Pressure sensitive adhesive compositions

Abstract

A pressure sensitive adhesive having improved flame retardancy properties, methods for making same and applications thereof are described. The pressure sensitive adhesive comprises an aqueous based acrylic emulsion and a mixture of halogenated and non-halogenated flame retardants.

Claims

1. A pressure sensitive adhesive composition comprising: (a) 50 wt % to 75 wt % based on the total weight of the composition of an acrylic emulsion; (b) less than 10 wt % based on the total weight of the composition of non-halogenated flame retardants comprising: melamine cyanurate and ammonium polyphosphate; and (c) halogenated flame retardants comprising at least one brominated organic compound; wherein the total amount of melamine cyanurate is from 0.5 wt % to 2.5 wt % based on the total weight of the composition; the total amount of ammonium polyphosphate is from 4 wt % to 9 wt % based on the total weight of the composition; the total amount of brominated organic compound is at least 14.5 wt % based on the total weight of the composition; and the total amount of non-halogenated flame retardants and halogenated flamed retardants is less than 30 wt % based on the total weight of the composition.

2. The pressure sensitive adhesive composition according to claim 1 wherein the total amount of ammonium polyphosphate is from 4 wt % to 6 wt % based on the total weight of the composition.

3. The pressure sensitive adhesive composition according to claim 1 wherein the total amount of non-halogenated flame retardant and halogenated flame retardant is less than 25 wt % based on the total weight of the composition.

4. The pressure sensitive adhesive composition according to claim 1 wherein the acrylic emulsion comprises an acrylic-vinyl acetate co-polymer.

5. The pressure sensitive adhesive composition according to claim 1 wherein the brominated organic compound is selected from the group consisting of: ethylene bis (tetrabromo phthalimide), pentabromo diphenylether, octabromo diphenylether, decabromo diphenylether, tetrabromo bisphenol A, and hexabromo cyclodecane.

6. The pressure sensitive adhesive composition according to claim 1 wherein the melamine cyanurate is present in an amount of 1.4 to 2.5 wt % based on the total weight of the composition.

7. The pressure sensitive adhesive composition according to claim 1 further comprising a tackifier, plasticizer, toughening agent, antioxidant, stabilizer, dye, preservative and/or combinations thereof.

8. An article, comprising a curable film on a release substrate and/or carrier substrate, wherein the curable film comprises the pressure sensitive adhesive composition according to claim 1.

9. A transfer tape comprising a layer of the pressure sensitive adhesive composition according to claim 1 and is attached to a release liner.

10. A pressure-sensitive adhesive tape comprising a backing bearing a layer of pressure sensitive adhesive composition according to claim 1 on at least one side of the backing.

11. The pressure sensitive adhesive composition according to claim 1 wherein the composition is self extinguishing with a burn distance of between about 15 to 25 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings in which:

(2) FIG. 1 shows the FMVSS 302 experimental set up for testing the flame retardancy of prepared sample specimen. The sample specimen comprise two sheets of clear polyethylene terephthalate film between which a test composition is applied.

(3) FIG. 2 shows the burn rate categories for the FMVSS 302 test.

DETAILED DESCRIPTION

(4) As used herein, the term “pressure sensitive adhesive” refers to adhesive compositions which forms a bond when pressure is applied to marry the adhesive with an adherend. No solvent, water, or heat is needed to activate the adhesive. More particularly said term is used for materials or formulations having a glass transition temperature (T.sub.g) of less than 25° C. and a storage modulus G′ of 3.3×10.sup.5 Pa or less at 23° C., wherein the glass transition temperature (T.sub.g) is determined by Differential Scanning calorimetry (DSC) and the storage modulus G′ is determined by Dynamic Mechanical Analysis (DMA) at 1 Hz, and at 23° C.

(5) The acrylic copolymer emulsion can be an acrylate-acrylonitrile dispersion, an ethylene-acrylic acid dispersion, or another acrylate copolymer dispersion.

(6) Monomers for forming the acrylic copolymer emulsion may be represented by the formula:

(7) ##STR00001##
wherein:
R.sup.1 may be selected from hydrogen, halo, or C.sub.1-C.sub.20 aliphatic, which may be substituted or unsubstituted with one or more of halo, amino, hydroxyl, nitrile, C.sub.1-C.sub.5 alkoxy or combinations thereof;
R.sup.2 is nitrile, —O(CO)R.sup.5, —CONHR.sup.5, —SO.sub.2R.sup.5, —CO.sub.2R.sup.5, —(CO)—R.sup.5 where R.sup.5 is hydrogen or C.sub.1-C.sub.20 aliphatic, which may be substituted or unsubstituted with one or more of halo, amino, hydroxyl, nitrile, C.sub.1-C.sub.5 alkoxy or combinations thereof;
R.sup.3 is H or C.sub.1-C.sub.8 alkyl; and
R.sup.4 is H or C.sub.1-C.sub.8 alkyl.

(8) R.sup.1 may be hydrogen, or C.sub.1-C.sub.10 alkyl, for example, methyl, ethyl, propyl or butyl.

(9) R.sup.2 may be an ester such as —CO.sub.2R.sup.5 or —O(CO)R.sup.5.

(10) R.sup.3 may be hydrogen, or C.sub.1-C.sub.10 alkyl, for example, methyl, ethyl, propyl or butyl.

(11) R.sup.4 may be hydrogen, or C.sub.1-C.sub.10 alkyl, for example, methyl, ethyl, propyl or butyl.

(12) R.sup.5 may be hydrogen, or C.sub.1-C.sub.10 alkyl, for example, methyl, ethyl, propyl or butyl.

(13) Suitably, the monomeric acrylic component of the acrylic copolymer emulsion may be (meth)acrylic acid, C.sub.1-C.sub.8 alkyl (meth)acrylate, or C.sub.1-C.sub.13 hydroxyalkyl (meth)acrylate. Suitably, the acrylic component may be acrylic acid or methacrylic acid.

(14) The monomeric non-acrylic component of the acrylic copolymer emulsion may for example be at least one of a vinyl ester, such as vinyl acetate, methyl vinyl acetate, ethyl vinyl acetate.

(15) The acrylic emulsion is suitably, an aqueous emulsion.

(16) The viscosity of the emulsion is suitably less than 2000 mPa.Math.s when measured at 23° using a Brookfield Viscometer and RV-2 Spindle at 50 rpm. This facilitates application of the emulsion to a substrate.

(17) The glass transition temperature (Tg) of the acrylic copolymer as determined using differential scanning calorimetry is less than 0° C., suitably from −20 to −60° C. For example, the Tg may be approximately −30° C., or −40° C., or −50° C. If the Tg is greater than 0° C., the acrylic copolymer will no longer be tacky at room temperature.

(18) Acrylate-acrylonitrile dispersions are available under the trade names Saitek® 400, manufactured by Saiden Technologies; or Acronal® 35D, Acronal® 81D, Acronal® A200, Acronal® A220, Acronal® A280, Acronal® A323, Acronal® A378, Acronal® A380, Acronal® B37D, or Acronal® DS3390, all manufactured by the BASF Corporation. Ethylene-acrylic acid dispersion products are available under the trade names Adcote® 50T4983 or Adcote® 50T4990, both manufactured by Morton International. Suitably acrylate copolymer emulsions are sold under the trade names Acronal® 210 or Acronal® V275, both manufactured by the BASF Corporation. Two alternative commercially available acrylic emulsions are provided by Momentive, namely those provided under the trade name Synthebond® E-2050 and Synthebond®-7701.

(19) The compositions of the invention may further comprise tackifiers, thickeners, defoaming agents, dispersing agents, toughening agents, antioxidants, stabilizers, dyes, preservatives and/or combinations thereof.

(20) Suitable tackifiers are known to persons skilled in the art. Sources of tackifiers can be found in standard publications on pressure sensitive adhesives, for example, the “Handbook of Pressure Sensitive Adhesive Technology” from Donata Satas (van Notstrand, New York, 1989).

(21) Examples of filler components include but are not limited to, for example, silicas, quartz, alumina, calcium magnesium carbonate, calcium silicate hydrate, calcium carbonate, clays, talcs and other inorganic filler materials such as polycarbonates and other polymer powders, along with certain acrylate components.

(22) Examples of stabiliser components which may be suitably used in the adhesive film of the present invention include hydroquinone, pyrocatechol, resorcinol or derivatives thereof, phenols, sulfur dioxide, sulfuric acid, alkyl sulfonic acids, aromatic sulfonic acids, boranes and combinations thereof. For example, the stabiliser may be selected from methanesulfonic acid (MSA), BF.sub.3, SO.sub.2 and combinations thereof. Suitably, the stabiliser may be selected from camphor sulfonic acid (CSA) or hydroquinone and combinations thereof.

(23) Useful thickeners include oliginates, bentonite, casein, fumed silica, guar gum, gum tragacanth, hydroxyethyl cellulose, locust bean gum, methylcellulose, polyacrylic acid salts (e.g., ammonium, potassium, sodium salts), polyvinyl alcohol, sodium carboxymethyl cellulose, and starches.

(24) Defoamers, defoaming agents or foam inhibitors in the context of the invention are substances which are added to foaming liquids to reduce their foaming or to prevent them from foaming. They are either interfacially active substances which displace the foam generators from the interface without themselves producing any foam or products which increase the surface tension of water, for example natural fats and oils or fatty alcohols. The use of the defoamers is not absolutely essential, but is nevertheless helpful. For example, long-chain soaps, such as sodium behenate, may be used as the defoamer. Other suitable defoamers include mineral oils, and compounds based on silicone, such as silicone oils. Suitably, defoamer includes polyethylene/propylene glycol ethers which are known commercially as Pluronics®, and the corresponding mixed ethers of these compounds. If present the defoamer is employed in typically 1 wt % or less based on the total weight of the composition.

(25) The present invention also provides for articles comprising the pressure sensitive adhesive composition of the invention. For example, the present invention provides for articles comprising a curable film on a release substrate and/or carrier substrate, wherein the curable film comprises the pressure sensitive adhesive composition according to the invention.

(26) The article may be an adhesive tape, a transfer tape, a label or laminate comprising the pressure sensitive adhesive composition according to the invention.

(27) In one embodiment, the transfer tape may comprise a layer of the pressure sensitive adhesive composition according to the invention, which is attached to a release substrate (or release liner).

(28) In a further embodiment, the pressure-sensitive adhesive tape comprising a backing bearing a layer of pressure sensitive adhesive composition according to the invention is provided, wherein said composition is provided on at least one side of the backing.

(29) The release substrate may be paper, or plastic based (e.g. PET, PE, HDPE, and PP) materials, which are optionally coated with a release agent.

(30) Release agents allow the adhesive films of the article of the present invention to be easily transferred from the release substrate to the article of interest. The release agent may be selected from the group consisting of polyvinyl alcohol, clays, siloxanes, and combinations thereof. Suitable release agents, in particular siloxane-based release agents, are available under the trade name SILCOLEASE®.

(31) As used herein, the term carrier substrate refers to a material onto which a curable film of the pressure sensitive adhesive of the invention can be coated so as to allow for handling of the adhesive. The carrier substrate can add mechanical strength to the article so as to improve handling.

(32) The carrier substrate may be flexible, for example a flexible sheet. The carrier substrate may be selected from polymeric films, metal foils, foams, cloths, and combinations thereof. For example, the carrier substrate may be selected from the group consisting of polyester, polypropylene, polyethylene, foam and paper.

Examples

(33) As used above and below, the term flame-retardant pressure sensitive adhesive refers to pressure-sensitive adhesive compositions in which basic flammability has been reduced by adding a flame-retardant system and is measured according to Federal Motor Vehicle Safety Standard FMVSS 302. ISO 3795 is a technically equivalent standard used in Europe, Canada, and Japan; while ASTM D5132-04 is used in the US. The FMVSS 302 specifies the burn resistance requirements for materials used in the occupant compartments of motor vehicles (La, passenger cars, multipurpose passenger vehicles, trucks and buses).

(34) Compositions were prepared and subsequently tested in accordance with FMCSS 302. The compositions were prepared as outlined below:

(35) Water and optional additives such as a defoamer and dispersing agents were mixed at high speed with a laboratory mixer and then the non-halogenated flame retardants (i.e. melamine cyanurate and ammonium polyphosphate) and the halogenated flame retardants (i.e. at least one brominated organic compound) were added at lower speed to avoid foaming. Mixing was continued until homogeneous. In the next step, the acrylate emulsion(s) was/were added and the resulting mixture was stirred at lower speed until a homogeneous product was formed.

(36) The acrylic emulsions may be any of those described herein, though in the below examples, those provided under the trade names Synthebond™ E 2050 and Acronal™ V 275 were employed. A suitable source of melamine cyanurate is that provided under the trade name Budit™ 315. A suitable source of ammonium polyphosphate is FR Cros S10™. The brominated organic compound may be any of those described herein, though in the below examples, that provided under the trade name Saytex® BT 93 W was employed. As outlined above, any suitable defoaming agent may be used in the compositions of the invention, though in the below examples, that provided under the trade name Byk®-1640 was used. Similarly, any suitably dispersing agent may be used in the compositions of the invention, though in the below examples, that provided under the trade name Disperbyk®-2010 was employed.

(37) Test Procedure

(38) Sample specimens were prepared as follows:

(39) A test composition is applied to a clear polyethylene terephthalate (PET) film (thickness of ˜0.0564 mm, width ˜15.2 cm) using a 5 mL pipette. The composition is spread evenly with an applicator rod (wire wound wet film applicator rod 20″ (51.3 microns wet film thickness) over the film. The PET film with the sample evenly spread thereon, is then dried in an oven at 80° C. for approximately 5 minutes. Once removed from the oven, the specimen is allowed to cool to room temperature and a second sheet of clear PET film is applied to the composition on the first sheet of PET film, thereby forming a sandwich structure of two PET films with the adhesive composition therebetween. The two films were then bonded together by applying pressure to the sandwich using a roller.

(40) Each specimen is then tested according to FMVSS 302. Each specimen is placed in a U-shaped holder and fixed with clamps. The specimen is burned with a butane gas burner whose flame has been adjusted to a 3-5 cm long blue area. Each specimen is burned for 15 seconds. The space between burner and foil ˜38 mm. Each specimen is assessed according FMVSS 302.

(41) The test is conducted inside a test chamber where the test specimen is mounted horizontally. The exposed side of the test specimen is subjected to a gas flame from underneath. As shown in FIG. 2, the burn distance and the time taken to burn this distance is measured during the test. The result, the burning rate, is expressed in mm/min. Categories of burning are expressed as follows: DNI=does not ignite; SE=self-extinguishing; SE/NBR=self-extinguishing/no burn rate; SE/BR=self-extinguishing with burn rate; BR=burn rate. For the compositions of the invention, an acceptable burn rating is SE, with the best burn distance being around 15-25 mm.

(42) Lap Shear Strength

(43) Lap shear strengths were determined in accordance with ASTM D1002-05 or ASTM D3163.

(44) PET film was coated with a sample adhesive composition to create a 0.001″ (0.025 mm) wet film thickness. The composition was dried for 5 minutes at 85° C. After cooling, the film with the composition thereon was cut into 1″ (25.4 mm) wide strips. Two strips were adhesively mated to create a 0.5″ (12.7 mm) overlap. The mated area was pressed using a weighted roller, rolling one time parallel to the overlapping area and one time perpendicular to the overlapping area. After curing for one day at room temperature under standard conditions, specimens were placed in the grips of a universal testing machine and pulled at 2.36″ (60 mm) per minute cross head speed.

(45) TABLE-US-00001 TABLE 1 Composition No./Amt (wt %) Raw materials 1 2 3 4 5 6 7 Acronal ™ V 275 25.45 25.45 25.41 25.25 25.25 25.25 31.90 Synthebond ™ E 2050 25.45 25.45 25.41 25.25 25.25 25.25 31.90 Ammonium hydroxide 27% 0.40 0.40 0.40 0.42 0.42 0.42 0.31 Disperbyk ™ 2010 0.20 0.20 2.19 0.72 0.50 0.50 1.23 Byk ™ 1640 0.10 0.10 0.25 0.10 0.22 0.22 0.31 Saytex ™ BT 93 W 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Budit ™ 315 0.00 0.00 2.50 1.50 9.00 13.40 1.84 FR Cros S-10 ™ 19.46 22.45 22.42 25.30 17.80 13.40 6.13 Water 28.94 25.95 21.42 21.46 21.56 21.56 26.38 Burn Distance [mm] 280 75 30 30 70 280 280 Burn Rate BR SE/NBR SE SE SE/NBR BR BR

(46) Compositions 1 and 2 do not comprise either melamine cyanurate or a brominated organic compound as flame retardant. Said compositions did not pass the FMVSS 320 test i.e. said compositions were not self-extinguishing under the test conditions.

(47) Compositions 3 to 7 comprise varying amounts of melamine cyanurate and ammonium polyphosphate but do not comprise a brominated organic compound as flame retardant. While compositions 3 and 4 passed the FMVSS 320 test i.e. said compositions were self-extinguishing under the test conditions, the adhesive performance of said compositions was sub-optimal, with tackiness being adversely affected.

(48) Furthermore, compositions comprising only melamine cyanurate and ammonium polyphosphate (i.e., compositions 3 to 7) demonstrated reduced tackiness. The viscosity of said compositions was also too high for the desired applications.

(49) TABLE-US-00002 TABLE 2 Composition No./Amt (wt %) Raw materials 8 9 10 11 12 13 14 15 16 Acronal ™V 275 28.42 28.42 28.42 28.42 28.42 28.42 28.42 28.42 28.42 Synthebond ™ E 2050 28.42 28.42 28.42 28.42 28.42 28.42 28.42 28.42 28.42 NH4 + OH— 27% 0.27 0.27 0.27 0.27 0.27 0.27 0.27 0.27 0.27 Disperbyk ™2010 1.09 1.09 1.09 1.09 1.09 1.09 1.09 1.09 1.09 Byk ™ 1640 0.28 0.28 0.28 0.28 0.28 0.28 0.28 0.28 0.28 Saytex B ™T 93 W 8.36 9.95 10.52 10.89 11.22 12.62 13.12 13.61 14.28 Budit ™315 1.31 0.62 1.50 1.70 0.40 1.80 1.17 0.34 0.89 FR Cros S-10 ™ 8.36 7.46 6.01 5.44 6.41 3.61 3.74 4.08 2.86 Water 23.49 23.49 23.49 23.49 23.49 23.49 23.49 23.49 23.49 Burn Distance [mm] 170 280 280 270 270 280 280 280 280 Burn Rate BR BR BR BR BR BR BR BR BR

(50) TABLE-US-00003 TABLE 3 Composition No./Amt (wt %) Raw materials 17 18 19 20 21 22 23 24 Acronal ™ V 275 26.06 25.72 26.10 25.39 25.86 25.00 25.25 25.29 Synthebond ™ E 2050 26.06 25.72 31.30 25.39 25.86 25.00 25.25 25.29 NH.sub.4OH 27% 0.24 0.24 0.39 Disperbyk ™2010 2.25 2.22 1.15 2.19 2.12 0.96 0.97 2.09 Byk ™ 1640 0.22 0.22 0.21 0.21 0.20 0.24 0.24 0.24 Saytex BT 93 W 14.80 15.42 15.66 16.02 18.18 19.23 19.42 19.46 Budit ™ 315 1.94 2.02 2.09 2.10 1.52 1.44 2.91 1.46 FR Cros S-10 ™ 7.15 7.45 5.74 7.74 5.05 7.21 4.85 4.86 Water 21.52 21.23 17.75 20.96 21.21 20.68 20.87 20.92 Burn Distance [mm] 26 17 19 13 30 24 45 16 Burn Rate SE SE SE SE SE SE SE/NBR SE Lap shear [psi] — — 53.6 ± 5.1 57.3 ± 3.7 — — — — Composition No./Amt (wt %) Raw materials 25 26 27 28 29 30 31 Acronal ™ V 275 25.43 25.81 26.26 26.94 23.32 21.40 25.83 Synthebond ™ E 2050 25.43 25.81 26.26 26.94 23.32 21.40 28.93 NH.sub.4OH 27% 0.24 0.25 0.25 0.26 0.22 0.21 — Disperbyk ™2010 0.98 0.99 1.01 1.04 0.90 0.82 1.14 Byk ™ 1640 0.24 0.25 0.25 0.26 0.22 0.21 0.21 Saytex BT 93 W 19.56 19.85 20.20 20.73 26.91 32.92 15.50 Budit ™ 315 2.20 0.74 1.52 1.55 1.35 1.23 2.07 FR Cros S-10 ™ 4.89 4.96 2.53 0.00 4.48 4.12 6.71 Water 21.03 21.34 21.72 22.28 19.28 17.69 19.63 Burn Distance [mm] 35 20 108 280 18 15 18 Burn Rate SE SE SE/NBR BR SE SE SE Lap shear [psi] — — — — — — 53.6 ± 2.6

(51) As is evident from Table 2, when the brominated organic compound is present in less than 14.5 wt % the compositions performed poorly. Table 3, when the brominated organic compound was added at levels of over 14.5 wt % based on the total weight of the composition, the fire retardancy of said compositions generally improved. However, as is clear from compositions 26, 27 and 28, insufficient or the absence of ammonium polyphosphate results in inferior compositions from a flame retardancy standpoint. The test results for composition 23 demonstrate that when greater than 2.5 wt % melamine cyanurate was present the fire burn rate was also increased. Optimal results were achieved when ammonium polyphosphate was present in an amount of from 4 wt % to 9 wt % and when melamine cyanurate was present in an amount of from 0.5 wt % to 2.5 wt %, each based on the total weight of the composition.

(52) Interestingly, when the amount of melamine cyanurate was increased above 2.5 wt % based on the total weight of composition, longer burn distances were observed. In addition, when the amount of ammonium polyphosphate is from 4 wt % to 6 wt % based on the total weight of composition, enhanced adhesive performance was observed.

(53) Desirably, when the lap shear strength of compositions of the invention was assessed, said compositions had lap shear strengths in excess of 50 psi (0.345 MPa) or greater as determined in accordance with ASTM D1002-05 or ASTM D3163.

(54) The words “comprises/comprising” and the words “having/including” when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

(55) It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.