WO2018164833A1

WO2018164833A1 - Non-migratory, high-melting/softening polymeric phosphorus-containing flame retardant for printed wiring boards

Info

Publication number: WO2018164833A1
Application number: PCT/US2018/018893
Authority: WO
Inventors: Andrew M. Piotrowski; Meng Zhang; Joseph Zilberman; Eran GLUZ; Sergei Levchik; Anantha Desikan
Original assignee: Icl-Ip America Inc.
Priority date: 2017-03-07
Filing date: 2018-02-21
Publication date: 2018-09-13
Also published as: TW201841977A

Abstract

There is provided herein a flame retardant composition comprising: a compound having the general formula (I): which has a weight average molecular weight of from about 1,000 to about 700,000, and (b) a polyphenylene ether and/or an oligomer thereof. There is also provided an article comprising the flame retardant composition, and a method of making the article.

Description

NON-MIGRATORY, HIGH-MELTING/SOFTENING POLYMERIC PHOSPHORUS- CONTAINING FLAME RETARD ANT FOR PRINTED WIRING BOARDS

FIELD OF THE INVENTION

The present disclosure relates to halogen-free flame retardant compositions and prepregs, metal-clad laminates, and printed-wiring boards containing the same.

BACKGROUND OF THE INVENTION

In recent years, electrical equipment has progressed in high capacity for signals, which demands advanced dielectric characteristics, e.g. lower specific permittivity and lower dielectric loss tangent, which is required for high-speed communications in applications of semiconductor substrates and the like.

Currently, the electrical and electronic industry is rapidly developing. The developing direction of electronic devices is light weight, high performance, high reliability, and

environmental protection.

The specific requirements of laminated sheets for printed circuits are expressed by high heat resistance, low thermal expansion coefficient, high resistance to heat and humidity, environmental friendliness, good flame retardancy, low dielectric constant and dielectric loss, and a high elastic modulus. Conventional epoxy resins have been unable to fully meet development needs of printed circuit laminated sheets, and have been replaced at times with compositions containing poly(arylene ether) having high thermal stability, low dielectric constant and dielectric loss, as well as excellent toughness. In addition, presence of poly(arylene ether) has improved flammability performance, but not enough to pass required flammability tests. Good flame retardancy is particularly important in such demanding applications due to high circuit density and the resultant potential for considerable heat generation therefrom.

Traditional poly(arylene ether) resins are thermoplastic materials with a high molecular weight. The high melting viscosity results in poor flow and poor solubility making the processability of traditional poly(arylene ether) very difficult. In the application of laminated sheets for printed circuits, high molecular-weight poly(arylene ether) is replaced with low- molecular weight, modified polyphenylene ether (PPE) with specific end groups. For example in CN101796132A, the modified PPE with a number average molecular-weight below 5,000 and a cyanate ester compound are used in combination. The copper clad laminates made from this resin composition had a lower dielectric constant and dielectric loss, a better heat resistance, and a low water absorption rate. However, the active groups of the low molecular weight PPE resin, in CN101796132A, are not reactive enough, and almost do not participate in the cross-linking reaction of cyanate esters. The cured product is composed of a semi-interpenetrating network (semi-IPN). The PPE resin in the semi-IPN also cannot cross-link itself, and can only intersperse in the cross-linked network in a free state. Adding a reactive flame retardant will only make this problem worse.

Modification of PPE with end groups containing unsaturated double bonds was much more successful. For example, U.S. Pat. No. 5,071,922 to Nelissen, as well as U.S. Pat. Nos. 6,352,752 and 6,627,704 to Yager each describe that such unsaturated PPE may be widely applied in the thermosetting resin field. In CN102807658, the butadiene-containing polyolefin resins with a greater molecular weight were used as a cross-linking agent, and were blended with components of functionalized PPE resins and initiators to obtain a resin composition used in laminated sheets for printed circuits. The composition has very good dielectric properties and heat resistance, and is suitable for use in high-frequency electronic circuit boards.

It is known that the laminated sheets prepared for printed circuit boards are flammable and usually require the addition of halogenated flame retardants. However, halogenated flame retardants are not desirable for many applications. Moreover, small molecular flame retardants often cause the decreased mechanical properties to deteriorate the material. Migration and volatility problems existing at the same time result in reduced performance and a non-ideal flame retardant effect. Therefore, in thermosetting resin compositions, the replacement of the halogenated flame retardants by organic phosphorous -containing flame retardants has continuously emerged, such as is described in EP A 0384939, EP A 0384940, EP A 0408990, DE A 4308184 DE A 4308185, DE A 4308187, WO A 96/07685, and WO A 96/07686.

However, many of such organic phosphorus-containing flame retardants can also suffer from migrational problems and may require the presence of specific reactive groups, such as epoxy, to be chemically bonded to the resin. A flame retardant that is non-migratory and has sufficient melting/softening point to withstand soldering process without a need to participate in the crosslinking process is thus highly desirable. In addition, for laminated sheets in printed circuits, the current international standards require lead-free processes due to an ever- increasing environmental awareness. Therefore, the requirements for the process performance of the substrates are especially strict, such as the glass transition temperature (Tg) and the heat- resistance in a solder pot, which have become important issues that still remain to be overcome.

SUMMARY OF THE INVENTION

The inventors herein have unexpectedly discovered a halogen-free flame retardant composition consisting of modified PPE (polyphenylene ether) and a phosphorus -containing aromatic polyester with a melting/softening point above 200°C, and which is insoluble in the flame retardant composition. The flame retardant composition can also contain a thermosetting resin, e.g., an epoxy resin, preferably in small amounts, e.g., less than 5% by weight. After curing, the flame retardant composition exhibits a low dielectric coefficient and low levels of dielectric loss, high heat resistance and excellent flame retardancy. The flame retardant composition is shown herein to be suitable for prepregs, laminated sheets for printed circuits, and the like. There has been no previous known disclosure of such materials as non-migratory flame retardants for thermosetting resins, and in particular, for thermosetting resins used in PWB applications. Surprisingly Applicants have discovered that the use of the flame retardant composition herein can provide adequate flame retardancy while maintaining high thermal stability, high Tg and excellent electrical properties.

As shown in Figure 1, the phosphorus-containing aromatic polyesters may interpenetrate the network formed by PPE resin and crosslinking agent. The phosphorus-containing aromatic polyester can also combine with inorganic fillers and intersperse in the crosslinked network in a free state (Figure 2). In addition, the active ester groups of the phosphorus-containing aromatic polyester can react with epoxy resin and form a second crosslinked network (Figure 3). The PPE network and polyester-epoxy network entangle together, leading to a super stable, non-migratory structure with excellent thermal and electrical properties.

DETAILED DESCRIPTION OF THE INVENTION

The expression "non-migratory" as used herein is understood to mean that the

compositions including flame retardant phosphorus-containing aromatic polyesters do not exhibit migration in cured thermosetting products. The expression "high-melting/softening" as used herein is understood to mean that the compound of the general formula (I) as used herein has a melting/softening point above 170 °C and preferably above 190 °C.

The expression "insoluble in the flame retardant composition" is understood to mean that the flame retardant phosphorus-containing aromatic polyester is not soluble in solvents commonly used by industry, such as methyl ethyl ketone (MEK), acetone and other commonly used organic solvents at 25 °C. It is understood by those skilled in the art that solubility will be a function of the molecular weight of the flame retardant phosphorus -containing aromatic polyester and the structure of the flame retardant phosphorus-containing aromatic polyester.

In one embodiment herein the flame retardant composition when employed in a thermoset composition can have a Dk value less than about 3.2, and preferably less than about 3.0 and/or a Df value of less than about 0.01 and preferably less than about 0.005.

There is provided herein, in one embodiment a flame retardant composition comprising a compound having the general formula (I):

(Formula I)

having a weight average molecular weight of from 1,000 to 700,000, preferably from 10,000 to about 100,000 and most preferably from 25,000 to about 50,000, and where X is a bivalent aromatic hydrocarbon group containing from 6 to about 12 carbon atoms, and which includes the non-limiting examples of phenylene groups, naphthalene groups, biphenylene groups, etc., which groups may optionally include a substituent bonded to the aromatic ring, such as an alkyl group or alkoxyl group each containing up to 6 carbon atoms,

Y is selected from the group consisting (i),

(iii) where Z is selected from the group consisting of a covalent bond, -SO2-, -C(CH₃)2-, -CH(CH₃)- and -CH2-; a is an integer of from 0 to 2; and b is an integer of from 0 to 2, and

wherein the wavy lines of each structure of Y indicate the bonds to the oxygen atoms which Y bridges in the general formula (I); R is selected from the roup consisting of H, an alkyl group of from 1 to about 4 carbon atoms,

where R² is selected from the group consisting of H or -C(=0)R³ and where R³ is selected from an alkyl group of from 1 to 4 carbon atoms, such as methyl, ethyl and propyl, a phenyl group, a napthyl group and an aromatic phenol group which is selected from one of a phenol group, o- cresol group, m-cresol group, /?-cresol group, a-naphthol group, and a ?-naphthol group, and when R² is H, R¹ cannot be phenyl or naphtyl, and n is >2, preferably from 2 to about 100, and most preferably from 2 to about 50.

In one non-limiting embodiment herein, the flame retardant composition described herein can comprise a mixture of different structures of the general formula (I), e.g., the mixture can comprise wherein at least 50 wt% of the general formula (I) structures, and preferably more than 70 wt% of the general formula (I) structures are such that Y is chosen from moieties (i) and (ii) as noted above, with the remaining different structures of the general formula (I) being such that Y is chosen from the (iii) moiety noted above.

In one non-limitin embodiment herein, in compound (I), R¹ is

and where X is a bivalent aromatic hydrocarbon group of 6 to 12 carbon atoms which is optionally substituted with an alkyl or alkoxy group of up to 6 carbon atoms.

In one embodiment of compound (I), R¹ is an alkyl of from 1 to 4 carbon atoms and where X is a bivalent aromatic hydrocarbon group of from 6 to 12 carbon atoms which is optionally substituted with an alkyl or alkoxy group of up to 6 carbon atoms.

In one embodiment of compound (I), X is a bivalent aromatic hydrocarbon group of from 6 to 12 carbon atoms which is optionally substituted with an alkyl or alkoxy group of up to 6 carbon atoms.

Some non-limiting examples of compounds of the general formula (I) include, phosphorus-containing aromatic polyesters, such as those described herein, such as co-polymers of 1,4-Benzenediol, 2-(6-oxido-6H-dibenz[c,e][l,2]oxaphosphorin-6-yl)- with aromatic dicarboxylic acids are commercially available. CAS reg# 102338- 15-8 - 1,3- Benzenedicarboxylic acid, polymer with 2-(6-oxido-6H-dibenz[c,e] [l,2]oxaphosphorin-6-yl)- l, 4-phenylene diacetate; CAS reg. #102338-14-7 - 1,2-Benzenedicarboxylic acid, polymer with 2- (6-oxido-6H-dibenz[c,e] [l,2]oxaphosphorin-6-yl)- l,4-phenylene diacetate; and, CAS Reg.#101842-64-2 1,4-Benzenedicarboxylic acid, polymer with l, l'-[2-(6-oxido-6H-dibenz[c,e] [ 1 ,2]oxaphosphorin-6-yl)- 1 ,4-phenylene] diacetate.

The flame retardant composition according to the present invention comprises (b) polyphenylene ether (PPE) or an oligomer thereof. The PPE or its oligomer has two or more vinyl groups, allyl groups, or both at both ends of the molecular chain, and is not particularly limited to the structure and can be used.

In the present invention, modified low molecular weight polyphenylene ether resin with vinyl end-groups represented by the following general formula (II) is preferable. This is because the two sides modified with two or more vinyl groups can satisfy the moisture resistance characteristic and the dielectric property due to the improvement of the glass transition temperature, the low thermal expansion coefficient, and the decrease of hydroxyl group.

Formula (II)

In Formula II, Zi is a divalent moiety derived from compounds selected from the group consisting of bisphenol A, bisphenol F, bisphenol S, naphthalene, anthracene, biphenyl, tetramethyl biphenyl, phenol novolac, cresol novolac, bisphenol A novolak, DOPO-HQ (10~(2,5~ Dihydroxyphenyl) -9,10-dihydro-9-oxa- 10-phospha phenanthrene- 10-oxide) and the group consisting of borane compounds, and mi and m₂ are each independently an integer of from 3 to about 20, preferably from about 4 to about 15 and most preferably from about 5 to about 10. The expression "derived from compounds" as used above is understood to mean that the compound has two hydrogen atoms removed therefrom to provide for two valences which can bridge the adjacent moieties in Formula II above.

In the present invention, those compounds of the formula (II) having at least two vinyl groups at both ends of the molecular chain are preferably used. However, it is also possible to use a conventional unsaturated double bond moiety known in the art in addition to the vinyl group.

It is difficult to produce a multilayer sheet with conventional polyphenylene ether because polyphenylene ether has high melting point and therefore has a high melt viscosity of the resin composition. Therefore, in one embodiment herein the high molecular weight polyphenylene ether (b) as described herein can in one embodiment be a modified form of low molecular weight PPE obtained through a redistribution reaction of high molecular weight PPE.

In one non-limiting embodiment herein, a high molecular weight PPE is understood to be a PPE with a number average molecular weight above the ranges described herein for the PPE component (b).

In one embodiment herein, conventional, polyphenylene ether for a copper-clad laminate can be modified and used as low-molecular polyphenylene ether having a phenolic group at both terminals through a redistribution reaction using a polyphenol and a radical initiator as a catalyst.

The structural characteristics of bisphenol A, and the high polarity of the phenolic groups at both terminals generated after redistribution have previously limited the implementation of low dielectric loss characteristics. In contrast to this, in the present invention, a polyphenylene ether (b) having a low dielectric loss even after crosslinking can be obtained by modifying it into a PPE containing a vinyl group thus producing a PPE having a low polarity. These modified polyphenylene ethers have a lower molecular weight than conventional polyphenylene derived compounds and have a high alkyl content and therefore are excellent in compatibility with conventional epoxy resins and have improved flowability in the production of laminated plates, and the dielectric properties are further improved. Therefore, a printed circuit board

manufactured using the flame retardant composition of the present invention has an advantage of improving physical properties such as moldability, workability, dielectric properties, heat resistance and adhesive strength. Some non-limiting examples of specific bisphenol compounds having an increased alkyl content and aromatic content which can be used herein in a redistribution reaction of high molecular weight PPE, other than bisphenol A [BPA, 2,2-Bis (4-hydroxyphenyl) propane], can be selected from the group consisting of bisphenol AP (1,1 -bis (4-hydroxyphenyl) -1-phenyl- ethane), bisphenol AF (2,2- Bis (4-hydroxyphenyl) butane), bis- (4-hydroxyphenyl)

diphenylmethane, bis (3-methyl-4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) -2,2- dichloroethylene, 2,2-bis (4-hydroxy-3-isopropyl-phenyl) propane, 1,3- Bis (4-hydroxyphenyl) sulfone, 5,5 '- (1-Methylethyliden) -bis [Ι,Γ - (bisphenyl) -2-ol] Propene, 1,1 -bis (4- hydroxyphenyl) -3,3,5-trimethyl-cyclohexane, 1,1 -bis (4-hydroxyphenyl) -cyclohexane, mixtures thereof, and the like.

The polyphenylene ether resin (b) herein may be modified to have a low molecular weight in the range of 1,000 to 10,000, preferably the number average molecular weight (Mn) is in the range of 1000 to 5,000, and more preferably in the range of 1,000 to 3,000.

In the flame retardant composition according to the present invention, the content of the polyphenylene ether resin or oligomer thereof may be about 10 to 80% by weight based on the total weight of the resin, preferably from about 15 to about 60 % by weight and most preferably from about 20 to about 50 % by weight.

The crosslinking agent having a carbon-carbon unsaturated double bond (c) may be selected from the group consisting of a hydrocarbon crosslinking agent (1), a crosslinking agent (2) containing at least three functional groups, and a rubber (3) having a block structure.

In one embodiment, a hydrocarbon crosslinking agent (1), a crosslinking agent (2) containing three or more functional groups, and a rubber (3) having a block structure may be used in combination as the crosslinking curing agent.

The hydrocarbon-based crosslinking agent usable in the present invention is not particularly limited as long as it is a hydrocarbon-based crosslinking agent having a double bond or a triple bond, and may preferably be a diene crosslinking agent. Specific examples thereof include butadiene (e.g., 1,2-butadiene, 1,3-butadiene and the like) or a polymer thereof, decadiene (e.g., 1,9-decadiene) or a polymer thereof, octadiene, etc. or a polymer thereof, vinylcarbazole, etc. These may be used alone or in combination of two or more.

According to one example, polybutadiene represented by the following formula (III) may [ as the hydrocarbon-based crosslinking agent.

Formula (III)

In the above Formula (III), m₃ is an integer of 10 to 30.

The molecular weight (Mw) of the hydrocarbon crosslinking agent may range from 500 to 3,000, preferably from 1,000 to 3,000.

Non-limiting examples of crosslinking agents containing three or more (preferably three to four) functional groups usable in the present invention include triallyl isocyanurate (TAIC), 1,2,4-trivinylcyclo 1,2,4-trivinyl cyclohexane (TVCH), etc. These may be used alone or in combination of two or more.

According to one example, triallyl isocyanurate (TAIC) represented by the following formula (IV) can be used as a crosslinking agent containing three or more functional groups.

Formula (IV)

The rubber of the block structure usable in the present invention may be in the form of a block copolymer, preferably a rubber in the form of a block copolymer containing a butadiene unit, more preferably a butadiene unit and a styrene unit, an acrylonitrile unit, an acrylate unit, and the like. Non-limiting examples include styrene-butadiene rubber (SBR), acrylonitrile- butadiene rubber, acrylate-butadiene rubber, aery lonitrile-butadiene- styrene rubber, etc. Random copolymer poly(styrene-co-butadiene) can also be used. These may be used singly or in combination of two or more kinds.

According to one example, a styrene-butadiene rubber represented by the following formula (V) can be used as a rubber having a block structure.

Formula (V)

wherein m₄ is an integer up to 500, and ms is an integer up to 2100.

A styrene-butadiene copolymer has a number average molecular weight up to 150000 and includes 1,2 vinyl groups having cross-linking properties. Such copolymer including 1,2- vinyl having cross-linked properties is for example a copolymer having structure represented by Formula VI.

Formula (VI)

The number average molecular weight is equal or greater than 2000. The number average molecular weight can be in the range of 2000-150000, and more preferably 3000-120000. In the styrene-butadiene rubber of the invention a styrene content is preferably from 20 to 80 wt % and butadiene content is preferably from 50 to 80% wt. A 1,2- vinyl content in butadiene blocks is preferably from 40 to 85%.

In the thermosetting resin composition of the present invention, the content of the crosslinking agent having a carbon-carbon unsaturated double bond is not particularly limited, but may be in the range of about 5 to 50% by weight based on the total weight of the resin composition, preferably about 10 to 45%. When the content of the cross-linkable curing agent falls within the above-mentioned range, the resin composition has a low dielectric property, curability, moldability and adhesion.

According to one example, when the hydrocarbon crosslinking agent (1) and the crosslinking agent (2) containing three or more functional groups are mixed with PPE crosslinking hardeners, the content of the crosslinking agent (2) containing more than one functional group is in the range of about 1 to 10% by weight, preferably about 2 to 5% by weight.

If necessary, in addition to the above-mentioned hydrocarbon-based curing agent, three or more functional group-containing crosslinking agents and a rubber having a block structure, the present invention may further include a conventional crosslinking curing agent known in the art. At this time, it is preferable that the cross-linkable curing agent has excellent compatibility with polyphenylene ether modified with a vinyl group, an allyl group or the like.

Non-limiting examples of crosslinking agents having a carbon-carbon double bond that can be used include divinylnaphthalene, divinyldiphenyl, styrene monomer, phenol, triallyl cyanurate (TAC), di-(4-vinylbenzyl) Ether, and combination thereof.

Initiators are used in the unsaturated portions of the thermosetting resin to induce any compounds being capable of generating free radicals at high temperature. These initiators include peroxide and non-peroxide initiators. The peroxide initiator is selected from one or more of dicumyl peroxide, t-butyl perbenzoate, 2,5-dimethyl-2,5-di(t-butylperoxy) hex-3-yn, di(t- butyl) peroxide, t-butyl cumyl peroxide, di(t-butylperoxy-m-isopropyl)benzene, 2,5-dimethyl-2,5 di(t-butylperoxy)hexane, di(t-butylperoxy) isophthalic acid, 2,2-di(t-butylperoxy)butane, (benzylphthalidyl peroxy)hexane, di(trimethylsilyl) peroxide. Usually, the non-peroxide initiator is selected from one or more of 2,3-dimethyl-2,3-diphenylbutane, and 2,3-trimethylsilyloxy-2,3- diophenylbutane .

In one embodiment herein the flame retardant composition can be such that if further comprises a thermosetting resin, such as the non-limiting example of an epoxy resin. In one non- limiting embodiment, the epoxy resin can be present in the flame retardant composition in an amount of from about 0.1 % by weight to about 25% by weight, preferably from about 1 to about 15 % by weight, and most preferably from about 1 to about 5 by weight of the flame retardant composition.

The epoxy resin can be such as those selected from halogen-free epoxies, phosphorus- free epoxies, and phosphorus -containing epoxies, and mixtures thereof, including, but not limited to, DEN 438, DER 330 Epon 164 (DEN and DER are trademarks of The Dow Chemical Company), epoxy functional polyoxazolidone-containing compounds, cycloaliphatic epoxies, GMA/styrene copolymers, and the reaction product of DEN 438 and DOPO resins, and combinations of any of the foregoing. The most preferred are low Dk and low Df epoxies for example DCPD (such as EPICLON HP-7200 series) epoxy or epoxidized polybutadiene.

The flame retardant composition can also optionally contain at least one co-crosslinker and/or optionally one or more of a curing catalyst, a Lewis acid, an inhibitor, and a benzoxazine- containing compound. The flame retardant composition optionally may contain at least one additional crosslinkable epoxy resin or a blend of two or more epoxy resins. The flame retardant composition may also optionally contain at least one curing catalyst and at least one inhibitor. All of the above components may be blended or mixed together in any order to form the flame retardant composition.

The flame retardant composition prepared according to the present invention, made by reacting a mixture of compound(s) of the general formula (I) described herein, the PPE resin (b) an optional epoxy resin, and optionally another co-crosslinker (i.e. a curing agent); may be used to make prepregs, laminates and circuit boards useful in the electronics industry and as a phosphorus-containing flame-resistant composition to coat metallic foils for so called build-up technology as described herein.

The flame retardant composition according to the present invention may optionally comprise at least one crosslinking curing agent. The compound(s) (a) of the general formula (I) described herein can be used as a filler material for a thermosetting epoxy resin composition as described herein, and will vary, depending on the specific epoxy resin and the specific compound being employed, as well as the specific parameters of processing as are known by those skilled in the art. The compounds of the general formula (I) can be used as additives in of and by themselves, or in combination with any other organic or inorganic fillers, such as the non-limiting examples of mineral fillers, such as Al(OH)₃, Mg(OH)₂; silica, alumina, titania etc. In addition, compounds (a) of the invention herein can be used in combination with other flame retardants both reactive such as one described in U.S. Patent No. 8,202,948 or additive such as described in U.S. Patent No.

9,012,546, the entire contents of which are incorporated by reference herein in their entireties, and those others described herein. In one embodiment herein the amount of filler other than the compound of the general formula (I) can be from about 1 to about 30 weight percent, from about 3 to about 25 weight percent and most preferably from about 5 to about 20 weight percent.

In one non-limiting embodiment, the effective flame-retardant amount of compound(s) of the general formula (I) described herein which can be used is from about 20 to about 250 parts by weight per 100 parts of the PPE resin component (b), more specifically from about 40 to about 200 parts by weight per 100 parts of the PPE resin component (b), and most specifically from about 60 to about 180 parts by weight per 100 parts of the PPE resin component (b). To provide adequate flame retardancy, the compositions herein will contain from 1% to about 5% phosphorus in the final composition. In one embodiment, the above stated amounts of compound(s) of the general formula (I) described herein can be the amounts of compound(s) of the general formula (I) described herein used in any of the compositions described herein.

As described above, the flame retardant compositions described herein may be formed by blending compound(s) of the general formula (I) described herein, at least one PPE resin (b), optionally at least one epoxy resin, and optionally at least one co-crosslinker, as well as any of the other optional components described herein; or in another embodiment, the phosphorus- containing flame-resistant epoxy resin compositions may be formed by blending at least one compound of the general formula (I), at least one PPE resin (b), at least one epoxy resin, and at least one co-crosslinker, as well as any of the other optional components described herein. With any of the compositions above where an epoxy resin is present, any number of co- crosslinking agents (i.e., in addition to the compound(s) of the general formula (I) described herein) may optionally also be used. Suitable co-crosslinkers that may optionally be present in combination with the epoxy compounds according to the present invention include, for example, multifunctional co-crosslinkers as are known to those skilled in the art.

The co-crosslinkers include, for example, copolymers of styrene and maleic anhydride having a molecular weight (M_w) in the range of from 1,500 to 50,000 and an anhydride content of more than 15 percent. Commercial examples of these materials include SMA 1000, SMA 2000, and SMA 3000 and SMA 4000 having styrene-maleic anhydride ratios of 1: 1, 2: 1, 3: 1 and 4: 1, respectively, and having molecular weights ranging from 6,000 to 15,000, which are available from Elf Atochem S.A.

Other less prefered co-crosslinkers useful in the present invention include hydroxyl- containing compounds. Other phenolic functional materials can also be used but are not as suitable and they include co-crosslinkers which upon heating form a phenolic crosslinking agent having a functionality of at least 2. In one embodiment herein the flame retardant composition can have a low level of phenolic compounds, such as from about 0.001 to about 5%, preferably from about 0.01 to about 2% and most preferably from about 0.01 to about 1% of phenolic compound based on the entire weight of the flame retardant composition.

Any of the flame retardant compositions of the present invention described herein may optionally comprise a curing catalyst. Examples of suitable curing catalyst materials (catalyst) useful in the present invention include compounds containing amine, phosphine, ammonium, phosphonium, arsonium or sulfonium moieties or mixtures thereof. Particularly preferred catalysts are heterocyclic nitrogen-containing compounds.

The amount of optional curing catalyst used depends on the molecular weight of the catalyst, the activity of the catalyst and the speed at which the polymerization is intended to proceed. In general, the curing catalyst is used in an amount of from 0.01 parts per 100 parts of resin (p.h.r.) to about 1.0 p.h.r., more specifically, from about 0.01 p.h.r. to about 0.5 p.h.r. and, most specifically, from about 0.1 p.h.r. to about 0.5 p.h.r. The curable compositions of the present invention may optionally have boric acid and/or maleic acid present as a cure inhibitor. In that case, the curing agent is preferably a polyamine or polyamide. The amount of cure inhibitor will be known by those skilled in the art.

The flame retardant compositions of the present invention may also optionally contain one or more additional flame retardant additives including, for example, red phosphorus, encapsulated red phosphorus or liquid or solid phosphorus -containing compounds, for example, "EXOLIT OP 930", EXOLIT OP 910 from Clariant GmbH and ammonium polyphosphate such as "EXOLIT 700" from Clariant GmbH, a phosphite, or phosphazenes; nitrogen-containing fire retardants and/or synergists, for example melamines, melem, cyanuric acid, isocyanuric acid and derivatives of those nitrogen-containing compounds; halogenated flame retardants and halogenated epoxy resins (especially brominated epoxy resins); synergistic phosphorus-halogen- containing chemicals or compounds containing salts of organic acids; inorganic metal hydrates such as Sb₂03, Sb₃05, aluminum trihydroxide and magnesium hydroxide, such as "ZEROGEN 30" from Martinswerke GmbH of Germany, and more preferably, an aluminum trihydroxide such as "MARTINAL TS-610" from Martinswerke GmbH of Germany; boron-containing compounds; antimony-containing compounds; silica and combinations thereof.

When additional flame retardants which contain phosphorus are present in the

composition of the present invention, the phosphorus-containing flame retardants are preferably present in amounts such that the total phosphorus content of the total resin composition is from 0.2 wt. percent to 5 wt. percent.

The flame retardant compositions of the present invention may also optionally contain other additives of a generally conventional type including for example, stabilizers, other organic or inorganic additives, pigments, wetting agents, flow modifiers, UV light blockers, and fluorescent additives. These additives can be present in amounts of from 0 to 5 wt. percent and are preferably present in amounts of less than 3 wt. percent.

The flame retardant composition is preferably free of bromine atoms, and more preferably free of halogen atoms. The present invention is particularly useful for making B-staged prepregs, laminates, bonding sheets, and resin-coated copper foils by well known techniques in the industry.

In one embodiment herein there is provided an article that contains any of the flame retarded composition(s) described herein. In one embodiment the article herein can be used in lead-free soldering applications and electronic devices, e.g., printed circuit board applications. Specifically, the article can be a prepreg and/or a laminate. In one specific embodiment there is provided a laminate and/or a prepreg that contains any one or more of the flame retardant compositions described herein. In one other embodiment there is provided herein a printed circuit board, optionally a multilayer printed circuit board, comprising one or more prepreg(s) and/or a laminate (either uncured, partially cured or completely cured) wherein said prepreg(s) and/or laminate comprises any one or more of the flame retardant compositions described herein. In one embodiment there is provided a printed circuit board comprising a prepreg and/or a laminate, wherein said prepreg and/or laminate comprises any one of the flame retardant compositions described herein.

Partial curing as used herein can comprise any level of curing, short of complete cure, and will vary widely depending on the specific materials and conditions of manufacture as well as the desired end-use applications. In one specific embodiment, the article herein can further comprise a copper foil. In one embodiment the article can comprise a printed circuit board. In one embodiment there is provided an FR-4 laminate which comprises a prepreg and/or laminate of the invention. In a more specific embodiment there is provided a printed circuit board comprising an FR-4 laminate, wherein the FR-4 laminate comprises a prepreg or laminate of the invention.

In one embodiment herein there is provided a process for making a laminate that contains any of the flame retardant compositions described herein, which process comprises impregnating the respective composition(s) into a filler material, e.g., a glass fiber mat to form a prepreg, followed by processing the prepreg at an elevated temperature and/or pressure to promote a partial cure to a B -stage and then laminating two or more of said prepregs to form said laminate. In one embodiment, said laminate and/or prepreg can be used in the applications described herein, e.g., printed circuit boards. It is provided herein, that any of the compositions described herein are useful for making a prepreg and/or laminate with a good balance of laminate properties and thermal stability, such as one or more of high T_g (i.e. above 130°C), a Tdof 330°C and above, a t₂88 of 5 minutes and above, a flame resistance rating of V-0, good toughness, and good adhesion to copper foil. In recent years the Td has become one of the most important parameters, because the industry is changing to lead-free solders which melt at a higher temperature than traditional tin-lead solders.

In one embodiment herein, the flame retardant compositions described herein can be used in other applications, e.g., encapsulants for electronic elements, protective coatings, structural adhesives, structural and/or decorative composite materials, in amounts as deemed necessary depending on the particular application.

Examples:

Preparative Example 1

Synthesis of DOPO-HQ-Diacetate-Isophthaloyl-Polyester (compound I)

A 0.25 L 4-necked flask, equipped with a mechanical stirrer, a thermometer and a nitrogen inlet, was charged with DOPO-HQ-Diacetate (106 g, 0.26 mol) and heated to 170 °C to full melting. Isophthalic acid (43 g, 0.26 mol) and potassium acetate 0.3 g were added and the reaction mixture was heated at 280°C for 2 h without vacuum and 1 h with vacuum of 30 mbar. As the reaction continued, the mixture became more viscous. During the entire reaction the acetic acid formed was distilled out of the reaction zone to accelerate the polycondensation. The resulting, very viscous, hot liquid product was quickly poured onto an aluminum plate to avoid

solidification in the flask. The final solid light-brown product was obtained in a quantitative yield. The product contained 2.8% DOPO-HQ-monoacetate and DOPO-HQ-acetate-isophthalate, 2.2% unreacted DOPO-HQ-Diacetate and 95% higher molecular weight oligomers (HPLC area %). The phosphorus content in the product was 6.1%. GPC analysis in DMF showed the Mw of 32610 g/mol and Mn of 13360 g/mol. The product did not dissolve in MEK at 60°C over a period of 3 h. Inherent viscosity of the product in DMF was 0.32 dL/g. Preparative Example 2

Synthesis of DOPO-HQ-Diacetate-Terephthaloyl-Polyester (compound II)

A 0.25 L 4-necked flask, equipped with a mechanical stirrer, a thermometer and a nitrogen inlet, was charged with DOPO-HQ-Diacetate (106 g, 0.26 mol) and heated to 170 °C to full melting. Terephthalic acid (43 g, 0.26 mol) and potassium acetate 0.3 g were added and the reaction mixture was heated at 240°C for 2 h without vacuum and 1 h with vacuum of 30 mbar. As the reaction continued, the mixture started to solidify. During the entire reaction the acetic acid formed was distilled out of the reaction zone to accelerate the polycondensation. The final solid off-white product was obtained in a quantitative yield. The phosphorus content in the product was 6.2%. The product did not dissolve in organic solvents.

Solubility test at 25 °C:

Table 1: Materials

Example 1-8: Small scale Resin Curing Experiments with Flame Retardant of the invention

Samples of (a) compound I were combined with (b) PPE resin and (c) crosslinking agent and cured on a small scale. Compositions of small-scale samples are shown in Table 2. Total % P was 2.1-2.3%. The sample was cured at 177-182 °C for 2 hours and post-cured at 190-197 °C for 1 hour. Thermal stability of the samples was studied using DSC and TGA. To prepare varnish castings for Dk and Df measurements, components in Table 2 were blended in solvent (Acetone or Toluene). The mixture was dried under vacuum, followed by molding and curing at 177-182 °C for 2 hours and post-curing at 190-197°C for 1 hour. The results are shown in the Table 3: Table 2: Composition for small scale curing experiments

Table 3: Tg, TGA, Dk and Df results for small scale curing experiments

Discussion: As shown in Table 3, the Examples 1 and 2 of the present invention have very low dielectric constant (Dk) and loss factor (Df) which are close to the Comparative Example 3 without flame retardant. While the presence of the flame retardant helps in passing flammability test, it does not impair the excellent dielectric properties of the formulation. When PPE resin is removed from the formulation, the thermoset sample cannot pass flammability test (Comparative Example 4).

While the invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

Claims:

1. A flame retardant composition comprising:

(a) a compound having the general formula (I):

which has a weight average molecular weight of from about 1,000 to about 700,000, and where X is a bivalent aromatic hydrocarbon group containing from 6 to about 12 carbon atoms, which may optionally be substituted with an alkyl group or an alkoxyl group each containing up to about 6 carbon atoms,

where Z is selected from the group consisting of a covalent bond, -SO2-, -C(CH₃)2-, -CH(CH₃)-, and -CH2-; a is an integer of from 0 to 2; b is an integer of from 0 to 2, and

wherein the wavy lines of each structure of Y indicate the bonds to the oxygen atoms which Y bridges in the general formula (I); l group of from 1 to about 4 carbon

where R² is selected from the group consisting of H or -C(=0)R³ and where R³ is selected from an alkyl group of from 1 to 4 carbon atoms, a phenyl group, a napthyl group and an aromatic phenol group which is selected from one of a phenol group, o-cresol group, m-cresol group, /?-cresol group, a-naphthol group, and a ?-naphthol group,

and when R² is H, R¹ cannot be phenyl or naphtyl,

and n is >2; and,

(b) a polyphenylene ether and/or an oligomer thereof.

(c) a crosslinking agent having a carbon-carbon unsaturated double bond laim 1 wherein R¹ is

is a bivalent aromatic hydrocarbon group of 6 to 12 carbon atoms which is optionally substituted with an alkyl or alkoxy group of up to 6 carbon atoms.

3. The flame retardant composition of Claim 1 wherein R¹ is an alkyl of from 1 to about 4 carbon atoms and where X is a bivalent aromatic hydrocarbon group of from 6 to 12 carbon atoms which is optionally substituted with an alkyl or alkoxy group of up to 6 carbon atoms.

4. The flame retardant composition of Claim 1 wherein X is a bivalent aromatic

hydrocarbon group of from 6 to 12 carbon atoms which is optionally substituted with an alkyl or alkoxy group of up to 6 carbon atoms.

5. The flame retardant composition of Claim 1 wherein n is from 2 to about 100.

6. The flame retardant composition of Claim 1 wherein the polyphenylene ether (b) is a linear polyphenylene ether that is independently terminated on each end with either a vinyl group or an allyl group.

7. The flame retardant composition of Claim 1 wherein the polyphenylene ether (b) is of the eneral formula (II):

wherein Zi is a divalent moiety derived from compounds selected from the group consisting of bisphenol A, bisphenol F, bisphenol S, naphthalene, anthracene, biphenyl, tetramethyl biphenyl, phenol novolac, cresol novolac, bisphenol A novolak, and borane compounds, and mi and m₂ are each independently an integer of from about 3 to about 20.

8. The flame retardant composition of Claim 1 wherein the polyphenylene ether (b) has number average molecular weight of from 1,000 to 10,000.

9. The flame retardant composition of Claim 1 wherein the polyphenylene ether (b) has number average molecular weight of from 1,000 to 3,000.

10. The flame retardant composition of Claim 1 further comprising a thermosetting resin in an amount of from about 1% by weight to about 25 % by weight.

11. The flame retardant composition of Claim 10 wherein the thermosetting resin is an epoxy resin.

12. The flame retardant composition of Claim 10 wherein the thermosetting resin is an epoxy resin selected from the group consisting of halogen-free epoxies, phosphorus -free epoxies, and phosphorus-containing epoxies and mixtures thereof.

13. Any one of a coating formulation, an encapsulant, a composite, an adhesive, a molding a bonding sheet or a laminated plate comprising the composition of Claim 1.

14. The flame retardant composition of Claim 1 wherein the composition is halogen-free.

15. An article comprising the composition of Claim 1.

16. The article of Claim 15 wherein said article can be used in lead free soldering

applications and electronic devices.

17. The article of Claim 15 wherein the article further comprises a copper foil.

18. The article of Claim 15 wherein said article is a printed circuit board.

19. A prepreg comprising the flame retardant composition of Claim 1.

20. A laminate or a bonding sheet comprising the flame retardant composition of Claim 1.

21. A printed wiring board comprising prepreg of Claim 19.

22. A printed wiring board comprising the laminate of Claim 20.

23. A process of making a laminate that contains the composition of Claim 1 comprising impregnating the composition into a filler material, to form a prepreg, followed by processing the prepreg at elevated temperature to promote partial cure to a B-stage and then laminating two or more of said prepregs at elevated pressure and temperature to form a laminate.

24. A printed circuit board made by the process of Claim 23.

25. The flame retardant composition of Claim 1 wherein the crosslinking agent having a carbon-carbon unsaturated double bond (c) is selected from the group consisting of a

hydrocarbon crosslinking agent (1), a crosslinking agent (2) containing at least three functional groups, a rubber (3) having a block or random structure, and combinations thereof.

26. hydrocarbon crosslinking agent (1) is selected from the group consisting of butadienes; polybutadienes, octadienes, polyoctadienes, decadienes, polydecadienes, vinylcarbazole and combinations thereof.

27. The flame retardant compositon of Claim 25 wherein the crosslinking agent containing three or more functional groups (2) is selected from the group consisting of triallyl isocyanurate, 1,2,4-trivinylcyclo 1,2,4-trivinyl cyclohexane (TVCH), and combinations thereof.

28. The flame retardant composition of Claim 25 wherein the rubber (3) having a block or random structure is selected from the group consisting of styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylate-butadiene rubber, acrylonitrile-butadiene-styrene rubber, and combinations thereof.