Flame retardant adhesives for films

Abstract

A film includes an adhesive layer having an adhesive polymer, a polyphosphonate, and an organophosphate on a substrate layer, where the adhesive layer is optically clear and has low flammability.

Description

[0001] The present disclosure relates to adhesives for films, and in particular to flame retardant adhesives for films.

[0002] Adhesives have been used for a variety of marking, securing, protecting, sealing, and masking purposes. Adhesive tapes generally include a backing or substrate and an adhesive. One class of adhesives, pressure-sensitive adhesives, is particularly useful for many applications.

[0003] Pressure sensitive adhesive is well known to those of ordinary skill in the art, and it has some comprising the following characteristics at room temperature: (1) powerful and lasting tack, (2) just can adhere with finger pressing, (3) enough ability to remain on adherend, and (4) enough cohesive strength to remove cleanly from adherend.It has been found that the material used as pressure sensitive adhesive well is to show required viscoelastic property through design and preparation, thereby makes viscosity, peel adhesion and shear strength reach the polymer of expectation balance.The most commonly used polymer for preparing pressure sensitive adhesive is natural rubber, synthetic rubber (for example, styrene / butadiene copolymer (SBR) and styrene / isoprene / styrene (SIS) block copolymer), various (methyl) acrylate (for example, acrylate and methacrylate) copolymer and organosilicon.These types of materials each have advantages and disadvantages. Summary of the Invention

[0004] The present disclosure provides a film that can be optically clear and have low flammability.

[0005] In one aspect, the film includes a substrate layer and an adhesive layer on the substrate layer. The adhesive layer comprises an adhesive polymer, a polyphosphonate, and an organic phosphate. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] To easily identify the discussion of any particular element or act, the most significant digit(s) in a reference number refers to the figure numeral that first introduces that element.

[0007] Figure 1 Aspects of the subject matter according to one embodiment are illustrated. DETAILED DESCRIPTION

[0008] The use of adhesives, especially pressure-sensitive adhesives, is becoming increasingly widespread. Areas where adhesive use is increasing include the medical, electronics, and optical industries, as well as consumer products and public transportation. These industries require adhesives to have specialized properties. For example, adhesives (such as pressure-sensitive adhesives) are required to have specialized properties that surpass conventional tack, peel adhesion, and shear strength. To meet the increasingly stringent performance requirements placed on adhesives, a variety of new materials are needed. Among these performance requirements are optical clarity and flame retardancy. Adhesives are often required to have optical clarity because the adhesive layer is often a component of an optical article or device; and adhesives are also required to have flame retardancy to inhibit or slow the spread of fire and thereby protect people and property. In various applications, such as for graphic films or outer laminates, some adhesives, such as acrylic adhesives, can have a significant impact on overall flammability, especially when the mass of the adhesive constitutes a relatively significant percentage of the construction. Reducing the flammability of the adhesive can significantly reduce the flammability of the entire construction, particularly with respect to combustion calorimetry.

[0009] Adhesives of the present disclosure can be used in films to provide flame retardancy, optical clarity, and adhesive properties in various applications. Applications can include applying a transparent adhesive layer to a base layer, and applying the structure to a substrate. Non-limiting examples of applications include being used for outer lamination films, surface protection films, window films, or other glass surface films. In some embodiments, the adhesive can be used to form an adhesive layer comprising an adhesive polymer, a polyphosphonate, and an organic phosphate.

[0010] Figure 1 An example of a film 102 according to the present disclosure applied to a substrate 108 is shown. Film 102 includes a base layer 104 and an adhesive layer 106. Adhesive layer 106 can provide suitable adhesion properties between base layer 104 and substrate 108 for a particular application. Base layer 104 can be a polymer film. Non-limiting examples of polymer films include polyester, vinyl, polyolefin, polyurethane, acrylic, polylactic acid, or combinations thereof, or multilayer films.

[0011] The various layers of the film 102 can be selected based on the application and the type of substrate 108. The film 102 can be applied to various types of substrates 108. In some embodiments, the substrate 108 is a polymer or metal substrate. Non-limiting examples of polymeric substrates include various types of layered materials such as polyester, vinyl, polyolefin, polyurethane, acrylic, polylactic acid, or combinations thereof. Non-limiting examples of metal substrates include aluminum.

[0012] Various forms of the film 102 include tapes, multilayer films with additional layers (such as low adhesion coatings), etc. Such applications may provide the film 102 in the form of a sheet or a roll.

[0013] In some embodiments, to provide suitable adhesive properties, the adhesive layer 106 can have a peel adhesion (force / length) greater than or equal to 350 N / m, 525 N / m, 700 N / m, 875 N / m, 1050 N / m, 1225 N / m, 1400 N / m, 1575 N / m, or even 1750 N / m, particularly when laminated to a polymer metal substrate. In some embodiments, the peel adhesion is less than or equal to 1925 N / m, 1750 N / m, 1575 N / m, 1400 N / m, 1225 N / m, 1050 N / m, 875 N / m, 700 N / m, or even 525 N / m. Peel Adhesion is defined using measurements from the Peel Adhesion Test Method and is applicable over a variety of timeframes and conditions, including 24 hours at ambient temperature and humidity (23° C. and 50% relative humidity), 7 days at ambient temperature and humidity, or 7 days at 65° C. In many applications, a peel adhesion of greater than or equal to 350 or 525 at 24 hours at ambient temperature and humidity may be particularly desirable.

[0014] In some embodiments, when tested on a metal substrate (e.g., aluminum), the peel adhesion is at least 1050 N / m at ambient temperature and humidity for 24 hours and at least 700 N / m at 65° C. for 7 days. In one or more embodiments, when tested on a metal substrate (e.g., aluminum), the peel adhesion is at least 1400 N / m at ambient temperature and humidity for 24 hours and at least 700 N / m at 65° C. for 7 days.

[0015] In some embodiments, when tested on a polymeric substrate (e.g., vinyl), the peel adhesion is at least 700 N / m after 24 hours at ambient temperature and humidity, and at least 700 N / m after 7 days at 65° C. In one or more embodiments, when tested on a metal substrate (e.g., aluminum), the peel adhesion is at least 700 N / m after 24 hours at ambient temperature and humidity, and at least 1050 N / m after 7 days at 65° C.

[0016] Generally speaking, when laminated to a polymeric or metallic substrate, the peel adhesion of the adhesive layer 106 of the film 102 is greater than the peel adhesion of the adhesive layer 106 that is free of the polyphosphonate and the organophosphate.

[0017] The substrate 104, the adhesive layer 106 or both may be optically clear. As used herein, the term "optically clear" refers to high light transmittance over at least a portion of the visible light spectrum (about 400 nm to about 700 nm) and exhibits low haze. Typically, optically clear articles have a visible light transmittance of at least 90%, 91%, 92%, 93%, 94% or even 95%, and a haze of less than or equal to 5%, 3%, 2% or even 1.5%. Haze is defined using measurements from a haze test method. In some embodiments, the adhesive layer 106 has a transmittance of at least 92% and a haze of less than or equal to 3%.

[0018] The thickness of the adhesive layer 106 can be selected based on the desired haze %. Appropriate thickness and haze % can be selected based on the application by one of ordinary skill in the art having the benefit of this disclosure.

[0019] Base layer 104, adhesive layer 106 or both can be optically transparent. As used herein, the term "optically transparent" refers to a high light transmittance on at least a portion of the visible light spectrum (about 400nm to about 700nm). Typically, optically transparent products have a visible light transmittance of at least 80%. The term "transparent film" refers to a film with a certain thickness, and when the film is arranged on a substrate, an image (arranged on or adjacent to a substrate) is visible through the thickness of the transparent film. In many embodiments, a transparent film allows the image to be seen through the thickness of the film without significantly losing image clarity. In some embodiments, the film has a matte surface or a glossy surface. When film 102 is transparent, base layer 104 and adhesive layer 106 are both transparent. In other embodiments, base layer 104 can be opaque or have a light transmittance lower than 80%.

[0020] The substrate layer 104, the adhesive layer 106, or both can be colorless. As used herein, the term "colorless" refers to a color difference (ΔE or ΔE*) of less than 1 according to a color test method. In some embodiments, the substrate layer 104, the adhesive layer 106, or both have a ΔE* of less than or equal to 2, 1.5, 1, 0.75, or even 0.7. In some embodiments, the adhesive layer 106 has a ΔE* of less than or equal to 0.7. In other embodiments, the substrate layer 104 or the adhesive layer 106 may have a color or be described as colored (e.g., a ΔE* greater than 2).

[0021] Adhesive layer 106 includes at least an adhesive polymer, a polyphosphonate as a first flame retardant additive, and an organic phosphate as a second flame retardant additive. The adhesive polymer can be selected to be suitable for use in pressure-sensitive adhesives or hot melt adhesives. In some embodiments, the adhesive polymer includes one or more acrylic acids for pressure-sensitive adhesives, such as 2-ethylhexyl acrylate (2-EHA). In particular, the adhesive polymer can include a polymer chain formed by reacting one or more acrylates and acrylic acid (AA). In one example, the adhesive polymer includes 90% 2-ethylhexyl acrylate (2-EHA) and 10% AA, based on the weight of the adhesive polymer (the total weight of the monomers in the adhesive polymer does not include any solvent).

[0022] The halogen-free polyphosphonate can be included in the adhesive layer in various suitable amounts. In some embodiments, the polyphosphonate is greater than or equal to 5%, 10%, 15%, or even 20% by weight of the adhesive layer (the total weight of the adhesive layer after drying or curing, where the total weight of the adhesive layer is the sum of the weights of the adhesive polymer, the polyphosphonate, and the organophosphate). The polyphosphonate can be less than or equal to 30%, 25%, 20%, 15%, or even 10% by weight of the adhesive layer.

[0023] The polyphosphonate may include oligomers having a molecular weight (MW) greater than 7500, 8000, or even 8500. The MW may be less than or equal to 10000, 9500, or even 9000. The polydispersity index (PI) of the polyphosphonate may be less than 4, 3.5, 3, or even 2.75. The PI may be greater than or equal to 1.5, 2, or even 2.5. In some embodiments, the polyphosphonate is a non-cyclic polymer. In some embodiments, the polyphosphonate does not contain alcohol functional groups. Non-limiting examples of suitable polyphosphonates include Nofia HM5000 flame retardant additives available from FRX Polymers, Inc., Chelmsford, MA.

[0024] The halogen-free organophosphate can be included in the adhesive layer in various suitable amounts. In some embodiments, the organophosphate comprises greater than or equal to 5%, 10%, 15%, or even 20% by weight of the adhesive layer (the total weight of the adhesive layer after drying or curing, where the total weight of the adhesive layer is the sum of the weights of the adhesive polymer, polyphosphonate, and organophosphate). The organophosphate can comprise less than or equal to 30%, 25%, 20%, 15%, or even 10% by weight of the adhesive layer.

[0025] The organophosphate can be any suitable organophosphate that reduces the stiffness of the adhesive layer. An example of an organophosphate is a phosphate ester, such as tetraphenylresorcinol bis(diphenyl phosphate). Non-limiting examples of suitable organophosphates include TEXFRON 5001 flame retardant additive available from ICL Industrial Products America Inc., St. Louis, MO.

[0026] In general, the adhesive polymer and the flame retardant additive are selected to be compatible to provide an optically clear adhesive layer 106 with low flammability, particularly in terms of combustion calorimetry as measured by the Micro Combustion Calorimetry test method. In general, to provide sufficient flame retardancy, the adhesive layer 106 has a sufficient amount of the flame retardant additive selected by one of ordinary skill in the art having the benefit of this disclosure.

[0027] Compatibility can be indicated by the lack of a melting endotherm, particularly as measured by the differential scanning calorimetry test method. In some embodiments, the adhesive layer 106 does not have a melting endotherm, particularly at temperatures above 373K, or at temperatures between 100°C and 150°C. Generally speaking, the lack of a melting endotherm can be correlated with a low haze %. In some embodiments, the optically clear adhesive layer 106 can have polymer chains formed by reacting 2-EHA and 10% AA by weight of the adhesive polymer with a total of about 20% polyphosphonate and organophosphate as additives (e.g., 10% polyphosphonate and 10% organophosphate) by weight of the adhesive layer.

[0028] Film 102 can be made in any suitable manner. Generally, the components of the adhesive polymer can react to form a solution comprising the adhesive polymer. Flame retardant additives including polyphosphonates and organophosphates can be added to the solution. The solution can then be applied to substrate 104, dried, and cured to form adhesive layer 106 on substrate 104. Film 102 can then be used in various applications.

[0029] Example

[0030] Flame retardant pressure-sensitive adhesive compositions and films coated with the adhesive were prepared and their material properties were characterized. These examples are for illustrative purposes only and are not intended to limit the scope of the appended claims. Unless otherwise indicated, all parts, percentages, ratios, etc. in the examples and the remainder of the specification are by weight. Unless otherwise indicated, the solvents and other reagents used were obtained from Sigma-Aldrich Chemical Company, St. Louis, Missouri. The following abbreviations are used herein: ° C = degrees Celsius; h = hours; min = minutes; kPa = kilopascals; N / m = Newton / meter; ΔE* = color difference; K / sec = degrees Kelvin / second; J / gK = Joule / gram Kelvin; K = degrees Kelvin; K = degrees Kelvin; kJ / g = kilojoule / gram; mJ / cm 2 = millijoules / square centimeter.

[0031] Materials List

[0032]

[0033] Haze test method

[0034] Haze, clarity, and transmittance were measured according to ASTM D 1003-13 using a BYK Haze-Gard Plus Model AT-4725 (available from BYK-Gardner, Columbia, Md.) The adhesive was coated directly onto polyester film and measured.

[0035] Color test methods

[0036] The color difference of the adhesive was measured using an X-RITE spectrophotometer model Ci62 (available from X-Rite, Grand Rapids, MI) at D65 / 100 illuminant / observer according to ASTM D2244-16. The color shift (DE*) of a film-backed adhesive sample laminated to a white vinyl film (available as a 3M CONTROLTAC IJ180MC-10 from 3M, St. Paul, MN) was calculated from the measured CIELAB color space values using the neat adhesive as a reference according to the following equation:

[0037]

[0038] Peel Adhesion Test Method

[0039] Peel adhesion was measured according to ASTM D330-04 using an INSTRON Model 5965 (available from Instron, Norwood, MA). Film-backed adhesive samples were cut into 25.4 mm wide strips and applied manually with a doctor blade to either a Q-Panel aluminum panel (available from Q-Lab, Westlake, OH as 6061T6 SP-104177) or a vinyl-covered aluminum panel (available from 3M, St. Paul, MN as 3M CONTROLTAC IJ180MC-10). The samples were conditioned for the specified dwell time in an oven set to constant temperature and humidity (23°C and 50% relative humidity) or at 65°C. After the specified conditioning, peel adhesion was measured by peeling the sample from the substrate at a 180-degree angle at a removal rate of 30.5 cm / min. Peel adhesion is measured in pounds-force per inch (lbf / in) and converted to Newtons per meter (N / m).

[0040] Micro Combustion Calorimetry (MCC) Test Method

[0041] The flammability of the adhesive was measured using a Microscale Combustion Calorimeter Model MCC-2 (available from Govmark, Farmingdale, NY) according to ASTM D7309-13, Method A. A 2-3 mg sample of the cured adhesive was heated at a rate of 1 K / s in a nitrogen atmosphere. The decomposition products were completely oxidized in a combustion chamber maintained at 900°C in an atmosphere of 20% oxygen and 80% nitrogen. The heat release of the decomposition gases was determined by the mass of oxygen used to completely combust the sample. The following parameters were calculated from the data:

[0042] Heat release capacity ηc (J / gK), which is the maximum specific heat release rate divided by the heating rate.

[0043] Specific heat release hc (kJ / g), which is the net heat release over the entire temperature range.

[0044] Pyrolysis residue Yp (%), which is the mass fraction of the sample remaining after the test.

[0045] Differential Scanning Calorimetry (DSC) Test Method

[0046] The thermal properties of the adhesives were measured using a Differential Scanning Calorimeter DSC2500 Discovery Series from TA Instruments (New Castle, DE).

[0047] 3 to 5 mg of the cured adhesive sample was removed from the release liner and placed directly into a cup and then into the autosampler. The sample was subjected to a heating profile from 193 K to 423 K at a linear heating rate of 3 K / min or 20 K / min in a nitrogen atmosphere.

[0048] The resulting DSC graph is analyzed for the presence of a melting endotherm, typically above 393 K, as an indication of the compatibility between the flame retardant additive and the polymer.

[0049] Example Preparation

[0050] Example E1

[0051] A flame retardant adhesive solution was prepared by mixing 2-EHA and AA with AEBP (0.35 phr, 1.05 g, a 50% solution in ethyl acetate), Vazo 67 initiator (0.15 phr, or 0.225 g), and Irganox 1010 (0.15 phr, 0.23 g) by weight in a 1-liter amber bottle according to the ratios in Table 1. Isopropyl alcohol and ethyl acetate were added to target a total monomer concentration of 50% by mass (total monomer + solvent solution = approximately 300 g). The amber bottle was capped with a PTFE-lined cap, and the contents of the amber bottle were thoroughly mixed, the cap removed, and the solution degassed by bubbling a constant stream of nitrogen (approximately 1 L / min) through the solution for two minutes. The amber bottle was again sealed with a PTFE-lined cap and placed in a Launder-Ometer available from Atlas Electric Devices Co., Chicago, IL, containing a 60°C water bath. TM (Model M228AA) for 20 to 24 hours. FR additives FRA1 and FRA2 were then added by weight percentage, with the solution diluted to 47.6% ± 0.5% solids with ethyl acetate. The solution was coated onto LI using a knife coater with a gap of 203 microns and dried in an oven set at 65°C for 10 minutes. The dried coating was then passed through a Honle JetCURE UV curing unit (available from Honle UV America, Inc., Marlboro, MA) under a stream of nitrogen to receive a dose of 60 mJ / cm2 of UVC light. The cured adhesive-coated release liner was laminated to the film substrate using a laminator at a nip pressure of 276 kPa at a speed of 0.9 to 1.5 meters per minute.

[0052] Table 1. Examples of polyphosphonate flame retardant adhesives

[0053] Example No. 2-EHA BA MA AA FRA1 FRA2 base E1 90 0 0 10 10％ 10％ F1

[0054] Comparative Examples C0-C2

[0055] A comparative adhesive solution was prepared by mixing 2-EHA and AA with AEBP (0.35 phr, 1.05 g, a 50% solution in ethyl acetate), Vazo 67 initiator (0.15 phr, or 0.225 g), and Irganox 1010 (0.15 phr, 0.23 g) by weight in a 1-liter amber bottle according to the ratios in Table 2. Isopropyl alcohol and ethyl acetate were added to target a total monomer concentration of 50% by mass (total monomer + solvent solution = approximately 300 g). The amber bottle was capped with a PTFE-lined cap, and the contents of the amber bottle were thoroughly mixed, the cap removed, and the solution degassed by bubbling a constant stream of nitrogen (approximately 1 L / min) through the solution for two minutes. The amber bottle was again sealed with a PTFE-lined cap and placed in a Launder-Ometer available from Atlas Electric Devices Co., Chicago, IL, containing a 60°C water bath. TM (Model M228AA) for 20 to 24 hours. The FR additive was then added as per weight percentage for C2. The solution was diluted to 47.6 ± 0.5% solids with ethyl acetate. Comparative Example C0 was a 3 mil PET film without an adhesive coating. The solution was similarly coated and laminated onto a film substrate as described in Example E1.

[0056] Table 2. Comparative Examples of Adhesives

[0057] Example No. 2-EHA BA MA AA FRA1 FRA2 base C0 0 0 0 0 0％ 0％ F2 C1 90 0 0 10 0％ 0％ F1 C2 90 0 0 10 20％ 0％ F1

[0058] result

[0059] The examples were tested using the test methods listed above. The results are shown in Tables 3 to 6.

[0060] Table 3. Optical transmittance, haze, clarity, and color shift results

[0061] Example No. Transmittance (%) Haze (%) transparency(%) ΔE* C0 95.1 0.7 100.0 0.38 C1 94.5 0.6 100.0 0.67 C2 94.2 42.6 61.7 0.96 E1 92.8 2.4 100.0 0.69

[0062] Table 4. Microcombustion calorimetry (MCC) results

[0063]

[0064] Table 5. Peel Adhesion Results

[0065]

[0066] *(23°C and 50% relative humidity); NA indicates the sample is not easy to test

[0067] Table 6.DSC results

[0068] Example There is endothermic C1 no C2 yes E1 no

[0069] Thus, various embodiments of flame retardant adhesives for films are disclosed.Other features and combinations of features within the scope of the present disclosure may be apparent to those skilled in the art having the benefit of the drawings, detailed description, and claims.

[0070] Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as modified by the terms "exactly" or "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and the appended claims are approximations that may vary depending upon the desired properties sought to be obtained by one skilled in the art utilizing the teachings disclosed herein or, for example, within typical ranges of experimental error.

[0071] The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (eg, 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range.

[0072] The singular forms "a," "an," and "the" encompass embodiments having plural referents, unless the context clearly dictates otherwise.

[0073] The phrases "at least one of," "comprising at least one of," and "one or more of" following a list refer to any one of the items in the list and any combination of two or more items in the list.

Claims

1. A membrane comprising: basal layer; as well as An adhesive layer is provided on the base layer, wherein the adhesive layer comprises an adhesive polymer, a polyphosphonate and an organic phosphate. 2 . The film of claim 1 , wherein the adhesive layer has a haze % less than or equal to 3%.

3. The film of claim 1 or 2, wherein the adhesive layer has a peel adhesion greater than or equal to 700 N / m when laminated to a polymer or metal substrate.

4. The film of claim 3, wherein the adhesive layer has a peel adhesion greater than the peel adhesion of an adhesive layer comprising the adhesive polymer without the polyphosphonate and the organophosphate when laminated to a polymeric or metallic substrate.

5. The film of any one of claims 1 to 4, wherein the polymer or metal substrate has a vinyl or aluminum surface.

6. The film of any one of claims 1 to 5, wherein the adhesive polymer comprises polymer chains formed by reacting one or more acrylates.

7. The film of claim 6, wherein the polymer chains are formed by reacting at least one acrylate having an alkyl ester group with a longest carbon chain length of less than or equal to 4.

8. The film of claim 6 or 7, wherein the polymer chains are formed by reacting acrylic acid.

9. The film of any one of claims 6 to 8, wherein the polymer chains are formed by reacting 2-ethylhexyl acrylate.

10. The film of any one of claims 1 to 9, wherein the adhesive layer comprises polyphosphonate and organophosphate in an amount of at least 20% by weight of the adhesive layer.

11. The membrane of any one of claims 1 to 10, wherein the polyphosphonate comprises oligomers having a molecular weight greater than 7000 and a polydispersity index less than 4.

12. The membrane of any one of claims 1 to 11, wherein the polyphosphonate is a non-cyclic polymer.

13. The membrane of any one of claims 1 to 12, wherein the polyphosphonate is free of alcohol functional groups.

14. The film of any one of claims 1 to 13, wherein the adhesive layer has no melting endotherm above 393K.

15. The film of any one of claims 1 to 14, wherein the substrate layer is transparent.

16. The film of any one of claims 1 to 15, wherein the adhesive layer is colorless.

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