomer, at least one neutralizing agent, and at least one surfactant. Background Art

[0002] Adhesive compositions can be used for a wide variety of purposes. A particularly useful subset of adhesive compositions is water-based pressure sensitive adhesives. The use of water-based pressure sensitive adhesives in different end-use applications is generally known. For example, water-based pressure sensitive adhesives can be used with labels, notepads, tapes, decals, bandages, decorative and protective sheets, and many other products.

[0003] As used in the art, the term "pressure-sensitive adhesive" refers to a material comprising one or more polymer compositions that, when dry, is strongly tacky and permanently tacky at various temperatures. Further, the term "water-based" means that the pressure-sensitive adhesive is made with an aqueous carrier. Typical water-based pressure-sensitive adhesives will adhere firmly to a variety of different surfaces upon mere contact, without requiring more pressure from fingers or hands.

[0004] Pressure sensitive adhesives are commonly used to adhere paper or film labels to PET. PET is often recyclable, but usually only if the PSA can be easily removed. Crushing a PET container with a PSA label still attached can cause processing challenges and contamination. Currently temperatures of 80°C or higher are necessary to remove labels from substrates. Labels and adhesives that can be cleanly removed from substrates such as PET without excessive heat would allow the container to be reused with minimal post-processing. Therefore, PSA-based labels that can be easily washed off at lower temperatures are desirable. DETAILED DESCRIPTION

[0005] The present disclosure relates to a pressure sensitive adhesive (PSA) that can be washed off a substrate. More specifically, the PSA layer comprises at least one hydrophilic monomer, at least one hydrophobic monomer, at least one neutralizing agent, and at least one surfactant.

[0006] A label having a substrate layer coated with a hydrophilic or hydrophobic acrylic adhesive and a PSA layer is currently disclosed, wherein the PSA layer comprises at least one hydrophilic monomer, at least one hydrophobic monomer, at least one neutralizing agent and at least one surfactant. Optionally, treated with an acrylic adhesive having a Tg greater than 5°C.

[0007] According to the present disclosure, a constantly stirred bath having a temperature below 85 degrees Celsius and a pH between 7 and 14 may be used to remove PSA.

[0008] Basal layer

[0009] The presently disclosed substrate layer for forming a wash-off label may comprise a single layer of substrate material or may be formed of a multilayer construction. The properties of the material used to form the substrate layer as well as the intended use and desired performance properties of the label may determine the selection of an appropriate material and construction for the substrate layer. In the case of a multilayer substrate, an important consideration is the nature of the outer layer in contact with the PSA layer.

[0010] In a multilayer substrate, it may be advantageous for one or more of the layers other than the layers in contact with the PSA to be a stressed substrate, such as uniaxially or biaxially stretched polyvinyl chloride or other stretchable substrate which, when subjected to appropriate wash-off conditions, will curl and aid in pulling the label away from the glass or plastic substrate.

[0011] A variety of materials can be used to form the substrate layer, including paper and polymer compositions. The material can be primed or unprimed. The material can be shrinkable / expandable or non-shrinkable. The material can be surface treated by, for example, corona discharge, flame, plasma, etc., to provide a surface with desired properties, such as increased adhesion to subsequently applied layers. The procedures for corona treatment and flame treatment of polymer substrates are well known to those skilled in the art.

[0012] The substrate layer can be a single layer substrate or a multilayer substrate. The multilayer substrate can include two or more layers. The substrate layer can be oriented or non-oriented. The substrate layer can be transparent or opaque.

[0013] Suitable polymers for preparing the substrate layer may include, for example, polymers and copolymers of one or more of the following: polyolefins, polyacrylates, polystyrenes, polyamides, polyvinyl alcohols, poly(alkylene acrylates), poly(ethylene vinyl alcohols), poly(alkylene vinyl acetates), polyurethanes, polyacrylonitrile, polyesters, polyester copolymers, fluoropolymers, polysulfones, polycarbonates, styrene-maleic anhydride copolymers, styrene-acrylonitrile copolymers, ionomers based on sodium or zinc salts of ethylene methacrylic acid, polyacrylonitrile, alkylene-vinyl acetate copolymers, or so-called "biopolymers", or mixtures of two or more of the above. The substrate layer may include a polyamide film, such as polyamide 6, polyamide 11, and polyamide 12.

[0014] As presently disclosed, the plastic substrate of the base layer can be unstressed (i.e., unstretched), or stretched in at least one direction. In a multilayer substrate, only one layer or less than all of the layers can be stretched uniaxially or biaxially. In the case of a multilayer substrate in which more than one layer is stretched, the layers can all be stretched in substantially the same orientation, or different layers can be stretched in different orientations relative to each other.

[0015] As currently disclosed, the substrate layer or at least the layer of the multilayer substrate with the adhesive layer can be treated before applying the adhesive layer, for example by corona treatment, flame pretreatment, plasma pretreatment or chemical grafting, or by means of an adhesion-promoting interlayer comprising, for example, chlorinated polyolefins, chlorinated rubbers, ethylene / vinyl acetate (EVA) copolymers, chlorinated polypropylene or polymerized ethylene / acrylamide comonomers. The substrate can also be treated with an acrylic adhesive having a Tg greater than 5°C, which can be obtained from DOW chemical. The acrylic adhesive can be applied to the substrate at a rate of 0.05 gsm to 3.0 gsm. The acrylic adhesive can be applied to PET at a rate of 0.05 gsm to 3.0 gsm.

[0016] PSA layer

[0017] A PSA layer formed by drying an aqueous polymer dispersion is disclosed. The polymer of the dispersion comprises at least one hydrophilic monomer and at least one hydrophobic monomer. The PSA also comprises at least one neutralizing agent and at least one surfactant. The PSA may have 50% to 90% hydrophobic monomers, 50% to 80% hydrophobic monomers, 50% to 70% hydrophobic monomers, or 50% to 60% hydrophobic monomers. Examples of acceptable hydrophobic monomers include, but are not limited to, alkyl acrylates such as butyl acrylate, ethylhexyl acrylate, octyl acrylate, isooctyl methacrylate, decyl methacrylate, isodecyl methacrylate, lauryl methacrylate, pentadecyl methacrylate, stearyl methacrylate, and C methacrylate. 12 To C 18 All weight percentages are based on the total weight of the adhesive composition.

[0018] The PSA may have 25% to 30% hydrophilic monomers, 26% to 30% hydrophilic monomers, 27% to 30% hydrophilic monomers, 28% to 30% hydrophilic monomers, or 29% to 30% hydrophilic monomers. Examples of acceptable hydrophilic monomers include, but are not limited to, alkyl acrylates such as ethyl acrylate, methyl acrylate, and propyl acrylate, as well as acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate.

[0019] The preparation of aqueous dispersions of water-insoluble latex polymers by emulsion polymerization is well known in the art. The practice of emulsion polymerization is described in D.C. Blackley, Emulsion Polymerization (1996). Emulsion Polymerization ) (Wiley, 1975) and in H.Warson, Applications of Synthetic Resin Latex ( The Applications of Synthetic Resin Emulsions )”, Chapter 2 (Ernest Benn Ltd., London 1972). Polymerization methods and useful polymerization aids, such as dispersants, initiators, chain transfer agents, etc. are well known and described, for example, in published U.S. patent application US2008 / 0176996.

[0020] An initiator can be introduced into a water kettle into which the emulsified monomer mixture is fed. The initiator can be configured to react with at least one monomer to form an emulsion polymer comprising monomer subunits. The initiator can react with the monomers dispersed throughout the aqueous medium until all or substantially all of the monomers are polymerized. The end result can be a dispersion of polymer particles in an aqueous medium comprising monomer subunits. Such dispersions are commonly referred to as emulsion polymers. After all monomers are fed into the emulsion polymer, additional redox initiators can be introduced into the emulsion polymer to reduce the level of residual monomers.

[0021] Reduction-oxidation (redox) initiator systems consisting of at least one, usually inorganic, reducing agent and an inorganic or organic oxidizing agent are particularly suitable. The oxidizing component may include, for example, ammonium and alkali metal salts of peroxodisulfuric acid, for example sodium peroxodisulfate, hydrogen peroxide or an organic peroxide, for example tert-butyl hydroperoxide or tert-amyl hydroperoxide. The reducing component may include, for example, alkali metal salts of sulfites, such as sodium sulfite, sodium bisulfite; alkali metal salts of disulfites, such as sodium disulfite; addition compounds of bisulfites with aliphatic aldehydes and ketones, such as acetone bisulfite; or reducing agents, such as hydroxymethanesulfinic acid and its salts, FF6 or isoascorbic acid. Redox initiator systems can be used with soluble metal compounds having a metal component that can exist in multiple valence states.

[0022] Examples of commonly used redox initiator systems are tert-butyl hydroperoxide / sodium bisulfite, tert-butyl hydroperoxide / isoascorbic acid and tert-butyl hydroperoxide / sodium hydroxymethanesulfinate. Individual components, such as the reducing component, can also be mixtures, such as a mixture of hydroxymethanesulfinic acid sodium salt and sodium disulfite.

[0023] After polymerization, the emulsion polymer dispersed throughout the aqueous medium may be stabilized by a sodium salt of a fatty alcohol ether sulfate surfactant post-additive. The sodium salt of the fatty alcohol ether sulfate surfactant may comprise at least 0.5% of the composition. The sodium salt of the fatty alcohol ether sulfate surfactant may comprise 0.5% to 3% of the composition. The sodium salt of the fatty alcohol ether sulfate surfactant may comprise 1.0% to 1.3% of the composition. The sodium salt of the fatty alcohol ether sulfate surfactant may comprise 1.0% to 3% of the composition. Examples of suitable sodium salts of fatty alcohol ether sulfate surfactants include, but are not limited to FES 77, FES 32, FES 993 and FES 61, all of which are available from BASF. Other coating additives may also be optionally added.

[0024] Dioctyl sodium sulfosuccinate ( OT-75) and acetylene glycol ethylene oxide / propylene oxide adduct surfactants can also be added to the composition. Dioctyl sodium sulfosuccinate can account for 0.1% to 3.0% of the composition. Dioctyl sodium sulfosuccinate can account for 0.2% to 0.5% of the composition. Dioctyl sodium sulfosuccinate can account for 0.2% to 1.5% of the composition. Alkyne glycol ethylene oxide / propylene oxide adduct surfactants can account for 0.05% to 1.5% of the composition. Alkyne glycol ethylene oxide / propylene oxide adduct surfactants can account for 0.1% to 0.5% of the composition. Acceptable acetylene glycol ethylene oxide / propylene oxide adduct surfactants include but are not limited to 440, 104. 420, 450, 465 and 485. OT-75 is available from Solvay, and Surfactants are available from Evonik. The acetylenic diol ethylene oxide / propylene oxide adduct surfactants may be replaced or combined with nonionic branched secondary alcohol ethoxylate surfactants.

[0025] Optionally, water-soluble additives that improve wash-off performance can be used in combination with the polymer backbone. The example of water-soluble additives is a synthetic water-soluble polymer such as polyethylene glycol (PEG), polyvinyl pyrrolidone (PVP), poly (vinyl alcohol) (PVOH), polyacrylic acid (PAA), polyacrylamide, N-(2-hydroxypropyl) methacrylamide (HPMA), divinyl ether-maleic anhydride (DIVEMA), polyoxazoline, polyphosphate, polyphosphazene, natural water-soluble polymers such as xanthan gum, pectin, chitosan derivatives, dextran, carrageenan, guar gum, cellulose ether, hyaluronic acid (HA), albumin, starch or based on starch derivatives or their combination. During the wash-off label in the washing station, the water solubility and hydrophilicity of polymers such as polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) allow adhesive to contact with the washing liquid relatively quickly and fully, making it convenient for the washing liquid to penetrate behind the label, and realizing the wash-off of the label in the predetermined washing time of about a few minutes. Examples of water-soluble additives include PEG 400, PEG 600, PEG 1000, PEG 1450, PEG 3350, PEG 8000, PVP K60, PVP K90 with different molecular weights. The concentration and molecular weight of the water-soluble additive need to balance the wash-off performance, adhesive (PSA) properties, viscosity, clarity of the dry adhesive, stability of the emulsion, solids %, rheology and coatability of the final product formulation. For example, the concentration of the active water-soluble additive can range from 0.05% to 20%. Preferably 0.25% to 10%.

[0026] The presently disclosed PSAs do not contain effective amounts of any crosslinking component, do not contain effective amounts of any tackifier or other additive. The presently disclosed PSAs do not contain effective amounts of adipic acid dihydrazide (ADH) or waxes. The presently disclosed PSAs do not contain effective amounts of polyhydroxy functional amines. The presently disclosed PSAs do not contain effective amounts of photocrosslinkable monomers. The presently disclosed PSAs also do not contain effective amounts of vinyl acetate or vinyl acetate derivatives.

[0027] A label is currently disclosed, the label comprising a substrate layer and a pressure-sensitive adhesive layer, wherein a hydrophilic or hydrophobic acrylic adhesive is optionally applied to the adhesive side of the substrate layer, and the pressure-sensitive adhesive layer comprises at least one hydrophilic monomer, at least one hydrophobic monomer, at least one neutralizing agent and at least one surfactant. Optionally, the acrylic adhesive is treated with a Tg greater than 5°C.

[0028] The hydrophilic acrylic adhesive may be applied to the substrate at a rate of 0.05 gsm to 3.0 gsm. The hydrophilic acrylic adhesive may be applied to the substrate at a rate of 0.05 gsm to 3.0 gsm.

[0029] The PSA adhesive and any attached labels can be removed by peeling off the PSA coated substrate and immersing the sheet in a sodium hydroxide solution having a pH of 12 to 14 and maintained at a temperature below 80°C and continuously stirred. The stirring speed can be at least 100 rpm. After the label is separated from the PET, the floating label portion and the settled PET portion can be separated by filtration.

[0030] Example

[0031] The emulsion mixture was generally prepared by charging 418 g of deionized ("DI") water to a four-liter, five-neck reactor equipped with a condenser, mechanical stirrer, temperature-controlled thermocouple, and initiator and monomer inlets and heating to 90° C. to 92° C. under a gentle nitrogen stream. In a separate container, a monomer emulsion was prepared by mixing 242 g of DI water, 36.63 g of Aerosol A-102, 26.4 g of Siponate DS-4, 3.3 g of sodium hydroxide, and 1,938.14 g of a monomer mixture consisting of 71 wt % 2-ethylhexyl acrylate ("2-EHA"), 26 wt % ethyl acrylate ("EA"), and 3 wt % acrylic acid ("AA"). Next, a solution of a mixture of 1.88 g of sodium carbonate and 10.78 g of sodium persulfate ("NaPS" as an initiator) in 33 g of DI water was added to the reactor, followed by the addition of 15.4 g of a 250 nm sized hydrophobic polymer seed and a 80 nm to 100 nm sized hydrophilic polymer seed and a total of 46.2 g of rinse water. Immediately after the addition of the two polymer seeds, the monomer emulsion was fed into the reactor. The feed was carried out for 150 minutes along with a co-feed solution of 7.92 g of sodium persulfate in 96.8 g of water while maintaining the reaction temperature at 85°C to 87°C. Once 60% of the monomer emulsion was fed into the reactor, 26.84 g of 40 nm to 60 nm hydrophilic seeds were loaded into the reactor followed by a rinse with 11 g of water. After the monomer emulsion addition was complete, the reaction mixture was held for 15 minutes to allow the temperature to drift in the range of 80 to 86 degrees Celsius. After the hold, a solution of 0.019 g FeSO4-7H2O and 0.075 g 42% copper nitrate was added to the reactor as a redox tracking accelerator. Still maintaining the temperature at 80 to 86 degrees Celsius, two tracking solutions were gradually added, one consisting of 7.7 g tert-butyl hydroperoxide (70%) ("t-BHP"), 3.52 g Disponil Fes in 40.37 g DI water, and the other being 2.2 g D(-)-isoascorbic acid (IAA) in 90.2 g DI water, which were fed to the reactor via two separate feeds over a total of 45 minutes. Fifteen minutes into these feeds, a cooling ramp was started to cool the reaction to 55 degrees Celsius over 60 minutes. Fifteen minutes after the end of the tracking feed, a solution of 0.44 g potassium iodate in 12.1 g water was added to the reactor as a biocide stabilizer. Once the reaction temperature reached or was below 55 degrees Celsius, the pH of the reaction was adjusted to 4 to 4.5 by adding 12.32 g of ammonia (28%) neutralizer over 10 minutes.A mixture of 9.9 g Surfynol 440, 41.38 g Disponil Fes-77 and 15.95 g Aerosol OT-75 in 86.46 g water was then added to the batch as a post-addition formulation over 30 minutes. After the reaction was cooled to room temperature, 192.17 g of 10% NaOH solution was added to neutralize the batch to a pH of 7.5 to 8.5 over 30 minutes. At a temperature of <45 degrees Celsius, a biocide package was added. The obtained acrylic dispersion was then filtered through a 100 mesh filter. The obtained acrylic dispersion contained an acrylic polymer consisting of 71 wt % 2-EHA, 26 wt % EA and 3 wt % AA and had a glass transition temperature of -40C with solids between 57% and 59%. The weight percentages are based on the total dry weight of the acrylic polymer.

[0032] Sample conditioning and label lamination

[0033] The prepared, fully formulated wet samples were conditioned for at least 24 hours prior to testing to ensure that no air bubbles were trapped and that the product had time to equilibrate. After 24 hours, the wet adhesive samples were applied to siliconized paper or film by pipette and coated using a knife coating technique at 18 g / m 2 The dry adhesive coating weights were applied as shown in Table 1. The coated adhesive samples were dried in a convection oven at 105°C for two minutes and then conditioned at 50% + / - 5% humidity and 21°C + / - 2°C for approximately four hours. After this conditioning period, the adhesive on the siliconized paper or film was laminated to a (ideally pre-treated) biaxially oriented polypropylene substrate (BOPP) using a hot roll laminator at 40°C and 40atm of pressure. A 12kg weight was then placed on the fully assembled laminate for at least four days. For samples treated with acrylic adhesives with a Tg greater than 5°C, a 2g / m 2 The coating was applied and the BOPP substrate was then dried at 70°C for two minutes.

[0034] PSA Characterization Test Procedure

[0035] The peel adhesion of PSA was determined using the International Federation of Adhesive and Thermocollants Manufacturers and Processors (FINAT) TM”) Test Method Test No. 2. The backing material is removed from a longitudinal strip 25 mm wide and at least 175 mm long, and the adhesive coated facing material is secured to the test panel. The test panel is secured in a horizontal support that is secured to the bottom jaws of the tester. The machine is set to a jaw separation rate of 300 mm per minute, and the machine load averaging function is set to average the data.

[0036] Using FINAT TM Test Method No. 8 Shear resistance testing of standard glass surfaces is performed. A 25 x 25 mm sample strip is attached to a glass plate at a vertical tilt of 2°. The time taken for a 1 kg weight to break the adhesive film inside of the strip is measured.

[0037] Wash-off test procedure

[0038] Using the European PET Bottle Platform (EPBP TM ) Quick Test (QT) 508 procedure tests the washability of the labels. This procedure is a small-scale simulation of the current industrial procedure used by plastic recycling companies. The sample is immersed in a 1% NaOH solution at 80°C or 65°C, stirred at 350 rpm by a magnetic stirrer. The plastic flakes are washed for less than 15 minutes. Optionally, a 0.5% solution of a nonionic surfactant secondary alcohol ethoxylate is added to better disperse the adhesive particles in the liquid and enable better filtration of the plastic flakes.

[0039] All samples of the present invention in Table 1 below contain 0.5% to 2.0% sodium salt of fatty alcohol ether sulfate, >2% acetylenic glycol ethylene oxide / propylene oxide adduct, and >2% sodium dioctyl sulfosuccinate. All samples were neutralized to a latex pH of about 7.6, had about 61.1% solids, a 2@12 grade viscosity of 2420 cP, and a 3@30 grade viscosity of 1764 cP. As shown in the table below.

[0040] Table 1: Composition of Comparative Examples and Inventive Examples

[0041]

[0042]

[0043] Table 2: Characterization of comparative samples and inventive samples

[0044]

Claims

1. A pressure-sensitive adhesive layer comprising at least one hydrophilic monomer, at least one hydrophobic monomer, at least one neutralizing agent and at least one surfactant.

2. The pressure sensitive adhesive of claim 1, wherein the at least one hydrophilic monomer comprises at least 20% of the composition and the at least one hydrophobic monomer comprises at least 50% of the composition.

3. The pressure-sensitive adhesive according to any one of the preceding claims, wherein the at least one hydrophilic monomer is one or more of the group consisting of ethyl (meth)acrylate and (meth)acrylic acid.

4. The pressure-sensitive adhesive according to any one of the preceding claims, wherein the at least one hydrophobic monomer is an alkyl acrylate.

5. The pressure sensitive adhesive according to any one of the preceding claims, wherein the at least one neutralizing agent is NaOH.

6. The pressure-sensitive adhesive according to any one of the preceding claims, wherein the at least one surfactant is a sodium salt of a fatty alcohol ether sulfate.

7. The pressure sensitive adhesive according to any one of the preceding claims, wherein the at least one surfactant comprises at least 0.5% of the composition.

8. The pressure sensitive adhesive according to any one of the preceding claims, further comprising no effective amount of vinyl acetate or a vinyl acetate derivative.

9. The pressure sensitive adhesive of any one of the preceding claims, further comprising an effective amount of a tackifier.

10. A label comprising a substrate and a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive comprises at least one hydrophilic monomer, at least one hydrophobic monomer, at least one neutralizing agent, and at least one surfactant.

11. The label of claim 10 wherein an acrylic adhesive having a Tg greater than 5°C is applied to the substrate.

12. A label according to claim 10 or claim 11, wherein the substrate is one of the group consisting of glass, polyamide, polystyrene, PET, LDPE, LLDPE, PP or HDPEA, and the label washing procedure includes obtaining an article with a label comprising a substrate layer and a pressure-sensitive adhesive layer; the pressure-sensitive adhesive layer comprises at least one hydrophilic monomer, at least one hydrophobic monomer, at least one neutralizing agent and at least one surfactant; optionally, treated with an acrylic adhesive having a Tg greater than 15°C; washing the article under continuous stirring at a temperature below 85°C and a pH between 7 and 14 to remove the label.

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