Flame-retardant pressure-sensitive adhesive and manufacturing method

Abstract

A method for producing a (meth)acrylate copolymer having pendant phosphate-containing groups and a pressure-sensitive adhesive containing the (meth)acrylate copolymer having pendant phosphate-containing groups are provided. The method includes reacting a precursor (meth)acrylate copolymer having pendant carboxylic acid groups with an epoxy-functionalized phosphate compound. The phosphate-containing pendant groups on the reaction product can function as a flame retardant for the pressure-sensitive adhesive.

Description

Background Art

[0001] Polymer materials such as pressure-sensitive adhesives (PSAs) are used in various applications where fire risk is a major concern, such as in aircraft, automobiles, trains, ships, building structures, and also with electronic devices and electrical wiring. Since many polymer materials are flammable, various flame retardants are added to minimize the fire risk associated with their use. Flame retardants can reduce the flammability of various materials by various mechanisms, such as quenching free radicals in the gas phase, reacting with chemical fragments of the burning material to initiate char formation, or forming a barrier layer within the burning material.

[0002] Generally used flame retardants include halogenated compounds such as polyhalogenated diphenyl ethers. These flame retardants are well known and can be effective in flame-retarding flammable materials. However, many compounds in this class of flame retardants are regarded as harmful substances. Some of the most effective halogenated flame retardants have been prohibited by the European Union since July 1, 2006, based on the RoHS (Restriction of the Use of Certain Hazardous Substances) directive. Individual states in other countries and the United States also follow similar RoHS directives.

[0003] Phosphorus-based compounds are a major class of non-halogenated flame retardants, which are used to replace halogenated flame retardants in many applications. Ammonium polyphosphate (APP) is one of the most effective non-halogenated flame retardants, but their compatibility with polymer materials such as pressure-sensitive adhesives is limited. For example, in order to function effectively as a flame retardant, the amount added often tends to lead to poor adhesion, reduced shear holding power, and poor processability.

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

Summary of the Invention

[0005] Provided are a method for producing a (meth)acrylate copolymer having a pendant group containing phosphate, and a pressure-sensitive adhesive containing the (meth)acrylate copolymer having a pendant group containing phosphate. The pendant group containing phosphate can function as a flame retardant.

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

[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 that includes (a) a permanent or temporary substrate, and (b) the pressure-sensitive adhesive described in the second aspect disposed 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 characteristics: (1) strong and permanent adhesiveness, (2) adhesion under finger pressure, (3) sufficient holding power to the adherend, and (4) sufficient cohesive strength to peel cleanly from the adherend. Materials that have been found to function well as PSAs include polymers that are designed and formulated to exhibit the necessary viscoelastic properties that provide the desired balance of adhesiveness, peel adhesion, and shear holding power. PSAs are typically characterized by being adhesive at room temperature (e.g., 20 °C). Materials that are merely adhesive or sticky to a surface do not constitute a PSA, and the term PSA encompasses materials with additional viscoelastic properties.

[0010] A PSA is an adhesive that meets the Dahlquist criterion for adhesiveness at room temperature and typically exhibits adhesion, cohesion, compliance, and elasticity at room temperature. This criterion defines a pressure-sensitive adhesive as an adhesive having a 1-second creep compliance greater than 1 x 10 nd cm -6 / dyne as described in "Handbook of Pressure Sensitive Adhesive Technology", Donatas Satas (Ed.), 2 2 Edition, p. 172, Van Nostrand Reinhold, New York, N.Y., 1989. Alternatively, since the modulus of elasticity is approximately the reciprocal of the creep compliance, a pressure-sensitive adhesive may be defined as an adhesive having a Young's modulus of less than 1 x 10 6 dyne / cm 2 .

[0011] In this application, terms such as "a", "an", and "the" are not intended to refer only to singular entities but include general categories for which specific examples may be used for the purposes of explanation.

[0012] The term "and / or" means 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" is used to refer to a polymer having at least two different types of monomer units.

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

[0015] The term "monomer unit" refers to a unit in a polymer 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 as follows,

Chemical formula

[0016] As used herein, the term "pendent" refers to a group bonded to the carbon-carbon backbone chain of a (meth)acrylate copolymer. The pendent carboxylic acid-containing group can optionally contain additional groups in addition to the carboxylic acid group (-(C=O-OH or its salt). Similarly, the pendent group containing phosphate can (typically does) contain other groups in addition to the phosphate group.

[0017] The term "(meth)acrylate" refers to acrylate and / or methacrylate, and the term "(meth)acrylic acid" refers to acrylic acid and / or (meth)acrylic acid.

[0018] As used herein, the terms "first (meth)acrylate copolymer having a pendant carboxylic acid group", "first (meth)acrylate copolymer", "precursor (meth)acrylate copolymer having a pendant carboxylic acid group", "precursor (meth)acrylate copolymer", and similar expressions are used interchangeably.

[0019] As used herein, the terms "second (meth)acrylate copolymer", "(meth)acrylate copolymer having a pendant group containing phosphate", and other similar expressions are used interchangeably.

[0020] As used herein, the term "phosphate-containing group" refers to a group containing a group of Formula A. [Chemical Formula] In Formula A, the group R 3 is C1-C4 alkyl, benzyl, or together with R 4 forms a cyclic group having 5 or 6 ring members, which may be optionally substituted with at least one C1-C3 alkyl. The group R 4 is C1-C4 alkyl, benzyl, or together with R 3 forms a cyclic group having 5 or 6 ring members, which may be optionally substituted with at least one C1-C3 alkyl.

[0021] The term "C1-C4" when referring to a group means that the group contains 1 to 4 carbon atoms. Similar expressions having other numbers likewise indicate the number of carbon atoms in the group.

[0022] The term "alkyl" refers to a monovalent group that is a radical of an alkane and includes straight-chain, branched-chain, cyclic, and bicyclic groups, as well as combinations thereof. Unless otherwise indicated, an alkyl group typically contains from 1 to 20 carbon atoms. In some embodiments, an alkyl group contains from 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-chain alkyl groups have at least 3 carbon atoms. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, n-butyl, n-pentyl, isobutyl, t-butyl, isopropyl, n-octyl, n-heptyl, ethylhexyl, cyclopentyl, cyclohexyl, cycloheptyl, isooctyl, isobornyl, adamantyl, norbornyl, and the like.

[0023] The term "alkylene" refers to a divalent group that is a radical of an alkane and includes linear, branched-chain, cyclic, bicyclic, or combinations thereof groups. Unless otherwise indicated, an alkylene group typically has from 1 to 20 carbon atoms. In some embodiments, an alkylene group has from 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 and branched-chain alkylene groups have at least 3 carbon atoms. Suitable alkylene groups include, for example, methylene, ethylene, propylene, 1,4-butylene, 1,4-cyclohexylene, and 1,4-cyclohexyldimethylene.

[0024] The term "ether group" refers to an alkylene-oxy-alkylene group.

[0025] The terms "comprise", "contain", "include" and variations thereof do not have a limiting meaning where these terms appear in the specification and claims. Such terms are understood to imply that one step or element, or a group of steps or elements, described is included, but do not imply that any other one step or element, or group of steps or elements, is excluded. "Consisting of" means including and limited to whatever is before the phrase "consisting of". Thus, the phrase "consisting of" indicates that the recited elements are necessary or essential and that no other elements can exist. "Consisting essentially of" means including all elements enumerated before this phrase and limited to other elements that do not interfere with or contribute to the action or function specified in this disclosure with respect to these enumerated elements. Thus, the phrase "consisting essentially of" indicates that the recited elements are necessary or essential, but that other elements are optional and may or may not exist depending on whether they substantially affect the action or function of the enumerated elements. Any element or combination of elements described herein in open-ended language (e.g., comprise, include, contain, and their derivatives) is considered to be further described in closed-ended language (e.g., "consisting of" and its derivatives) and partially closed-ended language (e.g., "consisting essentially of" and its derivatives).

[0026] Also, the recitation of a numerical range by endpoints includes all numbers within that range and the endpoints (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.).

[0027] As used herein, the term "room temperature" refers to a temperature of 20°C to 25°C or 22°C to 25°C.

[0028] The term "in the range" or "within a range" (and similar recitations) includes the endpoints of the recited range.

DETAILED DESCRIPTION OF THE INVENTION

[0029] There are provided a method for producing a (meth)acrylate copolymer having a pendant group containing at least one phosphate, and a pressure-sensitive adhesive composition containing this copolymer. The phosphate-containing group can function as a flame retardant. Since the phosphate-containing group is covalently bonded to the (meth)acrylate copolymer, it does not leach over time like typical groups of many known phosphorus-containing flame retardants.

[0030] The (meth)acrylate copolymer having a pendant group containing phosphate is formed from a first (meth)acrylate copolymer having a pendant carboxylic acid-containing group (i.e., a precursor (meth)acrylate copolymer). The first (meth)acrylate copolymer reacts with an epoxy-functionalized phosphate compound. More specifically, the pendant carboxylic acid-containing group of the first (meth)acrylate copolymer can open the epoxy group of the epoxy-functionalized phosphate compound, resulting in the formation of a second (meth)acrylate copolymer having a pendant group containing phosphate. The phosphate-containing group is covalently bonded to the second (meth)acrylate copolymer. The reaction between the carboxylic acid group of the precursor (meth)acrylate copolymer and the epoxy-functionalized phosphate compound tends to have minimal by-product formation and be very effective.

[0031] This method of forming a (meth)acrylate copolymer having a pendant group containing phosphate offers more advantages than other known methods of introducing a pendant phosphorus-containing group into a polymer material. For example, the preparation of phosphorus-containing monomers can be difficult, and polymerizing other monomers in the presence of a phosphorus-containing monomer can result in a polymer material having a lower molecular weight than desired. That is, the phosphorus-containing monomer can potentially interfere with the radical polymerization process.

[0032] An epoxy-functionalized phosphate compound, a precursor (meth)acrylate copolymer having a pendant carboxylic acid-containing group, a method of forming a (meth)acrylate copolymer having a pendant group containing phosphate, and a (meth)acrylate copolymer having a pendant group containing phosphate are further described below, respectively.

[0033] Epoxy-functionalized phosphate compound An epoxy-functionalized phosphate compound typically has a single epoxy group (oxirane group) and at least one phosphate group. Any known epoxy-functionalized phosphate compound can be used. The number of phosphate groups in the epoxy-functionalized phosphate compound is often equal to 1, 2, or 3, but the number of phosphate groups may be more if desired. A single epoxy group is typically preferred to avoid cross-linking reactions of the precursor (meth)acrylate copolymer when reacting with the epoxy-functionalized phosphate compound.

[0034] Suitable epoxy-functionalized phosphate compounds are often of formula (I)

Chemical formula

[0035] Some specific epoxy-functionalized phosphate compounds of formula (I) are of formula (I-A)

Chemical formula

[0036] Examples of the epoxy-functionalized compounds of formula (I-A) include phosphoric acid, dimethyloxiranylmethyl ester where both R 3 and R 4 are methyl; phosphoric acid, diethyloxiranylmethyl ester where both R 3 and R 4 are ethyl; phosphoric acid, dipropyloxiranylmethyl ester where both R 3 and R 4 are propyl; phosphoric acid, ethylmethyldimethyloxiranylmethyl ester when R 3 is methyl and R 4 is ethyl; phosphoric acid, bis(1-methylethyl)oxiranylmethyl ester where both R 3 and R 4 are isopropyl; 1,3,2-dioxaphospholane, 2-(2-oxiranylmethoxy)-, 2-oxide where R 3 and R 4 together form a 5-membered ring; R 3 and R 41,3,2 - dioxaphospholane, 4,5 - dimethyl - 2 - (2 - oxiranylmethoxy)-, 2 - oxide, in which the groups together form a 5 - membered ring substituted with two methyl groups on adjacent carbon atoms; R 3 and R 4 1,3,2 - dioxaphosphorinane, 2 - (2 - oxiranylmethoxy)-, 2 - oxide, in which the groups together form a 6 - membered ring; R 3 and R 4 1,3,2 - dioxaphosphorinane, 5,5 - dimethyl - 2 - (2 - oxiranylmethoxy)-, 2 - oxide, in which the groups together form a 6 - membered ring substituted with two alkyl groups on the same carbon atom; and R 3 and R 4 Phosphoric acid, oxiranylmethylbis(phenylmethyl) ester, in which both R and R are benzyl, are exemplified, but not limited thereto.

[0037] Other epoxy - functionalized compounds of formula (I) are those of formula (I - B)

Chemical formula

[0038] Examples of the epoxy - functionalized compounds of formula (I - B) include R 1is hydrogen, R 5 is methyl, R 6 is methyl, R 7 is ethyl, R 8 is ethyl, xylitol, 1,2 - anhydro - 3,5 - dideoxy - 3 - methyl -, diethyl phosphate; R 1 is methyl, R 5 is hydrogen, R 6 is propyl, R 7 is ethyl, R 8 is ethyl, phosphoric acid, diethyl 1 - [(3 - methyloxiranyl)methyl]propyl ester; R 1 is hydrogen, R 5 is hydrogen, R 6 is methyl, R 7 is ethyl, R 8 is ethyl, pentitol, 1,2 - anhydro - 3,5 - dideoxy -, 4 - (diethyl phosphate), and the like, but not limited thereto.

[0039] Still other epoxy - functionalized compounds of formula (I) are of formula (I - C)

Chemical formula

[0040] Examples of the epoxy - functionalized compounds of formula (I - C) include CAS number 2620837 - 91 - 2 where R 9 , R 10 , and R 11 are each methyl; and R 9is hydrogen, and R 10 is methyl, and R 11 is methyl, and examples include CAS No. 2620837-90-2, but are not limited thereto.

[0041] Still other epoxy-functionalized compounds are those of formula (II)

Chemical formula

[0042] Examples of formula (II) are 2-(oxiranemethanammonium), N,N,N-tris(2-hydroxyethyldiethylphosphate) as shown below.

Chemical formula

[0043] In many embodiments, the epoxy-functionalized phosphate compound is of formula (I). In some applications where high adhesion strength is required, salts such as those of formula (II) can have an adverse effect on the adhesion properties of the second (meth)acrylate copolymer when used as a pressure-sensitive adhesive. However, in some embodiments, the epoxy-functionalized phosphate compound is of formula (II) and is advantageously used from a higher phosphate content that can promote improvement in flame retardancy.

[0044] Precursor (meth)acrylate copolymer having pendant carboxylic acid-containing groups The precursor (meth)acrylate copolymer has pendant carboxylic acid-containing groups that can react with the epoxy-functionalized phosphate compound. Any suitable monomer having a carboxylic acid-containing group can be included in the monomer mixture used to form the precursor (meth)acrylate copolymer.

[0045] Examples of monomers having a carboxylic acid-containing 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 having a carboxylic acid-containing group is acrylic acid, methacrylic acid, or a mixture thereof.

[0046] The monomer having a carboxylic acid-containing group may be present in an amount in the range of 0.1 to 25% by weight, based on the total weight of the monomers in the monomer mixture used to form the precursor (meth)acrylate copolymer. Similarly stated, the precursor (meth)acrylate copolymer contains from 0.1 to 25 weight percent of monomer units having pendant carboxylic acid-containing groups, based on the total weight of the precursor (meth)acrylate copolymer. This amount may be at least 0.1%, at least 0.2%, at least 0.3%, at least 0.5%, at least 1%, at least 2%, at least 3%, at least 5%, at least 10%, at least 15%, or at least 20 weight percent, and up to 25%, up to 20%, up to 15%, up to 10%, or up to 5 weight percent. This range may be, for example, 0.1 to 20%, 1 to 20%, 0.1 to 15%, 1 to 15%, 0.1 to 10%, or 1 to 10% by weight, 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.

[0047] The precursor (meth)acrylate is often selected to be a pressure-sensitive adhesive, such that the resulting (meth)acrylate copolymer having pendant groups containing phosphate is also a pressure-sensitive adhesive. That is, the monomers are selected to form a precursor (meth)acrylate copolymer that is an elastomeric material. The elastomeric material typically has a glass transition temperature (Tg) of 20 °C or lower, 10 °C or lower, 0 °C or lower, -10 °C or lower, -20 °C or lower, -30 °C or lower, -40 °C or lower, or -50 °C or lower. The glass transition temperature can be measured using techniques such as differential scanning calorimetry and dynamic mechanical analysis. Alternatively, the glass transition temperature can be estimated using the Fox equation. Lists of glass transition temperatures of homopolymers are available from multiple 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., J. Chem. Inf. Comput. Sci., 2002, 42, 232-240.

[0048] To form an elastomeric precursor (meth)acrylate copolymer, the monomer composition often contains at least one low-Tg monomer. As used herein, the term "low-Tg monomer" refers to a monomer that has a Tg of 20 °C or lower when polymerized alone (i.e., a homopolymer formed from the low-Tg monomer has a Tg of 20 °C or lower). Suitable low-Tg monomers are often selected from alkyl (meth)acrylates, heteroalkyl (meth)acrylates, aryl-substituted alkyl acrylates, and aryloxy-substituted alkyl acrylates.

[0049] Examples of low Tg alkyl (meth)acrylate monomers are often non-tertiary alkyl acrylates, but may also be alkyl methacrylates having a linear alkyl group with at least 4 carbon atoms. Specific examples of alkyl (meth)acrylates 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, isotridecyl acrylate, n-octadecyl acrylate, isostearyl acrylate, and n-dodecyl methacrylate.

[0050] Examples of low Tg heteroalkyl (meth)acrylate monomers often 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 heteroalkyl (meth)acrylates include, but are not limited to, 2-ethoxyethyl acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, 2-methoxyethyl (meth)acrylate, and tetrahydrofurfuryl (meth)acrylate.

[0051] Exemplary aryl-substituted alkyl acrylates or aryloxy-substituted alkyl acrylates include, but are not limited to, 2-biphenylhexyl acrylate, benzyl acrylate, 2-phenoxyethyl acrylate, and 2-phenylethyl acrylate.

[0052] The monomer mixture used to form the precursor (meth)acrylate copolymer often contains at least 40 weight percent of a low Tg monomer, based on the total weight of the monomers in the monomer mixture used to form the precursor (meth)acrylate. In some embodiments, the second monomer composition contains at least 45 weight percent, at least 50 weight percent, at least 60 weight percent, at least 65 weight percent, at least 70 weight percent, at least 75 weight percent, or at least 80 weight percent, and up to 99.9 weight percent, up to 99 weight percent, up to 98 weight percent, up to 95 weight percent, up to 90 weight percent, up to 85 weight percent, up to 80 weight percent, or up to 75 weight percent of the low Tg monomer.

[0053] The monomer mixture used to form the precursor can optionally contain a high Tg monomer. As used herein, the term "high Tg monomer" refers to a monomer that, when polymerized alone, has a Tg above 30 °C, above 40 °C, or above 50 °C (i.e., the homopolymer formed from the monomer has a Tg above 30 °C, above 40 °C, or above 50 °C). Some suitable high Tg monomers, such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl (meth)acrylate, cyclohexyl methacrylate, isobornyl (meth)acrylate, stearyl (meth)acrylate, phenyl acrylate, benzyl methacrylate, 3,3,5 trimethylcyclohexyl (meth)acrylate, 2-phenoxyethyl methacrylate, N-octyl (meth)acrylamide, and mixtures thereof, have a single (meth)acryloyl group. Other suitable high Tg monomers, such as various vinyl ethers (e.g., vinyl methyl ether), vinyl esters (e.g., vinyl acetate and vinyl propionate), styrene, substituted styrenes (e.g., a-methylstyrene), vinyl halides, and mixtures thereof, have a single vinyl group that is not a (meth)acryloyl group. Vinyl monomers having groups characteristic of polar monomers are considered polar monomers herein.

[0054] The amount of the high-Tg monomer may be up to 50 wt% or even more, provided that the Tg of the (meth)acrylate copolymer is 20 °C or lower. In some embodiments, this amount may be up to 40 wt%, up to 30 wt%, up to 20 wt%, up to 15 wt%, or up to 10 wt%. This amount may be at least 0.1 wt%, at least 0.5 wt%, at least 1 wt%, at least 2 wt%, or at least 5 wt%. For example, this amount may range from 0 to 50 wt%, from 0 to 40 wt%, from 0 to 30 wt%, from 0 to 20 wt%, from 0 to 10 wt%, from 1 to 30 wt%, from 1 to 20 wt%, or from 1 to 10 wt%. The value of this amount is based on the total weight of the monomers in the monomer mixture used to form the precursor (meth)acrylate copolymer.

[0055] In addition to the monomer having a carboxylic acid-containing group, the monomer mixture can include other polar monomers. The non-acidic polar group can be a hydroxyl group, a primary amide group, a secondary amide group, a tertiary amide group, an amino group, or an ether group. By having a polar group, the adhesion of the pressure-sensitive adhesive to various substrates can be promoted. The polar group is typically not an epoxy group that can react with the pendant carboxylic acid-containing group to result in crosslinking of the precursor (meth)acrylate copolymer.

[0056] Exemplary polar monomers having a hydroxyl group include 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)acrylamide or 3-hydroxypropyl (meth)acrylamide), ethoxylated hydroxyethyl (meth)acrylate (e.g., monomers commercially available under the trade names CD570, CD571, and CD572 from Sartomer (Exton, PA, USA)), and aryloxy-substituted hydroxyalkyl (meth)acrylate (e.g., 2-hydroxy-2-phenoxypropyl (meth)acrylate), but are not limited thereto.

[0057] Exemplary polar monomers having a primary amide group include (meth)acrylamide. Exemplary polar monomers having a secondary amide group include 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, but are not limited thereto.

[0058] Exemplary polar monomers having a tertiary amide group include 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, but are not limited thereto.

[0059] Examples of polar monomers having an amino group include various N,N-dialkylaminoalkyl (meth)acrylates 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)acrylate, and N,N-diethylaminopropyl (meth)acrylamide.

[0060] Examples of polar monomers having an ether bond include those containing poly(alkylene oxide) segments such as poly(ethylene oxide) (meth)acrylate, poly(propylene oxide) (meth)acrylate, poly(tetramethylene oxide) (meth)acrylate, and di(ethylene glycol) ethyl ether (meth)acrylate. Monomers of any suitable molecular weight can be used.

[0061] The amount of the optionally included non-acidic polar monomer is often in the range of 0 to 15% by weight, based on the weight of the monomers in the monomer mixture used to form the precursor (meth)acrylate copolymer. When present, the amount of the non-acidic polar monomer in the monomer mixture is often at least 0.1 weight percent, 0.2 weight percent, 0.5 weight percent, or 1 weight percent, based on the total weight of the monomers in the monomer mixture. This amount can be up to 15% by weight, up to 10% by weight, or up to 5% by weight. For example, this amount is often in the range of 0 to 15% by weight, 0.1 to 10% by weight, 0.5 to 5% by weight, or 1 to 5% by weight, based on the total weight of the monomers in the monomer mixture.

[0062] As a whole, the precursor (meth)acrylate copolymer can be formed from a monomer mixture containing 0.1 to 25 weight percent of a monomer having a carboxylic acid-containing group, 40 to 99.9 weight percent of a low Tg monomer, 0 to 50 weight percent of a high Tg monomer, and 0 to 15 weight percent of a non-acidic polar monomer. In other embodiments, the monomer mixture contains 1 to 20 weight percent of a monomer having a carboxylic acid-containing group, 50 to 99 weight percent of a low Tg monomer, 0 to 40 weight percent of a high Tg monomer, and 0 to 10 weight percent of a non-acidic polar monomer. In yet other embodiments, the monomer mixture contains 5 to 20 weight percent of a monomer having a carboxylic acid-containing group, 50 to 95 weight percent of a low Tg monomer, 0 to 30 weight percent of a high Tg monomer, and 0 to 10 weight percent of a non-acidic polar monomer. In yet other embodiments, the monomer mixture contains 5 to 15 weight percent of a monomer having a carboxylic acid-containing group, 60 to 95 weight percent of a low Tg monomer, 0 to 20 weight percent of a high Tg monomer, and 0 to 10 weight percent of a non-acidic polar monomer. The total of all monomers is 100 weight percent.

[0063] (Meth)acrylate copolymer typically has a weight average molecular weight in the range of 10,000 Da to 1,000,000 Da, or even higher if the (meth)acrylate copolymer is cross-linked. For example, the weight average molecular weight can be at least 20,000 Da, at least 30,000 Da, at least 40,000 Da, or at least 50,000, and can be up to 1,000,000 Da, up to 900,000 Da, up to 800,000 Da, up to 700,000 Da, or up to 600,000 Da.

[0064] Typically, an initiator is added to the monomer mixture to prepare the precursor (meth)acrylate copolymer. The amount of the initiator is typically in the range of 0.01 to 1 weight percent based on the total weight of the monomers in the monomer mixture.

[0065] Exemplary thermal initiators include various azo compounds such as those commercially available under the trade name VAZO from Chemours Co. (Wilmington, DE, USA), for example, VAZO 67 which is 2,2’-azobis(2-methylbutanenitrile), VAZO 64 which is 2,2’-azobis(isobutyronitrile), VAZO 52 which is (2,2’-azobis(2,4-dimethylpentanenitrile), and VAZO 88 which is 1,1’-azobis(cyclohexanecarbonitrile); various peroxides such as benzoyl peroxide, cyclohexane peroxide, lauroyl peroxide, di-tert-amyl peroxide, tert-butyl peroxybenzoate, di-cumyl peroxide, and peroxides commercially available under the trade name LUPERSOL from Atofina Chemical, Inc. (Philadelphia, PA, USA) (for example, LUPERSOL 101 which is 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, and LUPERSOL 130 which is 2,5-dimethyl-2,5-di-(tert-butylperoxy)-3-hexyne); various hydroperoxides such as tert-amyl hydroperoxide and tert-butyl hydroperoxide; and mixtures thereof.

[0066] Some exemplary photoinitiators are benzoin ethers (such as benzoin methyl ether or benzoin isopropyl ether), or substituted benzoin ethers (such as anisoin methyl ether). Other exemplary photoinitiators are substituted acetophenones such as 2,2 - diethoxyacetophenone or 2,2 - dimethoxy - 2 - phenylacetophenone (commercially available under the trade name OMNIRAD 651 from iGM Resins (Charlotte, NC, USA), or under the trade name ESACURE KB - 1 from Sartomer (Exton, PA, USA)). Still other exemplary photoinitiators are substituted α - ketols such as 2 - methyl - 2 - hydroxypropiophenone, 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 - hydroxycyclohexyl phenyl 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 - propan - 1 - one (commercially available under the trade name OMNIRAD 2959), 2 - benzyl - 2 - dimethylamino - 1 - (4 - morpholinophenyl) butanone (commercially available under the trade name OMNIRAD 369), 2 - methyl - 1 - [4 - (methylthio)phenyl] - 2 - morpholinopropan - 1 - one (commercially available under the trade name OMNIRAD 907), and 2 - hydroxy - 2 - methyl - 1 - phenylpropan - 1 - one (commercially available under the trade name DAROCUR 1173 from BASF Corp. (Florham Park, NJ, USA)).

[0067] Precursor (meth)acrylates are often prepared in an organic solvent so that they can readily react with an epoxy-functionalized phosphate compound 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 ether, etc. These solvents may be used alone or as a mixture. The reaction mixture can contain any suitable amount of organic solvent, such as up to 80 weight percent, up to 70 weight percent, up to 60 weight percent, up to 50 weight percent, up to 40 weight percent, or up to 30 weight percent based on the total weight of the reaction mixture.

[0068] (Meth)acrylate copolymer having a pendant group containing phosphate A precursor (meth)acrylate copolymer having a pendant carboxylic acid-containing group (i.e., the first (meth)acrylate copolymer) reacts with an epoxy-functionalized phosphate compound to form a second (meth)acrylate copolymer having a pendant group containing phosphate. This reaction is often 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 an organic solvent or in the presence of a small amount of an organic solvent, an organic solvent can be added to the reaction mixture used to form the second (meth)acrylate copolymer having a pendant group containing phosphate. Suitable organic solvents and amounts are the same as those listed above for use in the preparation of the precursor (meth)acrylate copolymer.

[0069] When the precursor (meth)acrylate copolymer has (meth)acrylic acid monomer units, the monomer groups formed by the reaction of the epoxy-functionalized phosphate compound of formula (I) are of formula (III) as shown in reaction scheme A.

[0070] Reaction Scheme A [Chemical formula] In formula (III), the group R 20 is hydrogen or methyl. The group R 1 is hydrogen or C1-C3 alkyl. The group R 2 is C1-C8 alkylene or a C3-C8 ether group. The group R 3 is C1-C4 alkyl, benzyl, or R 4 together with R forms a cyclic group having 5 or 6 ring members which may be optionally substituted with C1-C3 alkyl. The group R 4 is C1-C4 alkyl, benzyl, or R 3 together with R forms a cyclic group having 5 or 6 ring members which may be optionally substituted with C1-C3 alkyl.

[0071] When the epoxy-functionalized phosphate compound is of formula (I-A), the reaction product after reaction with the (meth)acrylic monomer unit is of formula (III-A) [Chemical formula] of the monomer unit. In formula (III-A), the groups R 20 , R 3 , and R 4 are the same as those described above.

[0072] The pendant group in formula (III-A) is -(C=O)-O-CH2-CH(OH)-CH2-O-(P=O)(OR 3 )(OR 4 ). Similarly, the pendant group of the reaction product of the (meth)acrylic monomer unit and the epoxy-functionalized phosphate compound of formula (I-B) is -(C=O)-O-CHR 1 -CH(OH)-CHR 5 -CHR 6 -O-(P=O)(OR 7 )(OR 8and the reaction product with the epoxy-functionalized phosphate compound of formula (I-C) is -(C=O)-O-CH2-CH(OH)-CH2-O-CHR 9 -CH2-O-(P=O)(OR 10 )(OR 11 ). The groups R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 , R 10 and R 11 are the same as above.

[0073] Similarly, when the precursor (meth)acrylate copolymer has (meth)acrylic acid monomer units, the monomer groups formed by the reaction of the epoxy-functionalized phosphate compound of formula (II) are of formula (IV)

Chemical formula

[0074] Typically, about 25 to 100 mole percent of the monomer units having carboxylic acid-containing groups in the precursor (meth)acrylate copolymer react with the epoxy-functionalized phosphate compound to produce a (meth)acrylate copolymer having pendant groups containing phosphate (i.e., the second (meth)acrylate copolymer). The conversion of monomer units having pendant carboxylic acid-containing groups to monomer units having pendant groups containing phosphate is at least 25 mole percent, at least 30 mole percent, at least 35 mole percent, at least 40 mole percent, at least 50 mole percent, at least 60 mole percent, at least 70 mole percent, or at least 75 mole percent, and can be up to 100 mole percent, up to 95 mole percent, up to 90 mole percent, up to 85 mole percent, up to 80 mole percent, up to 75 mole percent, up to 70 mole percent, up to 65 mole percent, up to 60 mole percent, up to 55 mole percent, or up to 50 mole percent, based on the total moles of monomer units having pendant carboxylic acid-containing groups in the precursor (meth)acrylate copolymer. It can be advantageous to retain at least a portion of the monomer units having pendant carboxylic acid-containing groups to enhance the adhesion of the pressure-sensitive adhesive composition to various substrates. On the other hand, as the amount of phosphate-containing groups increases, the flame retardancy of the pressure-sensitive adhesive tends to be enhanced. These two properties are thought to determine the best balance of pendant groups for a particular application.

[0075] In some embodiments, the second (meth)acrylate copolymer having a pendant group containing phosphate contains 0.1 to 10% by weight of phosphorus-containing monomer units based on the total weight of the second (meth)acrylate copolymer. This amount can be at least 0.1% by weight, at least 0.2% by weight, at least 0.3% by weight, at least 0.5% by weight, at least 1% by weight, at least 2% by weight, at least 3% by weight, at least 4% by weight, or at least 5% by weight, and up to 10% by weight, up to 9% by weight, up to 8% by weight, up to 7% by weight, up to 6% by weight, up to 5% by weight, up to 4% by weight, up to 3% by weight, or up to 2% by weight.

[0076] In some embodiments, the second (meth)acrylate copolymer having a pendant group containing phosphate is halogen-free. In these embodiments, the epoxy-functionalized phosphate compound is not a chloride salt.

[0077] The second (meth)acrylate compound does not contain other phosphorus-containing groups other than the phosphate-containing group of formula (A). That is, the second (meth)acrylate copolymer does not contain or substantially contains phosphinate groups and phosphonate groups. As used herein with respect to phosphinate and / or phosphonate groups, the second (meth)acrylate copolymer contains less than 0.1 weight percent of monomer units having these phosphorus-containing pendant groups. This amount is often less than 0.05 weight percent or less than 0.01 weight percent based on the total weight of the second (meth)acrylate copolymer.

[0078] Coating composition To form a pressure-sensitive adhesive article containing a second (meth)acrylate copolymer having a pendant group containing phosphate, the coating composition is disposed adjacent to a substrate. The coating composition typically includes a second (meth)acrylate copolymer and an organic solvent such as those described above. These coating compositions can be prepared to be visually transparent.

[0079] In some embodiments, the coating composition further optionally includes a tackifier. Useful tackifiers include, for example, rosin ester resins, terpene phenol resins, and hydrocarbon resins. The amount of the optional tackifier is often in the range of 0 to 30 weight percent based on the solids of the coating composition. When present, the amount of the tackifier can be at least 5 wt%, at least 10 wt%, at least 15 wt%, or at least 20 wt% and up to 40 wt%, up to 35 wt%, up to 30 wt%, up to 25 wt%, or up to 20 wt% based on the total weight of the solids in the coating composition.

[0080] Other components commonly added to pressure-sensitive adhesives can be included in the coating composition. Such components include, for example, antioxidants, fillers, pigments, and the like. Any suitable amount can be used as long as the coating composition is a pressure-sensitive adhesive when dry.

[0081] Pressure-sensitive adhesive article The coating composition is typically applied adjacent to a substrate to provide a pressure-sensitive adhesive article. The term "adjacent" means that the coating composition is in contact with the substrate or is separated by another layer such as an adhesion promoter layer. The pressure-sensitive adhesive article typically includes a layer of a permanent or temporary substrate.

[0082] Any suitable substrate can be used. For example, the substrate can be flexible or non-flexible and can be formed from a polymeric material, a glass or ceramic material, a metal (including various alloys), or combinations thereof. In many embodiments, the substrate is glass, a ceramic material, or a metal. In other embodiments, the substrate is a polymeric material such as, for example, a polymer film or a plastic composite (e.g., glass or fiber-filled plastic). The polymer film can be prepared from, for example, polyolefins (e.g., polyethylene, polypropylene, or copolymers thereof), polyurethanes, polyvinyl acetate, polyvinyl chloride, polyesters (polyethylene terephthalate, or polyethylene naphthalate), polycarbonates, polymethyl (meth)acrylate (PMMA), ethylene / vinyl acetate copolymers, polyamides, cellulosic materials (e.g., cellulose acetate, triacetate cellulose, and ethyl cellulose), etc. These substrates are permanent substrates as they cannot be easily removed from the pressure-sensitive adhesive composition.

[0083] In some embodiments, the substrate is a temporary substrate such as a release liner. The role of the temporary substrate is to support the pressure-sensitive adhesive composition until the pressure-sensitive adhesive composition is applied to the permanent substrate. Such articles are often referred to as transfer tapes. The release liner can be on one or both outer surfaces of the pressure-sensitive adhesive layer. Suitable release liners typically have a low affinity for the pressure-sensitive adhesive curable composition. Exemplary release liners can be prepared from paper (e.g., kraft paper), or other types of polymeric materials. Some release liners are coated with an outer layer of a release agent such as a silicone-containing material or a fluorocarbon-containing material (e.g., polyfluoropolyether or polytetrafluoroethylene).

[0084] When the coating composition contains an organic solvent, the coating is applied to a substrate, which can be either permanent or temporary, and then dried to remove the organic solvent. The drying temperature can be room temperature (e.g., 20 - 25 degrees Celsius) or higher.

[0085] The resulting article can have flame retardancy. For example, the article can have a flammability rating of UL94VTM - 0. The present invention includes the following aspects. (1) A method for forming a (meth)acrylate copolymer having a pendant group containing phosphate, the method comprising: providing a precursor (meth)acrylate copolymer having monomer units containing pendant carboxylic acid groups; forming a reaction mixture comprising the precursor (meth)acrylate copolymer and an epoxy-functionalized phosphate compound; reacting the epoxy-functionalized phosphate compound with the pendant carboxylic acid groups of the precursor (meth)acrylate copolymer to form a (meth)acrylate copolymer having a pendant group containing phosphate. A method comprising the above. (2) The method according to item 1, wherein the (meth)acrylate copolymer having a pendant compound containing phosphate is a component of a pressure-sensitive adhesive. (3) The method according to item 1 or 2, wherein the epoxy-functionalized phosphate compound has a single epoxy group and 1 to 3 phosphate groups. (4) The epoxy-functionalized phosphate compound is of formula (I)

Chemical formula

Chemical formula

Chemical formula

Chem.

Chem.

Example

[0086] Unless otherwise specified, all parts, percentages, ratios, etc. in the examples and other parts of this specification are based on weight. Preparation examples are identified by the label prefix "PE", comparative examples are identified by the label prefix "CE", and examples are identified by the label prefix "EX".

[0087] Unless otherwise instructed, all other reagents were obtained from fine chemical suppliers such as MilliporeSigma, Burlington, MA, USA, or were available, or could be synthesized by known methods. Table 1 (below) lists the materials used in the examples and their suppliers.

Table 1

[0088] Test Method UL94 VTM Flammability Test Adhesive samples were laminated between 0.05 mm thick Kapton polyimide films. The laminated samples (adhesive placed between two polyimide films) were approximately 0.25 mm thick. The UL94 VTM test developed by UL, LLC (Northbrook, IL, USA) was used to grade the flammability of these laminate samples, provided that the samples received no pretreatment. After each sample was wrapped around a mandrel, it was fixed to a stand. In this test, a flame from a Bunsen burner was applied twice for 3 seconds (s). The second flame application started immediately after the first combustion time ended. The height of the flame was 20 mm. The possible flammability grades in the UL94 VTM test are listed in Table 2 below.

Table 2

[0089] 90° Angle Peel Adhesion Strength Test The peel adhesion strength was measured at a peel rate of 305 mm / min (12 inches / min) at a 90° angle using an IMASS SP-200 Slip / Peel Tester (available from IMASS, Inc., Accord MA, USA). The substrate panel was wiped with a tissue moistened with isopropyl alcohol (IPA), and the panel was wiped 8 - 10 times while pressing firmly by hand to prepare the test panel. This procedure was repeated two more times using a clean tissue moistened with the solvent. The washed panel was dried. The adhesive tape was cut into strips approximately 1.27 cm × 20 cm (1 / 2 inch × 8 inches), and this strip was applied to the washed panel by rolling it twice with a 2.0 kg (4.5 lb.) rubber roller. The prepared specimens were stored at 23°C and 50% relative humidity for 24 hours and then tested. Two samples were tested for each example, and the average value was expressed in N / cm. Attention was paid to the failure mode and recorded as COH - cohesive mode (i.e., the adhesive split leaving residues on both the tape and the test surface), ADH - adhesive mode (i.e., the adhesive peeled cleanly from the test surface), and / or 2 - B (2 - bond) - the adhesive peeled from the backing material.

[0090] Preparation Example PE1: FRRA1

Chemical Formula

[0091] Epoxy-functionalized monophosphate (flame retardant reactive additive 1 or FRRA1) was synthesized by reacting diethylchlorophosphate with glycidol. 20.63 g of diethylchlorophosphate (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 make a homogeneous solution. Next, 14.82 g of glycidol (0.2 mol) was added dropwise to the solution over 30 minutes. After the addition was complete, the mixture was brought to room temperature and kept at room temperature with stirring for 1 day to complete the reaction. After 1 day, the insoluble white solid was removed by simple filtration using a sintered frit disk funnel (pore size 10 - 20 μm). The reaction solvent and unreacted reagents were removed under reduced pressure using a rotary evaporator. A slightly yellow transparent liquid was obtained.

[0092] Preparation Example PE2: FRRA2 The synthesis of the epoxy-functionalized triphosphate additive (flame retardant additive 2 or FRRA2) was carried out in two main steps. First, tertiary amine-functionalized triphosphate (TATP) was synthesized and isolated as a synthetic intermediate. Second, TATP was reacted with epichlorohydrin to obtain FRRA2 as the final product. [Chemical formula]

[0093] The tertiary amine-functionalized triphosphate (TATP) was synthesized as follows. The first step was to react diethylchlorophosphate with triethanolamine. 56.94 g of diethylchlorophosphate (0.33 mol), 60.71 g of triethylamine (0.6 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 form a homogeneous solution. Then, 14.92 g of triethanolamine (0.1 mol) was added dropwise to the solution over 30 minutes. After the addition was complete, the mixture was brought to room temperature and kept at room temperature with stirring for 1 day to complete the reaction. After 1 day, the insoluble white solid was removed by simple filtration using a sintered frit disk funnel (pore size 10 - 20 μm). The reaction solvent and unreacted reagents were removed under reduced pressure using a rotary evaporator. TATP was obtained as a slightly yellow transparent liquid. [Chemical formula]

[0094] The epoxy-functionalized triphosphate additive (flame retardant reactive additive 2 or FRRA2) was synthesized as follows. 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 rolling mill and mixed at room temperature for 24 hours. The final product (FRRA2) was 1 analyzed by 13 H and

[0095] Preparation Example PE3: Precursor copolymer The precursor (meth)acrylate copolymer was prepared by radical polymerization of two monomers: 2-EHA (186.0 g) and AA (14.0 g). The monomers were mixed at room temperature in a polymerization solvent (ethyl acetate, 300.0 g) and a thermal radical initiator (VAZO67, 0.2 wt%, 0.4 g relative to the total monomers) in an amber narrow-mouth pint bottle to reach a monomer concentration of 40.0 wt%. The solution was degassed by nitrogen purge at room temperature for 5 minutes. The bottle was tightly capped and placed in a LAUNDER-O-METER (SDL Atlas USA, RockHill, SC, USA) at 60 °C for 24 hours. The bottle was cooled to room temperature, and the resulting copolymer solution was used in the formulation of the examples.

[0096] Examples EX1 to EX4 and Comparative Examples CE1 to CE3 The compositions in Table 3 were combined in 40 mL vials and placed on a mixing roller. The solution was mixed on the roller at room temperature for at least 24 hours. The formulations containing 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 transparent and homogeneous.

Table 3

[0097] The coatings were prepared by using a square applicator (wet gap thickness: 0.2 mm) on PET (for adhesion test) and KAPTON HN (for flammability test) substrates. The coatings were dried in a convection oven at 70 °C for at least 30 minutes. The dried coatings were stored under controlled temperature and humidity (23 °C, relative humidity 50%) for at least 24 hours and then evaluated.

[0098] Dried coatings of the materials in Table 3 (on KAPTON HN film) were prepared and tested according to the procedure of the UL94 VTM flammability test. The results are shown in Table 4.

Table 4

[0099] Adhesives without flame retardants and adhesives containing non-reactive flame retardants all burned up to the top upon the first application of the flame. Coatings containing reactive monophosphates and triphosphates burned out rapidly before the flame reached the end of the sample. Even upon the second application, the flame went out 10 seconds earlier, achieving the VTM0 rating.

[0100] Dry coatings of the materials in Table 3 (on PET films) were prepared and tested according to the procedure of the 90° peel adhesion strength test. The results are shown in Table 5.

Table 5

Claims

1. A method for forming a (meth)acrylate copolymer having a pendant group containing a phosphate, the method comprising: providing a precursor (meth)acrylate copolymer having monomer units containing pendant carboxylic acid groups; forming a reaction mixture comprising the precursor (meth)acrylate copolymer and an epoxy-functionalized phosphate compound; reacting the epoxy-functionalized phosphate compound with the pendant carboxylic acid groups of the precursor (meth)acrylate copolymer to form a (meth)acrylate copolymer having a pendant group containing a phosphate; wherein the epoxy-functionalized phosphate compound has a single epoxy group and 1 to 3 phosphate groups.

2. The method according to claim 1, wherein the (meth)acrylate copolymer having a pendant compound containing a phosphate is a component of a pressure-sensitive adhesive.

3. The method according to claim 1, wherein the epoxy-functionalized phosphate compound has the formula (I) 【Chemical 1】 (wherein, R １ is hydrogen or methyl, R ２ is a C1-C8 alkylene or C3-C8 ether group, R ３ is C1-C4 alkyl, benzyl, or R ４ together with forms a cyclic group having 5 or 6 ring members optionally substituted with C1-C3 alkyl, R ４ is C1-C4 alkyl, benzyl, or R ３ together with forms a cyclic group having 5 or 6 ring members, optionally substituted with C1-C3 alkyl) ).

4. The method according to claim 3, wherein the epoxy-functionalized phosphate compound of formula (I) has the formula (I-A) 【Chemical Formula 2】 ).

5. The method according to claim 3, wherein the epoxy-functionalized phosphate compound of formula (I) has the formula (I-B) 【Chemical Formula 3】 (wherein, R １ is hydrogen or C1-C3 alkyl, R ５ is hydrogen or C1-C3 alkyl, R ６ (wherein R is C1-C3 alkyl) ).

6. The method according to claim 3, wherein the epoxy-functionalized phosphate compound of formula (I) has the formula (I-C) [Chemical Formula 4] (wherein, R ９ is hydrogen or C1-C3 alkyl, R １０ is C1-C3 alkyl, R １１ is C1-C3 alkyl) ).

7. The method according to claim 1, wherein the epoxy-functionalized phosphate compound has the formula (II) 【Chemical Formula 5】 (wherein, R １２ is an alkylene having 1 to 2 carbon atoms, R １３ is an alkylene having 2 to 4 carbon atoms, R １４ is C1-C4 alkyl or, together with R １５ forms a cyclic group having 5 or 6 ring members, optionally substituted with C1-C3 alkyl R １５ is C1-C4 alkyl or, together with R １４ forms a cyclic group having 5 or 6 ring members, optionally substituted with C1-C3 alkyl) ).

8. The method according to any one of claims 1 to 7, wherein the precursor (meth)acrylate contains 1 to 20 weight percent of monomer units containing the carboxylic acid groups, based on the total weight of the precursor (meth)acrylate.

9. The method according to claim 8, wherein at least 50 percent of the monomer units containing the carboxylic acid groups in the precursor (meth)acrylate react with the epoxy-functionalized phosphate compound.

10. A pressure-sensitive adhesive comprising a (meth)acrylate copolymer having a pendant group containing a phosphate, wherein the (meth)acrylate copolymer having a pendant group containing a phosphate is a) A precursor (meth)acrylate copolymer having monomer units containing pendant carboxylic acid groups, and b) An epoxy-functionalized phosphate compound having a single epoxy group and 1 to 3 phosphate groups, which is a reaction product of a reaction mixture containing the epoxy-functionalized phosphate compound, and the epoxy group of the epoxy-functionalized phosphate compound has undergone a ring-opening reaction with (meth)acrylic acid monomer units, a pressure-sensitive adhesive.

11. A permanent or temporary substrate, and An article comprising the pressure-sensitive adhesive composition according to claim 10 disposed adjacent to the permanent or temporary substrate.

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

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