Flame-retardant pressure-sensitive adhesive and its preparation method

Abstract

A method for preparing a (meth)acrylate copolymer having phosphate ester side groups and a pressure-sensitive adhesive comprising the (meth)acrylate copolymer having phosphate ester side groups are provided. The method includes reacting a precursor (meth)acrylate copolymer having carboxylic acid side groups with an epoxy-functionalized phosphate ester compound. The phosphate ester side groups on the reaction product can be used as flame retardants in the pressure-sensitive adhesive.

Description

Background Technology

[0001] Polymer materials, such as pressure-sensitive adhesives, are used in a variety of applications where fire risk is a concern, including aircraft, automobiles, trains, ships, building construction, and applications involving electronic and electrical wiring. Because many polymer materials are flammable, various flame retardants are added to minimize the fire risk associated with their use. Flame retardants reduce the flammability of various materials through a number of mechanisms, such as quenching free radicals in the gas phase, reacting with chemical fragments from the burning material to initiate char formation, or forming a barrier layer within the burning material.

[0002] Commonly used flame retardants include halogenated compounds, such as polyhalogenated diphenyl ethers. These flame retardants are well-known and highly effective at retarding the flames of combustible materials. However, many compounds in this class of flame retardants are considered hazardous substances. Since July 1, 2006, several of the most effective halogenated flame retardants have been banned by the European Union under the Restriction of Hazardous Substances Directive (RoHS). Other countries and individual states in the United States have also implemented similar RoHS directives.

[0003] Phosphorus-based compounds are a major class of non-halogenated flame retardants that have been used to replace halogenated flame retardants in many applications. Ammonium polyphosphate (APP) is the most effective non-halogenated flame retardant; however, they have limited compatibility with polymeric materials such as pressure-sensitive adhesives. For example, to function effectively as a flame retardant, the amount added often tends to result in poor adhesion, reduced shear retention, and poor processability.

[0004] Metal hydroxides, zinc borate, and melamine particles are also effective non-halogenated flame retardants, but they must be added at high loading levels to pass standard flammability tests, which can result in poor adhesion and poor mechanical properties. Summary of the Invention

[0005] A method for preparing a (meth)acrylate copolymer having phosphate ester side groups is provided, as well as a pressure-sensitive adhesive comprising the (meth)acrylate copolymer having phosphate ester side groups. The phosphate ester side groups can act as flame retardants.

[0006] In a first aspect, a method is provided for preparing a (meth)acrylate copolymer having phosphate-containing side groups. The method includes providing a precursor (meth)acrylate copolymer containing carboxylic acid side groups, and forming a reaction mixture comprising the precursor (meth)acrylate copolymer and an epoxy-functionalized phosphate compound. The method further includes reacting the epoxy groups of the epoxy-functionalized phosphate compound with the carboxylic acid side groups of the precursor (meth)acrylate copolymer to form a (meth)acrylate copolymer having phosphate-containing side groups.

[0007] In a second aspect, a pressure-sensitive adhesive prepared according to the method described in the first aspect above is provided.

[0008] In a third aspect, an article is provided comprising (a) a permanent or temporary substrate and (b) a pressure-sensitive adhesive described in the second aspect above positioned adjacent to the permanent or temporary substrate.

[0009] According to the Pressure-Sensitive Tape Council, pressure-sensitive adhesives (PSAs) are defined as having the following properties: (1) strong and permanent initial tack, (2) adhesion with light finger pressure, (3) sufficient ability to remain on the adhesive, and (4) sufficient cohesive strength for clean removal from the adhesive. Materials found to function effectively as PSAs include polymers designed and formulated to exhibit the desired viscoelastic properties, achieving a balance between the required initial tack, peel adhesion, and shear retention. PSAs are characterized by being tacky typically at room temperature (e.g., 20°C). Materials that are merely tacky or adhered to a surface do not constitute a PSA; the term PSA encompasses materials with additional viscoelastic properties.

[0010] PSA is an adhesive that meets the Dahlquist standard for tackiness at room temperature and typically exhibits adhesion, cohesion, compliance, and elasticity at room temperature. As described in the "Handbook of Pressure Sensitive Adhesive Technology" (edited by Donatas Satas, 2nd edition, p. 172, Van Nostrand Reinhold, New York, NY, 1989), this standard defines pressure-sensitive adhesives as having a strength greater than 1 × 10⁻⁶. -6 centimeter 2 / Dyne's 1-second creep compliance adhesive. Alternatively, since the modulus is approximately the reciprocal of the creep compliance, pressure-sensitive adhesives can be defined as having a Young's modulus of less than 1 × 10⁻⁶. 6 dynes / cm 2 Adhesive.

[0011] In this application, terms such as “a,” “an,” and “the” are not intended to refer to a single entity but to include general categories, with specific examples provided for illustration.

[0012] The term "and / or" refers to one or both. For example, the expression A and / or B means A alone, B alone, or both A and B.

[0013] The terms "polymer" and "polymer material" are used interchangeably and can refer to homopolymers, copolymers, terpolymers, etc. The term "copolymer" as used refers to a polymer having at least two monomer units of different types.

[0014] As used herein, the term “monomer” refers to a polymerizable compound having an olefinic unsaturated group such as a (meth)acryloyl group or a vinyl group.

[0015] The term "monomer unit" refers to a unit in a polymer that is derived from a monomer contained in a polymerizable composition used to form the polymer. For example, the monomer unit corresponding to the monomer acrylic acid (CH₂=CH-(C=O)-OH) is...

[0016]

[0017] Each asterisk ( * This indicates the attachment sight to another monomer unit or terminal group of the polymer.

[0018] As used herein, the term "side group" refers to a group attached to the carbon-carbon backbone of a (meth)acrylate copolymer. Carboxylic acid side groups may optionally contain groups other than a carboxylic acid group (-(C=O-OH or its salt)). Similarly, phosphate side groups may contain (and often do contain) groups other than a phosphate ester group.

[0019] The term "(meth)acrylate" refers to acrylates and / or methacrylates, and the term "(meth)acrylic acid" refers to acrylic acid and / or (meth)acrylic acid.

[0020] As used herein, the terms “first (meth)acrylate copolymer having carboxylic acid side groups”, “first (meth)acrylate copolymer”, “precursor (meth)acrylate copolymer having carboxylic acid side groups”, “precursor (meth)acrylate copolymer” and similar expressions are used interchangeably.

[0021] As used herein, the terms “second (meth)acrylate copolymer”, “(meth)acrylate copolymer having phosphate ester side groups” and other similar expressions are used interchangeably.

[0022] As used herein, the term "phosphate group" refers to a group containing a group of formula A.

[0023]

[0024] In formula A, group R 3 It is a C1-C4 alkyl, benzyl, or related to R 4The combination forms a cyclic group having 5 or 6 ring members, which may optionally be substituted with at least one C1-C3 alkyl group. Group R 4 It is a C1-C4 alkyl, benzyl, or related to R 3 The combination forms a cyclic group having 5 or 6 ring members that may optionally be substituted with at least one C1-C3 alkyl group.

[0025] The term "C1-C4" refers to groups containing one to four carbon atoms. Similar expressions with other numbers also indicate the number of carbon atoms in the group.

[0026] The term "alkyl" refers to a monovalent group that is an alkane group and includes straight-chain, branched, cyclic, and bicyclic groups, as well as combinations thereof. Unless otherwise specified, alkyl groups typically contain 1 to 20 carbon atoms. In some embodiments, the alkyl group contains 1 to 10 carbon atoms, 2 to 10 carbon atoms, 1 to 6 carbon atoms, 2 to 6 carbon atoms, 1 to 4 carbon atoms, or 2 to 4 carbon atoms. Cyclic alkyl groups and branched alkyl groups have at least three carbon atoms. Examples of "alkyl" groups include, but are not limited to, methyl, ethyl, n-propyl, n-butyl, n-pentyl, isobutyl, tert-butyl, isopropyl, n-octyl, n-heptyl, ethylhexyl, cyclopentyl, cyclohexyl, cycloheptyl, isooctyl, isobornyl, adamantyl, norbornyl, and the like.

[0027] The term "alkanediol" refers to a divalent radical of an alkane and includes straight-chain groups, branched groups, cyclic groups, bicyclic groups, or combinations thereof. Unless otherwise specified, alkanediol groups typically have 1 to 20 carbon atoms. In some embodiments, alkanediol groups have 1 to 10 carbon atoms, 2 to 10 carbon atoms, 1 to 6 carbon atoms, 2 to 6 carbon atoms, 1 to 4 carbon atoms, or 2 to 4 carbon atoms. Cyclic alkanediol groups and branched alkanediol groups have at least 3 carbon atoms. Suitable alkanediol groups include, for example, methyl, ethyl, propanediol, 1,4-butyl, 1,4-cyclohexyl, and 1,4-cyclohexyldimethyl alkylene.

[0028] The term "ether group" refers to an alkyl-oxo-alkyl group.

[0029] The terms “comprising,” “containing,” “including,” and variations thereof, when used in the specification and claims, are not restrictive. Such terms are to be understood as implying inclusion of the stated steps or elements or groups of steps or elements, but not excluding any other steps or elements or groups of steps or elements. The phrase “consisting of…” means including and limited to what follows the phrase “consisting of…”. Therefore, the phrase “consisting of…” indicates that the listed elements are required or mandatory, and that no other elements may be present. The phrase “substantially constitutes…” means including any elements listed after this phrase, and is limited to other elements that do not interfere with or contribute to the activity or effect specified in this disclosure for the listed elements. Therefore, the phrase “substantially constitutes…” indicates that the listed elements are required or mandatory, but other elements are optional and may or may not be present depending on whether they substantially affect the activity or effect of the listed elements. Any element or combination of elements listed in this specification in open language (e.g., including, comprising, containing and their derivatives) is considered to be listed in closed language (e.g., consisting of and their derivatives) and in partially closed language (e.g., substantially consisting of and their derivatives).

[0030] Furthermore, the numerical ranges listed by endpoints include all numbers contained within the range, as well as endpoint values ​​(e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.) and any subranges (e.g., 1 to 5 includes 1 to 4, 1 to 3, 2 to 4, etc.).

[0031] As used in this article, the term "room temperature" refers to a temperature between 20°C and 25°C or between 22°C and 25°C.

[0032] The terms “in the range” or “within the scope” (and similar expressions) include the endpoints of the range. Detailed Implementation

[0033] A method for preparing a (meth)acrylate copolymer having at least one phosphate ester side group and a pressure-sensitive adhesive composition comprising such a copolymer are provided. The phosphate ester side group can act as a flame retardant. Because the phosphate ester side group is covalently bonded to the (meth)acrylate copolymer, it does not leach out over time as is characteristic of many known phosphorus-containing flame retardants.

[0034] A (meth)acrylate copolymer with phosphate ester side groups is formed from a first (meth)acrylate copolymer (i.e., a precursor (meth)acrylate copolymer) with carboxylic acid side groups. The first (meth)acrylate copolymer is then reacted with an epoxy-functionalized phosphate compound. More specifically, the carboxylic acid side groups of the first (meth)acrylate copolymer can ring-open the epoxy groups of the epoxy-functionalized phosphate compound, resulting in the formation of a second (meth)acrylate copolymer with phosphate ester side groups. The phosphate ester groups are covalently linked to the second (meth)acrylate copolymer. The reaction between the carboxylic acid groups of the precursor (meth)acrylate copolymer and the epoxy-functionalized phosphate compound is often highly efficient, with minimal byproduct formation.

[0035] This method of forming (meth)acrylate copolymers with phosphate-containing side groups offers many advantages over other known methods of introducing phosphorus-containing side groups into polymer materials. For example, the preparation of phosphorus-containing monomers can be challenging, and polymerizing other monomers in the presence of phosphorus-containing monomers can produce polymer materials with lower molecular weights than desired. That is, phosphorus-containing monomers can interfere with the free radical polymerization process.

[0036] The epoxy-functionalized phosphate ester compound, the precursor (meth)acrylate copolymer having a carboxylic acid side group, the method for forming the (meth)acrylate copolymer having a phosphate ester side group, and the (meth)acrylate copolymer having a phosphate ester side group are each further described below.

[0037] Epoxy-functionalized phosphate compounds

[0038] Epoxy-functionalized phosphate compounds typically have a single epoxy group (epoxyethylene group) and at least one phosphate group. Any known epoxy-functionalized phosphate compound can be used. The number of phosphate groups in an epoxy-functionalized phosphate compound is typically one, two, or three, although a higher number may be desired. When reacting with epoxy-functionalized phosphate compounds, a single epoxy group is generally preferred to avoid crosslinking reactions of the precursor (meth)acrylate copolymer.

[0039] Suitable epoxy-functionalized phosphate compounds typically have formula (I).

[0040]

[0041] In formula (I), group R 1 It is either hydrogen or methyl. The radical R... 2 It is a C1-C8 alkylene group or a C3-C8 ether group. Group R 3 It is a C1-C4 alkyl, benzyl, or related to R 4This combination forms a cyclic group having 5 or 6 ring members, which can be optionally substituted with C1-C3 alkyl groups. Group R 4 It is a C1-C4 alkyl, benzyl, or related to R 3 They combine to form cyclic groups having 5 or 6 ring members that can be optionally substituted with C1-C3 alkyl groups.

[0042] Some specific epoxy-functionalized phosphate compounds of formula (I) have formula (IA).

[0043]

[0044] In formula (IA), the group R of formula (I) 1 It is hydrogen and the group R of formula (I) 2 It is a methyl subunit. Group R 3 and R 4 Same as defined for equation (I).

[0045] Examples of epoxy-functionalized compounds of formula (IA) include, but are not limited to, phosphoric acid, dimethyl ethylene oxide methyl ester, wherein R 3 and R 4 All are methyl; phosphoric acid, diethyl ethylene oxide methyl ester, wherein R 3 and R 4 All are ethyl; phosphoric acid, dipropyl ethylene oxide methyl ester, wherein R 3 and R 4 All are propyl; phosphoric acid, ethyl methyl dimethyl ethylene oxide methyl ester, wherein R 3 It is methyl and R 4 It is ethyl; phosphoric acid, bis(1-methylethyl)epoxyethylene methyl ester, wherein R 3 and R 4 All are isopropyl; 1,3,2-dioxaphosphacyclopentane, 2-(2-epoxyethylenemethoxy)-, 2-oxide, wherein R 3 and R 4 The combination forms a 5-membered ring; 1,3,2-dioxaphosphazenecyclopentane, 4,5-dimethyl-2-(2-epoxyethylmethoxy)-,2-oxide, wherein R 3 and R 4 The combination forms a 5-membered ring with two methyl groups substituted on adjacent carbon atoms; 1,3,2-dioxaphosphacyclohexane, 2-(2-epoxyethoxymethoxy)-, 2-oxide, wherein R 3 and R 4 Combined to form a 6-membered ring); 1,3,2-dioxaphosphacyclohexane, 5,5-dimethyl-2-(2-epoxyethylmethoxy)-,2-oxide, wherein R 3 and R 4The combination forms a 6-membered ring on the same carbon atom, substituted by two alkyl groups; and phosphate, ethylene oxide methyl bis(phenylmethyl) ester, wherein R 3 and R 4 They are all benzyl groups.

[0046] Other epoxy-functionalized compounds of formula (I) have formula (IB).

[0047]

[0048] In formula (IB), group R 1 It is hydrogen or a C1-C3 alkyl group as described with respect to formula (I). In formula (IB), the group -CH(R) 5 )-CH(R 6 In )-, R 5 It is hydrogen or C1-C3 alkyl and R 6 It is a C1-C3 alkyl group.

[0049] This group corresponds to group R in formula (I). 2 The choice of the alkylidene group. The group R in formula (IB) 7 and R 8 Each of them is a group R in formula (I) 3 and R 4 A subset of, where R in equation (IB) 7 and R 8 Each is a C1-C3 alkyl group.

[0050] Examples of epoxy-functionalized compounds of formula (IB) include, but are not limited to, xylitol, 1,2-dehydro-3,5-dideoxy-3-methyl-,diethyl phosphate, wherein R 1 It is hydrogen, R 5 It is methyl, R 6 It is methyl, R 7 It is ethyl, and R 8 It is ethyl; phosphoric acid, diethyl-1-[(3-methylepoxyethylene)methyl]propyl ester, wherein R 1 It is methyl, R 5 It is hydrogen, R 6 It is propyl, R 7 It is ethyl, and R 8 It is ethyl; and pentitol, 1,2-dehydro-3,5-dideoxy-,4-(diethyl phosphate), wherein R 1 It is hydrogen, R 5 It is hydrogen, R 6 It is methyl, R 7 It is ethyl, and R 8 It is an ethyl group.

[0051] Other epoxy-functionalized compounds of formula (I) also have formula (IC).

[0052]

[0053] In formula (IC), group R 9 It is hydrogen or C1-C3 alkyl, and the group in formula (IC) is -CH2-O-CH(R) 9 )-CH2- corresponds to R in equation (I) 2 The selection of C3-C8 ether groups. Each group R in formula (IC) 10 and R 11 It is a C1-C3 alkyl group, which corresponds to the group R in formula (I). 3 and R 4 A subset of.

[0054] Examples of epoxy-functionalized compounds of formula (IC) include, but are not limited to, CAS number 2620837-91-2, where R 9 R 10 and R 11 Each is methyl; and CAS number 2620837-90-2, where R 9 It is hydrogen, R 10 It is methyl, and R 11 It is a methyl group.

[0055] Other epoxy-functionalized compounds have formula (II).

[0056]

[0057] In equation (II), R 12 It is an alkyl subunit with 1 to 2 carbon atoms, R 13 It is an alkyl subunit with 2 to 4 carbon atoms, R 14 It is a C1-C4 alkyl group or related to R 15 The combination forms a cyclic group having 5 or 6 ring members, optionally substituted with C1-C3 alkyl groups, and R 15 It is a C1-C4 alkyl group or related to R 14 The combination forms a cyclic group having 5 or 6 ring members, optionally substituted with C1-C3 alkyl groups. The structure shown in formula (II) is a cation, and an anion associated with the cation is present, which is not shown in the formula. The anion is typically a halide, but other anions may also be present.

[0058] Examples of formula (II) are 2-(ethylene oxide methane ammonium) and N,N,N-tris(2-hydroxyethyl phosphate diethyl ester), as shown below.

[0059]

[0060] This compound has formula (II), where R... 12 For subunit A, R 13 For subunit A, R 14 It is ethyl, and R 15 It is an ethyl group.

[0061] In many embodiments, the epoxy-functionalized phosphate ester compound has formula (I). In some applications requiring high adhesive strength, when used as a pressure-sensitive adhesive, the salts of those such as formula (II) can adversely affect the adhesive properties of the second (meth)acrylate copolymer. However, in some embodiments, the epoxy-functionalized phosphate ester compound has formula (II) and is advantageously used due to its higher phosphate ester content, which can promote improved flame retardancy.

[0062] Precursor (meth)acrylate copolymers containing carboxylic acid side groups

[0063] The precursor (meth)acrylate copolymer has carboxylic acid-containing side groups that can react with epoxy-functionalized phosphate compounds. Any suitable monomer having carboxylic acid-containing groups may be included in the monomer mixture used to form the precursor (meth)acrylate copolymer.

[0064] Examples of monomers containing a carboxylic acid group include, but are not limited to, acrylic acid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid, citraconic acid, maleic acid, oleic acid, and 2-carboxyethyl (meth)acrylate. In most embodiments, the monomer containing a carboxylic acid group is acrylic acid, methacrylic acid, or a mixture thereof.

[0065] Based on the total weight of the monomers in the monomer mixture used to form the precursor (meth)acrylate copolymer, the monomer having a carboxylic acid group may be present in an amount ranging from 0.1 wt% to 25 wt%. Similarly, based on the total weight of the precursor (meth)acrylate copolymer, the precursor (meth)acrylate copolymer comprises 0.1 wt% to 25 wt% of monomer units having carboxylic acid side groups. This amount may be at least 0.1 wt%, at least 0.2 wt%, at least 0.3 wt%, at least 0.5 wt%, at least 1 wt%, at least 2 wt%, at least 3 wt%, at least 5 wt%, at least 10 wt%, at least 15 wt%, or at least 20 wt%, and at most 25 wt%, at most 20 wt%, at most 15 wt%, at most 10 wt%, or at most 5 wt%. Based on the total weight of the precursor (meth)acrylate copolymer and / or based on the total weight of the monomers in the monomer mixture, the range can be, for example, 0.1 wt% to 20 wt%, 1 wt% to 20 wt%, 0.1 wt% to 15 wt%, 1 wt% to 15 wt%, 0.1 wt% to 10 wt%, 1 wt% to 10 wt%.

[0066] Typically, a precursor (meth)acrylate is chosen as the pressure-sensitive adhesive, so that the resulting (meth)acrylate copolymer with phosphate ester side groups will also be a pressure-sensitive adhesive. That is, monomers are selected to form a precursor (meth)acrylate copolymer that serves as the elastomer material. The glass transition temperature (Tg) of the elastomer material is typically not greater than 20°C, not greater than 10°C, not greater than 0°C, not greater than -10°C, not greater than -20°C, not greater than -30°C, not greater than -40°C, or not greater than -50°C. The glass transition temperature can be measured using techniques such as differential scanning calorimetry and dynamic mechanical analysis. Alternatively, the Fox equation can be used to estimate the glass transition temperature. Lists of glass transition temperatures for homopolymers are available from various monomer suppliers, such as BASF Corporation (Houston, TX, USA), Polyscience, Inc. (Warrington, PA, USA), and Aldrich (Saint Louis, Missouri, USA), as well as various publications, such as Mattioni et al., *Journal of Chem. Inf. Comput. Sci.*, 2002, 42, 232-240.

[0067] To form elastomer precursor (meth)acrylate copolymers, the monomer composition typically contains at least one low-Tg monomer. As used herein, the term "low-Tg monomer" refers to a monomer whose Tg is not greater than 20°C when homopolymerized (i.e., the homopolymer formed from a low-Tg monomer has a Tg not greater than 20°C). Suitable low-Tg monomers are often selected from alkyl (meth)acrylates, heteroalkyl (meth)acrylates, aryl-substituted alkyl acrylates, and aryloxy-substituted alkyl acrylates.

[0068] Exemplary low-Tg (meth)acrylate alkyl monomers are typically non-tertiary alkyl acrylates, but can be alkyl methacrylates with a straight-chain alkyl group having at least 4 carbon atoms. Specific examples of (meth)acrylate alkyl monomers include, but are not limited to, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, sec-butyl acrylate, n-pentyl acrylate, 2-methylbutyl acrylate, n-hexyl acrylate, cyclohexyl acrylate, 4-methyl-2-pentyl acrylate, 2-methylhexyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, 2-octyl acrylate, isooctyl acrylate, isononyl acrylate, isoamyl acrylate, n-decyl acrylate, isodecyl acrylate, n-decyl methacrylate, lauryl acrylate, isotriadecyl acrylate, n-octadecyl acrylate, isostearyl acrylate, and n-dodecyl acrylate.

[0069] Exemplary low-Tg (meth)acrylate heteroalkyl ester monomers typically have at least 3, at least 4, or at least 6 carbon atoms, and may have up to 30 or more, up to 20, up to 18, up to 16, up to 12, or up to 10 carbon atoms. Specific examples of (meth)acrylate heteroalkyl esters include, but are not limited to, 2-ethoxyethyl acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, 2-methoxyethyl (meth)acrylate, and tetrahydrofuran (meth)acrylate.

[0070] Exemplary aryl-substituted alkyl acrylates or aryloxy-substituted alkyl acrylates include, but are not limited to, 2-diphenylhexyl acrylate, benzyl acrylate, 2-phenoxyethyl acrylate, and 2-phenylethyl acrylate.

[0071] Based on the total weight of the monomers in the monomer mixture used to form the precursor (meth)acrylate copolymer, the monomer mixture used to form the precursor (meth)acrylate copolymer typically contains at least 40% by weight of low-Tg monomers. In some embodiments, the monomer mixture contains at least 45% by weight, at least 50% by weight, at least 60% by weight, at least 65% by weight, at least 70% by weight, at least 75% by weight, or at least 80% by weight, and at most 99.9% by weight, at most 99% by weight, at most 98% by weight, at most 95% by weight, at most 90% by weight, at most 85% by weight, at most 80% by weight, or at most 75% by weight of low-Tg monomers.

[0072] The monomer mixture used to form the precursor may optionally contain high-Tg monomers. As used herein, the term "high-Tg monomer" refers to a monomer having a Tg greater than 30°C, greater than 40°C, or greater than 50°C when homopolymerized (i.e., the homopolymer formed from the monomer has a Tg greater than 30°C, greater than 40°C, or greater than 50°C). Some suitable high-Tg monomers have a single (meth)acryloyl group, such as, for example, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, stearyl methacrylate, phenyl acrylate, benzyl methacrylate, 3,3,5-trimethylcyclohexyl methacrylate, 2-phenoxyethyl methacrylate, N-octyl (meth)acrylamide, and mixtures thereof. Other suitable high-Tg monomers have a single vinyl group that is not a (meth)acryloyl group, such as, for example, various vinyl ethers (e.g., vinyl methyl ether), vinyl esters (e.g., vinyl acetate and vinyl propionate), styrene, substituted styrene (e.g., α-methylstyrene), vinyl halides, and mixtures thereof. Vinyl monomers having the group characteristics of polar monomers are considered polar monomers herein.

[0073] The amount of high-Tg monomers can be up to 50% by weight or even higher, provided that the Tg of the (meth)acrylate copolymer is not greater than 20°C. In some embodiments, this amount can be up to 40% by weight, up to 30% by weight, up to 20% by weight, up to 15% by weight, or up to 10% by weight. The amount can be at least 0.1% by weight, at least 0.5% by weight, at least 1% by weight, at least 2% by weight, or at least 5% by weight. For example, the amount can be in the range of 0% to 50% by weight, 0% to 40% by weight, 0% to 30% by weight, 0% to 20% by weight, 0% to 10% by weight, 1% to 30% by weight, 1% to 20% by weight, or 1% to 10% by weight. The values ​​are based on the total weight of the monomers in the monomer mixture used to form the precursor (meth)acrylate copolymer.

[0074] In addition to monomers containing carboxylic acid groups, monomer mixtures may also contain other polar monomers. Non-acidic polar groups can be hydroxyl, primary amide, secondary amide, tertiary amide, amino, or ether groups. The presence of polar groups facilitates the adhesion of pressure-sensitive adhesives to a variety of substrates. Polar groups are generally not epoxy groups that can react with carboxylic acid side groups to crosslink the precursor (meth)acrylate copolymer.

[0075] Exemplary polar monomers having hydroxyl groups include, but are not limited to: hydroxyalkyl (meth)acrylates (e.g., 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate), hydroxyalkyl (meth)acrylamides (e.g., 2-hydroxyethyl (meth)acrylamides or 3-hydroxypropyl (meth)acrylamides), ethoxylated hydroxyethyl (meth)acrylates (e.g., monomers commercially available from Sartomer (Exton, PA, USA) under the trade names CD570, CD571, and CD572), and aryloxy-substituted hydroxyalkyl (meth)acrylates (e.g., 2-hydroxy-2-phenoxypropyl (meth)acrylate).

[0076] Exemplary polar monomers having a primary amide group include (meth)acrylamide. Exemplary polar monomers having a secondary amide group include, but are not limited to, N-alkyl (meth)acrylamides, such as N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-isopropyl (meth)acrylamide, N-tert-octyl (meth)acrylamide, or N-octyl (meth)acrylamide. Exemplary polar monomers having a tert-amide group include, but are not limited to, N-vinylcaprolactam, N-vinyl-2-pyrrolidone, (meth)acryloylmorpholine, and N,N-dialkyl (meth)acrylamides, such as N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N,N-dipropyl (meth)acrylamide, and N,N-dibutyl (meth)acrylamide.

[0077] Polar monomers having an amino group include various N,N-dialkylaminoalkyl esters and N,N-dialkylaminoalkyl (meth)acrylamides. Examples include, but are not limited to: N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylamide, N,N-dimethylaminopropyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide, N,N-diethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylamide, N,N-diethylaminopropyl (meth)acrylamide, and N,N-diethylaminopropyl (meth)acrylamide.

[0078] Polar monomers with ether linkages include those containing poly(olefin oxide) segments, such as poly(ethylene oxide) (meth)acrylate, poly(propylene oxide) (meth)acrylate, poly(tetramethyl methacrylate) (tetramethyl methacrylate), di(ethylene glycol) ethyl ether (meth)acrylate, etc. Monomers of any suitable molecular weight can be used.

[0079] Based on the weight of the monomers in the monomer mixture used to form the precursor (meth)acrylate copolymer, the amount of optional non-acidic polar monomers is typically in the range of 0% to 15% by weight. If present, the amount of non-acidic polar monomers in the monomer mixture is typically at least 0.1%, 0.2%, 0.5%, or 1% by weight, based on the total weight of the monomers in the monomer mixture. This amount can be up to 15%, 10%, or 5% by weight. For example, based on the total weight of the monomers in the monomer mixture, this amount is typically in the range of 0% to 15%, 0.1% to 10%, 0.5% to 5%, or 1% to 5% by weight.

[0080] In general, the precursor (meth)acrylate copolymer can be formed from a monomer mixture comprising 0.1 wt% to 25 wt% of a monomer having a carboxylic acid group, 40 wt% to 99.9 wt% of a low-Tg monomer, 0 wt% to 50 wt% of a high-Tg monomer, and 0 wt% to 15 wt% of a non-acidic polar monomer. In other embodiments, the monomer mixture comprises 1 wt% to 20 wt% of a monomer having a carboxylic acid group, 50 wt% to 99 wt% of a low-Tg monomer, 0 wt% to 40 wt% of a high-Tg monomer, and 0 wt% to 10 wt% of a non-acidic polar monomer. In yet another embodiment, the monomer mixture comprises 5 wt% to 20 wt% of a monomer having a carboxylic acid group, 50 wt% to 95 wt% of a low-Tg monomer, 0 wt% to 30 wt% of a high-Tg monomer, and 0 wt% to 10 wt% of a non-acidic polar monomer. In other embodiments, the monomer mixture comprises 5% to 15% by weight of a monomer having a carboxylic acid group, 60% to 95% by weight of a low-Tg monomer, 0% to 20% by weight of a high-Tg monomer, and 0% to 10% by weight of a non-acidic polar monomer. The total of all monomers is 100% by weight.

[0081] When (meth)acrylate copolymers are crosslinked, the weight-average molecular weight of the (meth)acrylate copolymer is typically in the range of 10,000 Da to 1,000,000 Da or even higher. For example, the weight-average molecular weight may be at least 20,000 Da, at least 30,000 Da, at least 40,000 Da, or at least 50,000 Da, and may be at most 1,000,000 Da, at most 900,000 Da, at most 800,000 Da, at most 700,000 Da, or at most 600,000 Da.

[0082] Initiators are typically added to monomer mixtures to prepare precursor (meth)acrylate copolymers. The amount of initiator is typically in the range of 0.01% to 1% by weight, based on the total weight of the monomers in the monomer mixture.

[0083] Exemplary thermal initiators include various azo compounds, such as those commercially available under the trade name VAZO from Chemours Co. (Wilmington, DE, USA), including VAZO 67 (which is 2,2'-azobis(2-methylbutyronitrile)), VAZO 64 (which is 2,2'-azobis(isobutyronitrile)), VAZO 52 (which is 2,2'-azobis(2,4-dimethylpentanitrile)), and VAZO 88 (which is 1,1'-azobis(cyclohexanecarboxylonitrile)); various peroxides, such as benzoyl peroxide, cyclohexane peroxide, lauroyl peroxide, di-tert-amyl peroxide, tert-butyl peroxide, dicumyl peroxide, and LUPERSOL from Atofina Chemical. Peroxides (e.g., LUPERSOL 101, which is 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, and LUPERSOL 130, which is 2,5-dimethyl-2,5-bis(tert-butylperoxy)-3-hexyne) commercially available from Inc. (Philadelphia, PA, USA); various hydroperoxides, such as tert-amyl hydroperoxide and tert-butyl hydroperoxide; and mixtures thereof.

[0084] Some exemplary photoinitiators are benzoin ethers (e.g., benzoin methyl ether or benzoin isopropyl ether) or substituted benzoin ethers (e.g., anisole methyl ether). Other exemplary photoinitiators are substituted acetophenones, such as 2,2-diethoxyacetophenone or 2,2-dimethoxy-2-phenylacetophenone (available under the trade name OMNIRAD 651 from iGM Resins (Charlotte, NC, USA) or under the trade name ESACURE KB-1 from Sartoma (Exton, PA, USA). Other exemplary photoinitiators are substituted α-keto alcohols (such as 2-methyl-2-hydroxyacetophenone), aromatic sulfonyl chlorides (such as 2-naphthalenesulfonyl chloride), and photoactive oximes (such as 1-phenyl-1,2-propanedione-2-(O-ethoxycarbonyl)oxime). Other suitable photoinitiators include, for example: 1-hydroxycyclohexylphenyl ketone (commercially available under the trade name OMNIRAD 184), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (commercially available under the trade name OMNIRAD 819), 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one (commercially available under the trade name OMNIRAD 2959), 2-benzyl-2-dimethylamino-1-(4-morpholinylphenyl)butanone (commercially available under the trade name OMNIRAD 369), 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinylpropane-1-one (commercially available under the trade name OMNIRAD 907), and 2-hydroxy-2-methyl-1-phenylpropane-1-one (commercially available under the trade name DAROCUR 1173 from BASF). (Acquired by Florham Park, NJ, USA) (Corporation acquired).

[0085] Precursor (meth)acrylates are typically prepared in organic solvents so that they can readily react with epoxy-functionalized phosphate compounds after preparation. Suitable solvents include, but are not limited to, methanol, ethanol, isopropanol, tetrahydrofuran, heptane, acetone, methyl ethyl ketone, methyl isobutyl ketone, 1-methoxy-2-propanol, methyl acetate, ethyl acetate, butyl acetate, acetone, toluene, xylene, ethylene glycol alkyl ethers, etc. These solvents can be used alone or as mixtures. The reaction mixture may contain any suitable amount of organic solvent, such as up to 80 wt%, up to 70 wt%, up to 60 wt%, up to 50 wt%, up to 40 wt%, or up to 30 wt% based on the total weight of the reaction mixture.

[0086] (meth)acrylate copolymers with phosphate ester side groups

[0087] A precursor (meth)acrylate copolymer having carboxylic acid side group (i.e., a first (meth)acrylate copolymer) is reacted with an epoxy-functionalized phosphate ester compound to form a second (meth)acrylate copolymer having phosphate ester side group. This reaction is typically carried out in the presence of an organic solvent present during the formation of the precursor (meth)acrylate copolymer. Alternatively, if the precursor (meth)acrylate copolymer is prepared in the absence of or in the presence of a small amount of organic solvent, the organic solvent may be added to the reaction mixture used to form the second (meth)acrylate copolymer having phosphate ester side group. Suitable organic solvents and amounts are the same as those listed above for the preparation of precursor (meth)acrylate copolymers.

[0088] If the precursor (meth)acrylate copolymer has (meth)acrylate monomer units, the monomer groups formed by the reaction of the epoxy-functionalized phosphate ester compound of formula (I) have formula (III) as shown in reaction scheme A.

[0089] Reaction scheme A

[0090]

[0091] In formula (III), group R 20 It is either hydrogen or methyl. The radical R... 1 It is hydrogen or a C1-C3 alkyl group. The radical R... 2 It is a C1-C8 alkylene group or a C3-C8 ether group. Group R 3 It is a C1-C4 alkyl, benzyl, or related to R 4 This combination forms a cyclic group having 5 or 6 ring members, which can be optionally substituted with C1-C3 alkyl groups. Group R 4 It is a C1-C4 alkyl, benzyl, or related to R 3 They combine to form cyclic groups having 5 or 6 ring members that can be optionally substituted with C1-C3 alkyl groups.

[0092] When an epoxy-functionalized phosphate ester compound has formula (IA), the reaction product after reacting with a (meth)acrylic acid monomer unit is a monomer unit of formula (III-A).

[0093]

[0094] In formula (III-A), group R 20 R 3 and R 4 Same as above.

[0095] The side group in formula (III-A) is -(C=O)-O-CH2-CH(OH)-CH2-O-(P=O)(OR 3(OR) 4 Similarly, the side group of the reaction product of the (meth)acrylic acid monomer unit and the epoxy-functionalized phosphate compound of formula (IB) is -(C=O)-O-CHR. 1 -CH(OH)-CHR 5 -CHR 6 -O-(P=O)(OR 7 (OR) 8 Furthermore, the side group of the reaction product with the epoxy-functionalized phosphate ester compound of formula (IC) is -(C=O)-O-CH2-CH(OH)-CH2-O-CHR. 9 -CH2-O-(P=O)(OR 10 (OR) 11 ). Group R 3 R 4 R 5 R 6 R 7 R 8 R 9 R 10 and R 11 Same as above.

[0096] Similarly, if the precursor (meth)acrylate copolymer has (meth)acrylate monomer units, then the monomer units formed by the reaction of the epoxy-functionalized phosphate compound of formula (II) have formula (IV).

[0097]

[0098]

[0099] Group R 20 R 12 R 14 and R 15 Same as above.

[0100] Typically, about 25 mol% to 100 mol% of the monomer units having carboxylic acid groups in the precursor (meth)acrylate copolymer are reacted with an epoxy-functionalized phosphate ester compound to produce a (meth)acrylate copolymer having phosphate ester side groups (i.e., a second (meth)acrylate copolymer). Based on the total molar amount of the monomer units having carboxylic acid side groups in the precursor (meth)acrylate copolymer, the conversion rate of the monomer units having carboxylic acid side groups to the monomer units having phosphate ester side groups is at least 25 mol%, at least 30 mol%, at least 35 mol%, at least 40 mol%, at least 50 mol%, at least 60 mol%, at least 70 mol%, or at least 75 mol%, and may be up to 100 mol%, up to 95 mol%, up to 90 mol%, up to 85 mol%, up to 80 mol%, up to 75 mol%, up to 70 mol%, up to 65 mol%, up to 60 mol%, up to 55 mol%, or up to 50 mol%. Advantageously, at least some monomer units with carboxylic acid side groups can be retained to enhance the adhesion of the pressure-sensitive adhesive composition to a variety of substrates. On the other hand, a higher amount of phosphate ester-containing groups tends to improve the flame-retardant properties of the pressure-sensitive adhesive. These two properties are considered to determine the optimal balance of side groups for a particular application.

[0101] In some embodiments, based on the total weight of the second (meth)acrylate copolymer, the second (meth)acrylate copolymer having phosphate-containing side groups comprises 0.1 wt% to 10 wt% of phosphorus-containing monomer units. This amount may be at least 0.1 wt%, at least 0.2 wt%, at least 0.3 wt%, at least 0.5 wt%, at least 1 wt%, at least 2 wt%, at least 3 wt%, at least 4 wt%, or at least 5 wt%, and at most 10 wt%, at most 9 wt%, at most 8 wt%, at most 7 wt%, at most 6 wt%, at most 5 wt%, at most 4 wt%, at most 3 wt%, or at most 2 wt%.

[0102] In some embodiments, the second (meth)acrylate copolymer having phosphate ester side groups is halogen-free. In these embodiments, the epoxy-functionalized phosphate ester compound is not a chloride salt.

[0103] The second (meth)acrylate compound contains no phosphorus-containing groups other than the phosphate-containing group of formula (A). That is, the second (meth)acrylate copolymer contains no or substantially no hypophosphite groups and phosphonate groups. As used herein, with respect to hypophosphite groups and / or phosphonate groups, the second (meth)acrylate copolymer contains less than 0.1% by weight of monomer units having these phosphorus-containing side groups. This amount is typically less than 0.05% by weight or less than 0.01% by weight based on the total weight of the second (meth)acrylate copolymer.

[0104] Coating composition

[0105] To form a pressure-sensitive adhesive article comprising a second (meth)acrylate copolymer having phosphate ester side groups, a coating composition is positioned adjacent to a substrate. The coating composition typically comprises a second (meth)acrylate copolymer and an organic solvent, such as those described above. These coating compositions can be prepared such that they are transparent to the naked eye.

[0106] In some embodiments, the coating composition also includes an optional tackifier. Available tackifiers include, for example, rosin ester resins, terpene phenol resins, and hydrocarbon resins. The amount of the optional tackifier, based on the solids content of the coating composition, is generally in the range of 0% to 30% by weight. If present, the amount of tackifier, based on the total weight of solids in the coating composition, may be at least 5% by weight, at least 10% by weight, at least 15% by weight, or at least 20% by weight, and at most 40% by weight, at most 35% by weight, at most 30% by weight, at most 25% by weight, or at most 20% by weight.

[0107] Other components typically added to pressure-sensitive adhesives can be included in the coating composition. These components include, for example, antioxidants, fillers, pigments, etc. Any suitable amount can be used, provided that the dried coating composition is a pressure-sensitive adhesive.

[0108] Pressure-sensitive adhesive products

[0109] Coating compositions are typically applied adjacent to a substrate to provide pressure-sensitive adhesive articles. The term "adjacent" means that the coating composition is in contact with the substrate or separated from it by another layer, such as an adhesion-promoting layer. Pressure-sensitive adhesive articles typically include a permanent or temporary base layer.

[0110] Any suitable substrate can be used. For example, the substrate can be flexible or non-flexible and can be formed from polymeric materials, glass or ceramic materials, metals (including various alloys), or combinations thereof. In many embodiments, the substrate is glass, ceramic, or metal. In other embodiments, the substrate is a polymeric material, such as, for example, a polymeric film or plastic composite (e.g., glass or fiber-filled plastic). The polymeric film can be prepared, for example, from polyolefins (e.g., polyethylene, polypropylene, or copolymers thereof), polyurethane, polyvinyl acetate, polyvinyl chloride, polyesters (polyethylene terephthalate or polyethylene naphthalate), polycarbonate, poly(methyl methacrylate) (PMMA), ethylene-vinyl acetate copolymers, polyamides, cellulose materials (e.g., cellulose acetate, cellulose triacetate, and ethyl cellulose), etc. These substrates are permanent substrates because they cannot be easily removed from the pressure-sensitive adhesive composition.

[0111] In some embodiments, the substrate is a temporary substrate, such as a release liner. The function of the temporary substrate is to provide support for the pressure-sensitive adhesive composition until it is applied to a permanent substrate. Such articles are often referred to as transfer tapes. The release liner can be one or both outer surfaces of the pressure-sensitive adhesive layer. Suitable release liners typically have low affinity for pressure-sensitive adhesive curable compositions. Exemplary release liners may be made from paper materials (e.g., kraft paper) or other types of polymeric materials. Some release liners are coated with an outer layer of release agent, such as silicone-containing materials or fluorocarbon-containing materials (e.g., polyfluoroethers or polyvinyl fluoride).

[0112] When the coating composition contains organic solvents, the coating is applied to a substrate, which may be permanent or temporary, and then dried to remove the organic solvents. The drying temperature may be room temperature (e.g., 20 to 25 degrees Celsius) or higher.

[0113] The resulting product may have flame-retardant properties. For example, the product may have a UL94 VTM-0 flammability rating.

[0114] Example

[0115] Unless otherwise stated, all parts, percentages, ratios, etc., in the examples and the remainder of this specification are by weight. Preparation examples are identified by the label prefix "PE", comparative examples by the label prefix "CE", and working examples by the label prefix "EX".

[0116] Unless otherwise specified, all other reagents were obtained or purchased from fine chemical suppliers such as MilliporeSigma, Burlington, MA, USA, or synthesized by known methods. Table 1 (below) lists the materials used in the examples and their sources.

[0117] Table 1

[0118]

[0119] Test methods

[0120] UL94 VTM Flammability Test

[0121] Adhesive samples were laminated between 0.05 mm thick Kapton polyimide films. The laminated sample (the adhesive between the two polyimide films) was approximately 0.25 mm thick. The flammability of these laminated samples was evaluated using the UL94 VTM test developed by UL, LLC (Northbrook, IL, USA), except that the samples were not subjected to any pretreatment. Each sample was wound around a mandrel and then clamped to a holder. In this test, a flame from a Bunsen burner was applied for 3 seconds (s) twice. The second flame application time began as soon as the first burn time ended. The flame height was 20 mm. The possible flammability ratings in the UL94 VTM test are described in Table 2 below.

[0122] Table 2

[0123]

[0124] 90° angle peel adhesion strength test

[0125] Peel adhesion strength at a 90° angle was measured using an IMASS SP-200 slip / peel tester (available from IMASS Inc., Accord, MA, USA) at a peel rate of 305 mm / min (12 in / min). Test panels were prepared by wiping the panel with an isopropyl alcohol (IPA)-moistened paper towel and then pressing the panel firmly by hand 8 to 10 times. This procedure was repeated twice with a clean paper towel moistened with solvent. The cleaned panels were allowed to dry. Adhesive tape was cut into strips measuring 1.27 cm × 20 cm (1 / 2 inch × 8 inches) and then rolled onto the cleaned panel twice using a 2.0 kg (4.5 lb) rubber roller. The prepared samples were stored at 23°C and 50% relative humidity for 24 hours prior to testing. Two samples were tested for each example, and the average value is expressed as N / cm. Record the failure modes and label them as COH (cohesive) (i.e., adhesive residue with cracks on both the strip and the test surface), ADH (adhesive) (i.e., adhesive is cleanly peeled off from the test surface), and / or 2-B (2-adhesive) (adhesive is peeled off from the backing).

[0126] Preparation Example 1: FRRA1

[0127]

[0128] Epoxy-functionalized monophosphate (flame retardant reactive additive 1 or FRRA1) was synthesized by reacting diethyl chlorophosphate with glycidyl phosphate. 20.63 g of diethyl chlorophosphate (0.22 mol), 40.48 g of triethylamine (0.4 mol), and 100 g of toluene were placed in a 250 mL round-bottom flask. The flask was placed in an ice bath (0 °C), and the mixture was stirred with a magnetic stirrer to prepare a homogeneous solution. Then, 14.82 g of glycidyl phosphate (0.2 mol) was added dropwise to the solution over 30 minutes. When the addition was complete, the mixture was allowed to reach room temperature and maintained at room temperature with stirring for 1 day to complete the reaction. After 1 day, the insoluble white solid was removed by simple filtration through a sintered porous funnel (pore size 10 μm to 20 μm). The reaction solvent and unreacted reagents were removed by rotary evaporator under reduced pressure. A pale yellow transparent liquid was obtained.

[0129] Preparation Example PE2:FRRA2

[0130] The synthesis of epoxy-functionalized triphosphate additives (flame retardant additive 2 or FRRA2) is carried out in two main steps. First, tertiary amine-functionalized triphosphates (TATP) are synthesized and isolated as synthetic intermediates. Second, TATP is reacted with epichlorohydrin to obtain FRRA2 as the final product.

[0131]

[0132] The tertiary amine-functionalized triphosphate (TATP) was synthesized as follows. The first step involved reacting diethyl chlorophosphate with triethanolamine. In a 250 mL round-bottom flask, 56.94 g of diethyl chlorophosphate (0.33 mol), 60.71 g of triethylamine (0.6 mol), and 100 g of toluene were placed. The flask was placed in an ice bath (0 °C), and the mixture was stirred with a magnetic stirrer to prepare a homogeneous solution. Then, 14.92 g of triethanolamine (0.1 mol) was added dropwise to the solution over 30 minutes. When the addition was complete, the mixture was allowed to reach room temperature and maintained at room temperature with stirring for 1 day to complete the reaction. After 1 day, the insoluble white solid was removed by simple filtration through a sintered porous funnel (pore size 10 μm to 20 μm). The reaction solvent and unreacted reagents were removed under reduced pressure using a rotary evaporator. TATP was obtained as a pale yellow, transparent liquid.

[0133]

[0134] The following is a method for synthesizing epoxy-functionalized triphosphate additives (flame retardant reactive additive 2 or FRRA2). First, 11.15 g of TATP (0.02 mol) and 1.85 g (0.02 mol) of epichlorohydrin were placed in a 40 mL vial. The vial was placed on a mixing roller and mixed at room temperature for 24 hours. 1H and 13 C10 NMR analysis of the final product (FRRA2) confirmed its chemical structure.

[0135] Preparation Example 3: Precursor Copolymer

[0136] Precursor (meth)acrylate copolymers were prepared by free radical polymerization of two monomers: 2-EHA (186.0 g) and AA (14.0 g). The monomers were mixed with a polymerization solvent (ethyl acetate, 300.0 g) and a thermal free radical initiator (VAZO 67, 0.2 wt%, 0.4 g relative to the total monomers) in an amber narrow-neck pint flask to achieve a monomer concentration of 40.0 wt%. The solution was degassed by purging with nitrogen for 5 minutes at room temperature. The flask was tightly capped and placed in a LAUNDER-O-METER (SDL Atlas USA, Rock Hill, SC, USA) and kept at 60°C for 24 hours. The flask was cooled to room temperature, and the resulting copolymer solution was used in the formulations described in the examples.

[0137] Examples EX1 to EX4 and Comparative Examples CE1 to CE3

[0138] Combine the compositions in Table 3 in 40 mL vials and place them on a mixing roller. Mix the solutions on the roller at room temperature for at least 24 hours. Formulations with reactive additives (FRRA1, FRRA2) showed an increase in viscosity during mixing due to the ring-opening reaction between the precursor (meth)acrylate copolymer and the epoxy-functionalized phosphate compound. All coating solutions were clear and homogeneous.

[0139] Table 3

[0140]

[0141] Coatings were prepared on PET (for adhesion testing) and KAPTON HN (for flammability testing) backings using a square applicator (wet gap thickness: 0.2 mm). The coatings were dried in a convection oven at 70°C for at least 30 minutes. Prior to evaluation, the dried coatings were stored at controlled temperature and humidity (23°C, 50% relative humidity) for at least 24 hours.

[0142] Dry coatings of the materials in Table 3 (those on the KAPTON HN film) were prepared and tested according to the UL94 VTM flammability test procedure. The results are shown in Table 4.

[0143] Table 4

[0144]

[0145] Upon the first application of flame, both the adhesive without flame retardants and the adhesive with non-reactive flame retardants burned to the top. Coatings containing reactive monophosphates and triphosphates rapidly ceased burning before the flame reached the end of the sample. Even on the second application, the flame extinguished within 10 seconds to achieve a VTM0 rating.

[0146] Dry coatings of the materials in Table 3 (those on PET films) were prepared and tested according to the procedure for the 90° angle peel adhesion strength test. The results are shown in Table 5.

[0147] Table 5

[0148]

Claims

1. A method for forming a (meth)acrylate copolymer having phosphate ester side groups, the method comprising: Provides a precursor (meth)acrylate copolymer having monomer units containing carboxylic acid side groups; Forming a reaction mixture comprising the precursor (meth)acrylate copolymer and the epoxy-functionalized phosphate compound; and The epoxy-functionalized phosphate ester compound is reacted with the carboxylic acid side group of the precursor (meth)acrylate copolymer to form the (meth)acrylate copolymer having the phosphate ester side group.

2. The method according to claim 1, wherein the epoxy-functionalized phosphate compound has a single epoxy group and one to three phosphate groups.

3. The method according to claim 1, wherein the epoxy-functionalized phosphate compound has formula (I). in R 1 It is hydrogen or methyl; R 2 It is a C1-C8 alkyl subunit or a C3-C8 ether group; R 3 It is a C1-C4 alkyl, benzyl, or related to R 4 The combination forms a cyclic group having 5 or 6 ring members, optionally substituted with C1-C3 alkyl groups; and R 4 It is a C1-C4 alkyl, benzyl, or related to R 3 They combine to form cyclic groups having 5 or 6 ring members, optionally substituted with C1-C3 alkyl groups.

4. The method according to claim 3, wherein the epoxy-functionalized phosphate compound of formula (I) has formula (IA).

5. The method according to claim 1, wherein the epoxy-functionalized phosphate compound has the formula (IB). in R 1 It is hydrogen or C1-C3 alkyl; R 5 It is hydrogen or C1-C3 alkyl; R 6 It is a C1-C3 alkyl group; R 7 It is a C1-C3 alkyl group; and R 8 It is a C1-C3 alkyl group.

6. The method according to claim 3, wherein the epoxy-functionalized phosphate compound of formula (I) has the formula (IC). in R 9 It is hydrogen or C1-C3 alkyl; R 10 It is a C1-C3 alkyl group; and R 11 It is a C1-C3 alkyl group.

7. The method according to claim 1, wherein the epoxy-functionalized phosphate compound has formula (II). in R 12 It is an alkyl subunit having one to two carbon atoms; R 13 It is an alkyl subunit with 2 to 4 carbon atoms; R 14 It is a C1-C4 alkyl group, or related to R 15 The combination forms a cyclic group having 5 or 6 ring members, optionally substituted with C1-C3 alkyl groups; and R 15 It is a C1-C4 alkyl group, or related to R 14 They combine to form cyclic groups having 5 or 6 ring members, optionally substituted with C1-C3 alkyl groups.

8. The method according to claim 1, claim 4, claim 5 or claim 6, wherein, based on the total weight of the precursor (meth)acrylate, the precursor (meth)acrylate comprises 1% to 20% by weight of monomer units containing the carboxylic acid group.

9. The method of claim 8, wherein at least 50% of the monomer units comprising the carboxylic acid group in the precursor (meth)acrylate react with the epoxy-functionalized phosphate compound.

10. A pressure-sensitive adhesive comprising a (meth)acrylate copolymer having phosphate ester side groups, wherein the (meth)acrylate copolymer having phosphate ester side groups is a reaction product of a reaction mixture, the reaction mixture comprising: a) a precursor (meth)acrylate copolymer having monomer units containing carboxylic acid side groups; and b) An epoxy-functionalized phosphate compound, wherein the epoxy group of the epoxy-functionalized phosphate compound undergoes a ring-opening reaction with the carboxylic acid side group of the precursor (meth)acrylate copolymer.

11. An article of manufacture, said article comprising: Permanent or temporary base; as well as The pressure-sensitive adhesive composition according to claim 10 is positioned adjacent to the permanent or temporary substrate.

12. The article of claim 11, wherein the substrate is a polyimide film, and wherein the article has a flammability rating of UL94 VTM-0.

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