Heat-hardenable compositions based on polyglycidyl ethers and polyhydric phenols, halogenated tetraphenols, polyglycidyl ethers and process for preparing tetraphenols

Abstract: Heat-hardenable compositions comprising mixtures of a) at least a polyglycidyl ether of a tetraphenol having on average at least three epoxy groups per molecule, and b) at least a tetraphenolic crosslinking agent, in a weight ratio sufficient to provide an epoxy group to phenolic hydroxyl group equivalent ratio in the range of from 0.5 to 1.5, and wherein the tetraphenol from which the polyglycidyl ether is derived and the tetraphenolic crosslinking agent are represented by the general formula wherein R¹ and R² are H or a C₁₋₃ alkyl group, R³ is a linear C₂₋₆ alkylene group which may carry one or more alkyl substituents, each n individually is 0,1 or 2 and X is Cl or Br. The heat-hardenable compositions are used in the preparation of laminates, such as in printed circuit boards, which require high thermal stability.

Description: The present invention relates to heat-hardenable compositions comprising mixtures of polyglycidyl ethers and polyphenolic crosslinking agents and to their use in the production of laminated products. Laminates generally comprise a reinforcing material of which different layers are bonded together via a hardened thermosetting binder composition. A conventional method for making such laminates is to impregnate a glass fibre fabric with an epoxy binder system followed by compression moulding one or more layers of the impregnated fabric. A primary requirement for such binder compositions is that they have good bonding properties. A further requirement especially for those laminates which are used in the production of printed circuit boards, is that the crosslinked binder matrix should have a good thermal stability. It has long been established that polyfunctional epoxy resin based binder systems are well suited to be used in the production of laminates. Examples of such epoxy resin based binders are described in US A 3,218,370 and comprise a combination of 1) a polyglycidyl ether having an epoxy functionality of at least three, derived from a polyphenol having from three to four phenylol groups in its molecule which are connected via an aliphatic hydrocarbon group, and 2) a stoichiometric amount of a phenolformaldehyde condensate, having a phenolic hydroxyl functionality of at least three. Those known laminates will meet most of the heat stability requirements for conventional printed circuit boards. However, with the advent of more sophisticated printed circuit boards which are based on thinner metal conductive strips and which have a larger number of such strips per unit surface area, the thermal stability of the binder matrices from the prior art may not always be sufficient. Hence, there is a growing demand for heat-hardenable binder compositions for use in the production of laminates having increased thermal stability. A criterion frequently employed when selecting novel heat-hardenable binder systems, e.g for use in laminates, is the glass transition temperature (Tg) of the hardened binder system, as this gives an indication of the stability of the matrix to withstand processing, e.g soldering at 260 °C. The Tg is also taken as a criterion for the dimensional stability in the processing temperature range. The problem underlying the present invention is to provide heat-hardenable binder systems for use in laminate production which have improved thermal stability or alternatively a higher Tg than existing systems. It has now been found that this problem can be solved by providing heat-hardenable compositions comprising mixtures of a) at least a polyglycidyl ether of a tetraphenol having on average at least three epoxy groups per molecule, and b) at least a tetraphenolic crosslinking agent in a weight ratio sufficient to provide an epoxy group to phenolic hydroxyl group equivalent ratio in the range of from 0.5 to 1.5, and wherein the tetraphenol from which the polyglycidyl ether is derived and the tetraphenolic crosslinking agent are represented by the general formula wherein R¹ and R² are H or a C₁₋₃ alkyl group, R³ is a linear C₂₋₆ alkylene group which may carry one or more alkyl substituents, each n individually is 0,1 or 2 and X is Cl or Br. Preferred heat-hardenable compositions are those wherein in general formula I R¹ and R² are H. Especially preferred are such compositions wherein in general formula I R³ is a linear propylene group. The tetraphenols of general formula I from which the polyglycidyl ethers are derived and on which the tetraphenolic crosslinking agents are based and which may be employed in the heat-hardenable compositions of the present invention include: 1,1,4,4-tetrakis(hydroxyphenyl) butane,. 1,1,5,5 tetrakis(hydroxyphenyl) pentane, 1,1,5,5-tetrakis(hydroxyphenyl)-3-methyl pentane, 1,1,5,5-tetrakis(3-bromo-4-hydroxyphenyl) pentane, 1-(3-chloro-4-hydroxyphenyl)-1,5,5 tris(4-hydroxyphenyl) pentane, 1-(3-bromo-2-hydroxyphenyl)-1,5,5-tris(3-bromo-4-hydroxyphenyl) pentane, 1,1,5,5-tetrakis(3,5-dibromo-4-hydroxyphenyl) pentane, 2,2,9,9-tetrakis(hydroxyphenyl) decane. The heat-hardenable compositions of the present invention are based on well defined compounds which can conveniently be prepared on a commercial scale. Furthermore the hydrocarbon group connecting the phenylol groups of the tetraphenol of general formula I, affords good solubility of the individual compounds in combination with a high glass transition temperature and good mechanical performance properties of the hardened compositions. Finally those compositions wherein in general formula I n / O have improved flame retardancy upon hardening. With the tetraphenols of general formula I the phenolic hydroxyl groups will generally occupy the para or an ortho position with respect to the hydrocarbon substituent group. Preferred however are tetraphenols of general formula I wherein the phenolic hydroxyl groups predominantly occupy the para position. The tetraphenols of general formula I, wherein R¹ and R² are H and each n is O, can readily be obtained by condensing a linear C₄₋₈ dialdehyde with phenol following the method as described e.g. in US-A 2,806,016. A disadvantage of said method is that it requires a reaction time of several days. A preferred method for the preparation of such tetraphenols from the same reactants comprises reacting phenol and a linear C₄₋₈ dialdehyde in the presence of hydrochloric acid, characterized in that the molar ratio of phenol and dialdehyde is at least 10:1 and that the hydrochloric acid is present in a concentration of at least 0.5 % mol calculated on phenol intake, and the dialdehyde is gradually added as an aqueous solution to the mixture of molten phenol and hydrochloric acid at such a rate that the temperature in the reactor does not rise above 65 °C. and wherein subsequently the volatiles are removed by distillation at elevated temperature and subatmospheric pressure. Upon completion of the dialdehyde addition it is beneficial to allow for a relatively short post-reaction period, e.g. 30 minutes at approximately 50 °C. By this method the envisaged tetraphenol may be obtained in yields which are well above 85 % m. The tetraphenols of general formula I wherein R¹ and R² are a C₁₋₃ alkyl group, can be prepared via a process wherein phenol is reacted with an appropriate linear C₈₋₁₂ diketone in the presence of a hydrochloric acid/mercaptan catalyst system. The chlorine or bromine containing tetraphenols of general formula I can be obtained by reaction of the corresponding halogen-free tetraphenol with chlorine or bromine respectively, via methods well known in the art. Said halogen groups will usually be substituted on the ortho positions of the phenyl rings with respect to the phenolic hydroxyl group, although configurations wherein such a halogen group occupies the para position with respect to the phenolic hydroxyl group may also occur when said phenolic hydroxyl group occupies an ortho position with respect to the hydrocarbon substituent. Preferred however are such halogenated tetraphenols wherein the groups X predominantly occupy an ortho position with respect to the phenolic hydroxyl group. The value for n in general formula I will be determined by the molar excess of chlorine or bromine employed in the halogenation process step. The tetraphenols of general formula I wherein R¹ and R² are H or a C₁₋₃ alkyl group, R³ is a C₂₋₃ linear alkylene group, n in at least one of the four phenylol entities is 1 or 2 and X is Cl or Br, are novel compounds. The polyglycidyl ethers which may be employed in the heat-hardenable compositions of the present invention can be prepared according to the method as described in US-A 3.452.116. It is preferred however, to prepare these polyglycidyl ethers based on the tetraphenols of general formula I via a process wherein the tetraphenol is dissolved in a large molar excess, with respect to the intake of phenol hydroxyl, of an epihalohydrin preferably epichlorohydrin, and 2-propanol. The solution is heated to a temperature in the range of from 40 to 50 °C whereupon a 15 to 50 % m aqueous sodium hydroxide solution is added over a period of about 30 minutes, in an amount which is sufficient to provide a slight molar excess of sodium hydroxide with respect to the phenol hydroxyl intake, and in which period the temperature is allowed to increase to a temperature in the range of from 60 to 70 °C. After a short post reaction time (30 -60 min) at that temperature the organic phase is separated off, washed and dissolved in a suitable, partly water-miscible solvent such as methyl isobutyl ketone and further treated with a small amount of approximately a 4-6 % m aqueous sodium hydroxide solution at the reflux temperature of the water and methyl isobutyl ketone. After a further washing step and removal of the volatiles in vacuo the polyglycidyl ethers are obtained as a pale yellow solid material. Preferred such polyglycidyl ethers have on average 3.8 to 4.0 epoxy groups per molecule. Polyglycidyl ethers having at least three epoxy groups per molecule and which are derived from the tetraphenols of general formula I wherein R¹ and R² are H or a C₁₋₃ alkyl group, R³ is a C₂₋₃ linear alkylene group, n in at least one of the four phenylol entities is 1 or 2 and X is Cl or Br, are novel compounds. The polyglycidyl ethers which may be employed in the heat-hardenable compositions of the present invention may be chosen from single polyglycidyl ethers as herein before defined or from mixtures of such polyglycidyl ethers, e.g mixtures of polyglycidyl ethers having a different degree of halogenation or different halogen atoms. The tetraphenol crosslinking agent which may be used in the heat-hardenable compositions of the present invention may be a single tetraphenol as hereinbefore defined or a mixture of such tetraphenols e.g mixtures of tetraphenols having a different degree of halogenation or different halogen atoms. It is preferred that the polyglycidyl ether(s) and the tetraphenol crosslinking agent(s) are present in the heat-hardenable composition of the present invention in a weight ratio which is sufficient to provide an epoxy group to phenolic hydroxyl group equivalent ratio in the range of from 0.8 to 1.2. Although the heat-hardenable compositions may be hardened as such by heating at an elevated temperature it has been found beneficial to incorporate small amounts of a catalyst which promotes the hardening reaction between the polyglycidyl ether and the tetraphenol crosslinking agent. Suitable catalysts may be selected from the group of catalysts comprising tertiary amines, quarternary ammonium salts, quarternary phosphonium salts, tertiary sulfonium salts, imidazoles and Lewis acids. The actual amount of catalyst to be employed will be determined by the nature of the catalyst as well as the hardening conditions and will generally be in the range of from 0.001 - 1.0 % m on total solids of the composition. The heat-hardenable compositions of the present invention may conveniently be hardened at a temperature in the range of from 150 to 250 °C and preferably from 180 to 220 °C. When a heat hardenable composition of the present invention is employed for the preparation of laminates it is dissolved in a solvent to facilitate the impregnation of the reinforcement, such a glass fibre fabric. The nature of the solvent is not critical provided said solvent is inert. It is preferred however, to employ solvents with a high solvent power and a low boiling point so that only relatively small amounts of solvents have to be employed in preparing the impregnation solution. This also enables fast solvent evaporation from the impregnated fabric. Suitable solvents include organic esters, ketones, mixtures of alcohols and selected hydrocarbons. Ketones are preferred. If desired, pigments, fillers, surface active agents, stabilisers, antioxidants and other auxiliary compounds may also be included in the heat-hardenable composition of the present invention. The invention will be further illustrated by the following examples. Example I Preparation of tetraphenylol pentane Phenol (1128 g, 12 mol) was melted in a nitrogen-flushed glass reactor at 47 °C which was followed by the addition of concentrated (37 % m) hydrochloric acid (11.8g, 4.4 g HCl). Glutaraldehyde (160 g of a 50 % m aqueous solution, 0.8 mol) was added with stirring over a period of 0.5 h during which the temperature in the reactor was allowed to increase to a maximum of 55 °C. After a post-reaction period of 15 min. at 50 °C the volatiles were removed in vacuo (160 °C/17 mbar) yielding 330 g of tetraphenylol pentane (94 % yield). The end product melted between 110 and 120 °C, had a phenolic hydroxyl content of 9100 mmol/kg and was found to contain less than 0.5 % m phenol. Example II Preparation of brominated tetraphenylol pentane Tetraphenylol pentane (220 g, 0.5 mol) as prepared in example I was dissolved in a blend of dichloro methane (450 ml) and methanol (150 ml). The solution was cooled to -35 °C and maintained at that temperature while bromine (320 g, 2 mol Br₂) was added with stirring over a period of two hours. Subsequently the temperature was raised to 20 °C and the solution was washed with an aqueous sodium bicarbonate solution until neutral which was followed by evaporation of the volatiles in vacuo (120 °C, 2 mbar). The brittle brownish product (375 g) melted at a temperature between 70 - 80 °C and had a phenolic hydroxyl of 5300 mmol/kg and a bromine content of 42.3 % m. Example III Preparation of polyglycidyl ether from brominated tetraphenylol pentane Brominated tetraphenylol pentane (302 g, 0.4 mol) as prepared in example II was dissolved in a blend of epichlorohydrin (740 g, 8 mol) and 2-propanol (336 g). The solution was heated to 45 °C whereupon an aqueous solution of sodium hydroxide (68,8 g NaOH in 73 g water) was added over a period of 30 minutes with stirring in which time the temperature was raised to 70 °C. After a post-reaction period of 15 minutes the organic phase was separated from the brine and washed with a 3 % m NaH₂PO₄ solution (250 ml) and water (250 ml). After removal of the volatiles at 100 °C and 20 mbar the residue (400 g) was dissolved in methyl isobutyl ketone (600 g) and treated with a 5 % m aqueous NaOH solution (60 g) for 1.5 hours at 90 °C. After a further washing with a 3 % m aqueous NaH₂PO₄ solution (250 ml) and water (250 ml) the solvent was stripped off in vacuo (120 °C, 2 mbar). The final product was a pale yellow slightly tacky epoxy resin (385 g) having an epoxy group concentration: 3610 mmol/kg, a saponifiable chlorine content: 65 ppm and a bromine content: 32.7 % m. Example IV Preparation of polyglycidyl ether from tetraphenylol pentane Tetraphenylol pentane (220 g, 0.5 mol) as prepared according to the method of Example I was dissolved in a blend of epichlorohydrin (1110 g, 12 moles), 2-propanol (660 g, 11 moles) and water (171 g, 9.5 moles). The solution was heated to 40 °C whereupon a 20 % m aqueous sodium hydroxide solution (440 g, 2.2 moles NaOH) was added with stirring over a period of one hour. During the addition, the temperature was gradually increased to 70 - 71 °C. After a post reaction of 45 minutes at 70 - 71 °C the organic phase was separated from the aqueous brine and washed consecutively with 350 ml each of a 3 % m NaH₂PO₄ solution and water. Subsequently the volatiles were removed in vacuo (100 °C, 20 mbar) and the residue (320 g) was dissolved in methyl isobutyl ketone (900 g) and mixed with a 5 % m aqueous NaOH solution (400 g) at 90 °C for one hour. The organic phase was separated off, washed with 350 ml each of a 3 % m aqueous NaH₂PO₄ solution and water, which was followed by stripping the solvent in vacuo (140 °C, 10 mbar) during 3 hours. The final product was a pale yellow, slightly tacky epoxy resin having an epoxy group concentration: 5440 mmol/kg, saponifiable chlorine content: 90 ppm. Examples V - VIII Laminate preparation Heat-hardenable compositions based on stoichiometric blends (i.e blends having an epoxy/phenolic hydroxyl equivalent ratio 1) of at least a polyglycidyl ether and at least a tetraphenylol pentane as prepared following examples I to IV were employed to prepare laminates. To this end said compounds were dissolved in methyl ethyl ketone in amounts as indicated in Table 1 hereinafter, which table also gives the amounts of ethyl triphenyl phosphonium iodide (ETPPI) catalyst which was added to each of the solutions obtained. The reactivity of said blends was determined by measuring the time to gelation at 180 °C of said solutions. The laminates were prepared by impregnating pieces of glass fibre fabric with the solutions and after drying at 20 °C for 40 minutes the impregnated pieces of fabric were cured at 180 °C for 1 hour followed by 30 minutes at 215 °C. The Tg of the laminates thus prepared was determined by Differential Scanning Calorimetry. Gelation times and Tg values are shown given in Table 1. Comparative Experiment Following the procedure as in examples V -VIII, a laminate based on a stoichiometric blend of a polyglycidyl ether as prepared following example III and a commercial novolac resin (ALNOVOL SPN 981 ex HOECHST) was also prepared and evaluated. The laminate composition the gelation time and the Tg value have been included in Table 1.

Claims: Claims for the following Contracting States : AT, BE, CH, DE, DK, FR, GB, GR, IT, LI, LU, NL, SE Heat-hardenable compositions comprising mixtures of a) at least a polyglycidyl ether of a tetraphenol having on average at least three epoxy groups per molecule, and b) at least a tetraphenolic crosslinking agent, in a weight ratio sufficient to provide an epoxy group to phenolic hydroxyl group equivalent ratio in the range of from 0.5 to 1.5, and wherein the tetraphenol from which the polyglycidyl ether is derived and the tetraphenolic crosslinking agent are represented by the general formula wherein R¹ and R² are H or a C₁₋₃ alkyl group, R³ is a linear C₂₋₆ alkylene group which may carry one or more alkyl substituents, each n individually is 0,1 or 2 and X is Cl or Br. Compositions as claimed in claim 1, wherein in general formula I R¹ and R² are H. Compositions as claimed in claim 2, wherein in general formula I R³ is a linear propylene group. Compositions as claimed in any one of claims 1-3, wherein in general formula I the phenolic hydroxyl groups predominantly occupy the para position with respect to the hydrocarbon substituent. Compositions as claimed in any one of claims 1-4, wherein in general formula I the groups X predominantly occupy an ortho position with respect to the phenolic hydroxyl groups. Compositions as claimed in any one of claims 1-5, wherein the polyglycidyl ether has on average from 3.8 to 4.0 epoxy groups per molecule. Compositions as claimed in any one of claims 1-6, wherein the weight ratio of polyglycidyl ether and tetraphenolic crosslinking agent is sufficient to provide an epoxy group to phenolic hydroxyl group equivalent ratio in the range of from 0.8 to 1.2. A process for the preparation of tetraphenols having the general formula wherein R³ is a linear C₂₋₆ alkylene group which may carry one or more alkyl substituents, by reaction of phenol and a linear C₄₋₈ dialdehyde in the presence of hydrochloric acid, characterized in that the molar ratio of phenol and dialdehyde is at least 10:1 and that the hydrochloric acid is present in a concentration of at least 0.5 % mol calculated on phenol intake, and the dialdehyde is gradually added as an aqueous solution to the mixture of molten phenol and hydrochloric acid at such a rate that the temperature in the reactor does not rise above 65 °C, and wherein subsequently the volatiles are removed by distillation at elevated temperature and subatmospheric pressure. Process for the preparation of chlorinated or brominated tetraphenols by the process as claimed in claim 8 followed by chlorination or bromination. Claims for the following Contracting State : ES A process for the preparation of heat-hardenable compositions by blending a) at least a polyglycidyl ether of a tetraphenol having on average at least three epoxy groups per molecule, and b) at least a tetraphenolic crosslinking agent, in a weight ratio sufficient to provide an epoxy group to phenolic hydroxyl group equivalent ratio in the range of from 0.5 to 1.5, and wherein the tetraphenol from which the polyglycidyl ether is derived and the tetraphenolic crosslinking agent are represented by the general formula wherein R¹ and R² are H or a C₁₋₃ alkyl group, R³ is a linear C₂₋₆ alkylene group which may carry one or more alkyl substituents, each n individually is 0,1 or 2 and X is Cl or Br. A process as claimed in claim 1, wherein in general formula I R¹ and R² are H. A process as claimed in claim 2, wherein in general formula I R³ is a linear propylene group. A process as claimed in any one of claims 1-3, wherein in general formula I the phenolic hydroxyl groups predominantly occupy the para position with respect to the hydrocarbon substituent. A process as claimed in any one of claims 1-4, wherein in general formula I the groups X predominantly occupy an ortho position with respect to the phenolic hydroxyl groups. A process as claimed in any one of claims 1-5, wherein the polyglycidyl ether has on average from 3.8 to 4.0 epoxy groups per molecule. A process as claimed in any one of claims 1-6, wherein the weight ratio of polyglycidyl ether and tetraphenolic crosslinking agent is sufficient to provide an epoxy group to phenolic hydroxyl group equivalent ratio in the range of from 0.8 to 1.2. A process for the preparation of tetraphenols having the general formula wherein R³ is a linear C₂₋₆ alkylene group which may carry one or more alkyl substituents, by reaction of phenol and a linear C₄₋₈ dialdehyde in the presence of hydrochloric acid, characterized in that the molar ratio of phenol and dialdehyde is at least 10:1 and that the hydrochloric acid is present in a concentration of at least 0.5 % mol calculated on phenol intake, and the dialdehyde is gradually added as an aqueous solution to the mixture of molten phenol and hydrochloric acid at such a rate that the temperature in the reactor does not rise above 65 °C, and wherein subsequently the volatiles are removed by distillation at elevated temperature and subatmospheric pressure. Process for the preparation of chlorinated or brominated tetraphenols by the process as claimed in claim 8 followed by chlorination or bromination.

Inventors: DE KRUIF JAN HENDRIK, RAUDENBUSCH WERNER THEODOR, VAN ACKER EDUARD M A A J, VERBURG ANTOON, DE KRUIF, JAN HENDRIK, RAUDENBUSCH, WERNER THEODOR, VAN ACKER, EDUARD M. A. A. J., VERBURG, ANTOON
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1988
Main classification: C08G59
IPC codes: C07B61, C08G59, C07C39, B01J27, C07C67, C07C27, C07D303, C07C37, H05K1