Process for producing modified phenolic resins

Abstract

 A drying oil, for example isomerized linseed oil or dehydrated castor oil, which has an iodine value of 140 or more and a content of conjugated double bonds of less than 50% is reacted with isopropenylphenol and/or at least one oligomer thereof in an amount, by weight, generally of 0.1 - 2 times as great as that of the drying oil in the presence of a small amount of an acid preferably at a temperature of 65 -150 °C for 0.5 - 3 hours to modify the oil. By the modifying reaction, isopropenylphenol and/or its oligomer(s) is/are introduced into the drying oil while leaving the double bonds of the oil as they are. The thus modified oil is further reacted with a phenol or phenols under strongly acidic conditions to introduce therein one or more phenols to further modify the oil, The further modified drying oil serving as a phenolic component or a part thereof is then reacted with formladehyde or a compound based on formaldehyde to give a modified phenolic resin. This modified phenolic resin is useful for making a phenolic laminate with improved flexibility, punching quality and waterproofness.

Description

[0001] This invention relates to a process for producing a modified phenolic resin by reacting in the presence of an acidic catalyst a phenolic modified drying oil and formaldehyde.

[0002] It is well known that phenolic laminates can be obtained by impregnating substrates with a resol-type phenolic resin obtained by interacting a phenol such as phenol, cresol, xylenol or the like and formaldehyde, and superposing these substrates under heating and pressurizing conditions. The obtained laminate has industrially wide utility in the field of electric insulating materials and structural materials. In recent years, the laminate has particularly received much greater application to electric and electronic instruments. Since parts of these instruments have become simpler to assemble, more compact and higher in performance, there is a strong and growing demand for laminates which have excellent electrical insulating property and resistances to heat and alkali with balanced mechanical strengths and punching quality.

[0003] In particular the laminate of the type mentioned above is being applied as printed circuits to a very large extent and, in this field, it is used by punching in desired forms. In general, however, the phenolic resin is so hard and brittle that, upon punching, the resin-impregnated laminate must be processed under heating conditions of 100 - 150°C, with the attendant disadvantage that the punched article invariably involves undesirable variation in size due to its expansion and contraction during the process and warp due to residual stress. In addition, the heating step is troublesome. In order to overcome these disadvantages, there have been proposed several methods for making phenolic laminates.

[0004] In order to improve the punching quality, for example, it is known from old to use a modified phenolic resin treated with a drying oil such as tung oil which contains a large amount of conjugated double bonds. However, through the punching quality can be surely improved by the modification due to the mere addition of the drying oil, other properties or strengths remain very poor.

[0005] Accordingly, there has been proposed another method in which the drying oil is further modified That is, the drying oil containing a large amount ol conjugated double bonds is reacted with phenols under acidic conditions, followed by further reaction with formaldehyde. By such modification, the punching quality can be improved while increasing the crosslinking density of the impregnated modified phenolic resin to prevent lowering of other characteristic properties. In this method, it is essential to use tung oil which contains a large amount of conjugated double bonds and which has great chemical
reactivity with phenols. Chinese tung oil has, for example, the following fatty acid composition: 81.5% of a-eleastearic acid; 6.7 % of linoleic acid; 6.4 % of oleic acid; 2.9 % of stearic acid; and 2.5 % of palmitic acid. Since tung oil thus contains 80 % or more nf conjugated double bonds in the main chain thereof, it is readily reacted with phenols in the presence of an acidic catalyst.

[0006] However, even though the phenol-modified tung oil is used to make a laminate, the laminate still remains poor in inter-laminar strength and thus tends to delaminate. This is due to a fact that since the reaction of tung oil and a phenol in the presence of an acidic catalyst is the Friedel-Crafts reaction which proceeds under severe conditions, polymerization of tung oil inevitably takes place during the reaction and it is hard to impregnate a substrate with the resulting resin. A laminate using such modified resin is unsatisfactory for use for small-sized, precise parts.

[0007] Instead of using tung oil, consideration may be given to the application, to the above method, of other drying oils such as isomerized linseed oil, dehydrated castor oil, tall oil, and perilla oil, which have high content of non-conjugated double bonds and low content of conjugated double bonds. However, this is very difficult and the reason for this will be described with reference to the use of dehydrated castor oil. Dehydrated castor oil is a glyceride of linoleic acid which is obtained by dehydrating ricinoleic acid (a main component of castor oil), and has the following fatty acid composition: 29 % of conjugated linoleic acid, 58 % of non-conjugated linoleic acid; 7.5 % of oleic acid; 5.0 % of ricinoleic acid; and 0.5 % of palmitic acid and stearic acid. This drying oil having such low content of conjugated double bonds is weaker in chemical reactivity than those having a higher content of conjugated double bonds. If these drying oils having a low content of conjugated double bonds are used instead of tung oil to conduct the above method, introduction of phenols into these pils become insufficient. When appllied ior making a faminate, the modified resin does not undergo a satisfactiry crosslinking reaction, making it difficult to produc a laminate with excellent electrical and mechanical properties, sufficient resistance to chemicals, and moisture and which is waterproof.

[0008] Introduction of phenols into drying oils with low chemical reactivity and have a low content of conjugated double bonds is described in Japanese Patent Publication No. 45 - 35918. In this method, dehydrated castor oil i= reacted with phenol in the presence of a sulphuric acid catalyst at an elevated temperature. However, this method is accompanied by a difficulty that since a large amount of sulphuric acid is used as the catalyst, Glauber's salt produced by neutralization of the acid impairs the moisture- resistance and waterproofness and electrical properties of the resulting laminates.

[0009] It is therefore an object of the present invention to provide a process for modifying a drying oil, which has a low content of conjugated double bonds and has low chemical reactivity, by reaction with phenols to give a phenol-modified oil which is effective in improving the properties of a phenolic resin produced therefrom, and to provide a modified phenolic resin using the modified drying oil, the phenolic resin being useful in making a laminate which exhibits good punching quality, electrical characteristics moisture- resistance and waterproofness, chemical resistance andand mechanical properties.

[0010] According to the present invention there is provided a process for producing a modified phenolic resin by reacting a phenolic component and formaldehyde or a compound based on formaldehyde, the phenolic component consisting at least in part, of a phenolic modified drying oil, characterised in that the drying oil (i) used is a drying oil having an iodine value of 140 or more and a content of conjugated double bonds of less than 50 % and the drying oil (I) is reacted with isopropenylphenol and/or at least one oligomer thereof in the presence of an acidic catalyst and in the presence or absence of at least one phenol (V) to form a first phenolic modified drying oil (II) that the modified drying oil (II) is further reacted with at least one phenol (VI) in the presence of an acidic catalyst 1o form a further phenolic modified drying oil (III) and that the further modified drying oil (III) is used as or as part of a phenolic component (VII) which is reacted with formaldehyde or a compound based on formaldehyde to produce a modified phenolic resin (IV).

[0011] The term "drying oil" as used for the purposes of the present invention means a drying oil chosen from drying oils of plant and animal origins which have an iodine value of 140 or more and in which the content of unsaturated fatty acids having conjugated double bonds is less than 50 % of a total of fatty aci which constitute the drying oil, and also synthe drying oils which are obtained by treating play animal oils by a suitable means such as isomerization, dehydration or distillation and extraction. The "unsaturated fatty acids having conjugated double bonds" means conjugated linoleic acid, isomerized conjugated linoleic acid, isomerized conjugated lindenic acid and the like. Examples of drying oils having an iodine value of 140 or more and a content of conjugated double

referred to simply as drying oils) include isomerized linseed oil, dehydrated castor oil, tall oil, linseed oil, perilla oil, safflower oil, hempseed oil, sardine oil, cuttlefish oil and the like.

[0012] The isomerized linseed oil means a triglyceride of fatty acids of conjugated linseed oil which is obtainable by isomerizing linseed oil by an alkali process, a nickel process, a sulphite process, an iodine compound process, and oxidation process or a tent-butyl hypochlorite process to form the required conjugated double bonds, and has an iodine value from 140 to 170. The content of conjugated double bonds is generally in a range of 10 isomerized linseed oil as defined above is commercially available from the Nisshin Oil Mills, Ltd., under the designationof Nisshin NC-101. In a broad sense, the isomerized linseed oil useful in the present invention includes diesters of ethylene glycol or propylene glycol and linolenic acid and/or linoleic acid which is one component of fatty acids of the isomerized linseed oil and monoesters of monohydric alcohols and the above- mentioned acids.

[0013] The dehydrated castor oil means a triglyceride of fatty acids chiefly composed of conjugated and non-conjugated linoleic acid which are obtained by dehydrating castor oil in the presence or absence of a catalyst, and has an iodine value of 140 or more. In general, the content of the conjugated double bonds is in a range of 20 - 50 %. The dehydrated castor oil as defined above is commercially available under the designations of "Hy-diene" (Soken Chem. Co., Ltd.) and "D.C.O." (Ito Oil Mfg. Co., and Nikka Fat and Oil Co., Ltd.).

[0014] The dehydrated castor oil usable in the process of the invention further includes esters of conjugated linoleic acid which is one component of fatty acids of the dehydrated castor oil or a mixture thereof with non-conjugated linoleic acid, and of mono- or di-hydric alcohols.

[0015] The tall oil means fatty acids of tall oil, glycerides of tall oil and rosins of tall oil. These substances greatly vary in properties depending on their processing history but have generally an iodine value of more than 150 and a content of conjugated double bonds of less than 15 %.

[0016] Linseed oil, perilla oil, safflower oil, henpseed oil, sardine oil and cuttlefish oil, all of which contain as main components triglycerides of linolenic acid and linoleic acid, have an iodine value of 140 or more but contain substantially no conjugated double bonds. In the practice of the invention, esters of linolenic acid and/or linoleic acid which is a fatty acid component of these oils and mono- or dihydric alcohols are also included within the category of the drying oil.

[0017] Isopropenylphenol and its oligomers used in the practice of the invention are those expressed by the following formula (1) and the general formulae (2) and (3):





In the formulae (2) - (3), n is 0 or an integer which generally lies between 1 and 18, and, in all the formulae, each hydroxyl group may be attached to any of the ortho. meta and para positions.

[0018] Among the above-indicated oligomers, the monomer, dimer and trimer are obtainable as substantially pure compounds but higher oligomers including the tetramer are generally obtained in the form of mixtures. The monomer and the oligomers may be used singly or in combination.

[0019] According to the process of the invention the drying oil (I) is first reacted with isopropenylphenol and/or at least one digomer thereof in the presence of an acidic catalyst and in the presence or absence of at least one phenol (V) to introduce the isopropenylphenol and/or at least one oligomer thereof into the drying oil (I) (this reaction is hereinlater referred to as a first-stage modification).

[0020] The isopropenylphenol and/or at least one oligomer thereof are generally employed in an amount, by weight, of 0.1 - 2 times, preferably 0.3 - 1.5 times, as great as that of the drying oil (I). A larger amount than 2 times that of the drying oil (I) will result in unsatisfactory punching quality of the final laminate. A lesser amount than 0.1 times that of the drying oil (I) cannot give a satisfactory modifying effect. When this unsatisfactorily modified oil is used to prepare a phenolic resin, the drying oil separates from the phenolic resin, rendering the resin composition inhomogenous.

[0021] Various types of acids are usable as the acidic catalyst in the first-stage modification and include, for example, mineral acids such as sulphuric acid, nitric acid, phosphoric acid, hydrochloric acid and boric acid, organic acids such as _B-toluenesulphonic acid and oxalic acid, and cation-exchange resins such as of a sulphonic acid type and a carboxylic acid type, The amount of the catalyst may vary over a wide range depending on the type of acid but is generally in a range of 100 - 5,000 ppm, preferably 300 - 3,000 ppm, of the total amount of the reactants, i.e. isopropenylphenol and/or at least one oligomer thereof, the drying oil (I) and, if present, phenol(s).

[0022] The first'stage modification may be carried out by mixing isopropenylphenol and/or at least one oligomer thereof, the drying oil (I), one or phenols if desired, and the acidic catalyst in the above-defined ranges and treating the mixture at a temperature of 65 - 150°C for a time of 0.5 - 3 hours. A reaction at a lower temperature or for a shorter time than the above defined range may result in insufficient introduction of isopropenylphenol and/or its oligomer(s) into the drying oil (I). On the other hand, a higher reaction temperature or a longer reaction time than the above defined range may be unsuitable since polymerization of the drying oil (I) may be induced.

[0023] The completion of the modification reaction can be readily confirmed by observing a substantial disappearance of the isopropenylphenol component by a suitable means such as a gas chromatography.

[0024] The first-stage modification reaction may be conducted in the absence of solvent but it is preferred to carry it out in the presence of one or more phenols (V) other than the isopropenylphenol and/or its oligomer(s) (hereinlater referred to simply as a phenol or phenols). This is because the phenol (V) dissolves isopropenylphenol and/or its oligomer(s) and thus accelerates the modification reaction. Examples of such phenols (V) include butylphenol, amylphenol, hexylphenol, octylphenol, nonylphenol, dodecylphenol, phenylphenol, styrenated phenol, cumylphenol, bisphenol A, phenol, cresol, xylenol, catechol and resorcin.

[0025] These said

generally used in an amount, by weight, of up to 5 times that of the isopropenylphenol and/or its oligomer(s). Larger amounts than the specified upper limit do not appear to offer any partiular advantages.

[0026] The reaction product obtained by the first-stage modification is generally in the form of a liguid and brown in colour. Especially when the modification is conducted in the presence of the aaid phenol(s) (V) the reaction product is uniformly dissolved in the said phenol(s) (V).

[0027] The reaction product (II) obtained by the first-stage modification is then further reacted with a phenol or phenols (VI) in the presence of an acidic catalyst to introduce the phenol or phenols (VI)into the first phenolic modified dryihg oil (II). If the reaction product (II) of the first-stage modification contains the said phenol(s) (V) such may be removed from the reaction product (II) prior to the second-stage modification reaction, if necessary, or the reaction product (II) containing the phenol(s) (V) may be used as it is without removal of the said phenol(s) (V). Further, it is unnecessary to remove or neutralize the acidic catalyst employed for the first-stage modification reaction.

[0028] The phenol(s) (VI) employable in the second-stage modification reaction are those which are particularly indicated for the first-stage modification. If one or more phenols (V) is/are used in the first- stage modification, such may be the some or different todifferent to the phenol(s) (VI) used in the second-stage modification.

[0029] The amount of the phenol(s) (VI) used in the second-stage modification reaction varies in relation to the amount of the phenol(s) (V) employed in the first-stage modification reaction, if any. The total amount of the phenol(s) (V) + (VI) employed in the first-stage and the second -stage modifications is generally in a range, by weight, of 0.1 - 5 times, preferably 0.5 to 2 times, that of the drying oil (I). A lesser amount than 0.1 times that of the drying oil (I) results in a final laminate which is unsatisfactory with regard to mechanical strength, resistance to moisture and its waterproofing properties. A larger amount than 5 times that of the drying oil (I) cannot improve sufficiently the punching quality of a final laminate.

[0030] The reaction product (II) obtained by the first-stage modification contains an acidic catalyst employed in the first stage. However, such residual catalyst is generally insufficient in amount to permit the second-stage modification reaction to proceed. Accordingly, it is generally necessary to add a further amount of acidic catalyst in order to effect the second-stage modification reaction. The acidic catalyst suitable for the second-stage modification is, for instance, a strong acid such as p-toluenesulpnonie acid, sulphuric acid, hydrochloric acid, or the like acid. The amount of the acid may be in a range of 500 - 10,000 ppm, preferably 1,000 - 5,000 ppm, of the total amount of the reactants, i.e., the reaction product (II) of the first-stage modification and the said phenol(s) (VI) added for the second-stage modification reaction. A larger amount than 10,000 ppm tends to induce polymerization of the drying oil while a lesser amount than 500 ppm hardly assists in expediting the modification reaction. The reaction temperature and time in the second-stage are preferably in ranges of 80 - 140°C and 0.5 - 3 hours, respectively. These reaction conditions are generally much milder than known modification conditions where drying oils are modified with phenols, i.e., at temperatures of 80 - 180°C and for 1 - 6 hours.

[0031] The completion of the second-stage modification reaction can be confirmed by checking the amount of consumed phenol or phenols by a suitable means such as a gas chromatography.

[0032] The termination of the reaction can be carried out by neutralization using an alkali such as ammonia.

[0033] As a result, there is obtained a reaction product (III) in the se=cond-stage modification which is normally in the form of a liquid and brown in colour.

[0034] The reaction products (II) and (III) obtained in the first-stage and the second-stage modification reactions will be particularly described with regard to their structures.

[0035] In the first-stage modification, when, for example, a methyl ester of 9, 11-octadecadienoic acid is reacted with p-isopropenylphenol and/or its oligaer(s) in the presence of 1,000 ppm of a sulphuric acid catalyst at 100°C for 1 hour, the resulting product has been found by a gas chromatography and a mass spectrum analysis to have such a structure in which two molecules of p-isopropenylphenol or one molecule of p-isopropenylphenol dimer has/have added to or has/have combined with one molecule of methyl 9,11-octadecadienoic acid ester. Further, infrared absorption spectrum and nuclear magnetic resonance spectrum analyses reveal that the conjugated diene of 9,11-octadecadienoic acid remains as it is. Thus, it is believed that the reaction product obtained by the first-stage modification of dehydrated castor oil has, for example, the following chemical structure:

(wherein R₁ represents a glyceride residue, and either R₂ and R₃ independently represent the

radical, or R₂ represents a hydrogen atom and R₃ represents

[0036] Then, the second-stage modification is conducted by reacting the reaction product with cresol in the presence of sulphuric acid in an amount of 2,000 ppm of the reaction mixture including cresol at 100°C for 1 hour. The resulting reaction product, where two molecules of cresol are introduced into the product, is assumed to have the following structural formula as determined by infrared absorption spectrum and nuclear magnetic resonance specturm analyses:

(wherein R₁ R₂ and R₃ have the same meanings as defined above and R₄ represents the

[0037] It will be seen from the above that when isopropenylphenol and/or its oligomer(s) is/are reacted with the drying oil (I) in the first-stage modification, the unsaturated double bonds of the drying oil (I) remain as they are in the molecule of the reaction product (II). This can never be observed when drying oils are modified with phenols by known techniques. The retention of the unsaturated double bonds which occurs only when the modification is conducted by use of isopropenylphenol and/or its oligomer(s) is one of the important features of the process of the invention. When, for example, dehydrated castor oil is modified with phenols by known techniques, the resulting product is that obtained by the Friedel-Crafts reaction, as described in Japanese Patent Publication No. 45-35918. The product in which two molecules of a phenol are introduced into the drying oil can be expressed, for example, by the following general formula

(wherein R₁ has the same meaning as defined hereinbefore and each R₅ represents the

(wherein R represents a group such as an alkyl group)).

[0038] In practice, the reaction product (III) obtained in the second-stage modification constitutes a phenolic component and such is reacted with formaldehyde or a compound based of formaldehyde (which will be defined hereinlater and referred herein to simply as formaldehyde) to produce a modified phenolic resin (IV).

[0039] The production of the phenolic resin is feasible by various methods including: a method in which the phenolic component and formaldhyde are reacted under acidic conditions to give a novolac type resin; a method in which the reactants are partly reacted under acidic conditions, followed by rendering the reaction system alkaline for undergoing subsequent reaction to obtain a novalac-resol type resin, and a method in which the reaction product obtained after the modification reactions is rendered basic and reacted with formaldehyde to obtain a resol type resin. In order to obtain a resol type resin, the acidic catalyst which remains in the reaction product of the second-stage modification may first be neutralized with ammonia, organic amines, etc., and then subjected to reaction with formaldehyde.

[0040] Whichever method is used for the production of phenolic resin, the reaction product (III) after the second-stage modification may first be treated with a phenol or phenols is required before reaction with formaldehyde. Such phenol(s) may be chosen from those indicated above for the first-stage and second-stage modification reactors. The phenol(s) which may be added in this stage and those employed for the first-stage and second-stage modifications may be the same or different.

[0041] The ratio of any added phenol(s) to the reaction product (III) after the second-stage modification may be determined such that the drying oil (I) is contained in a range of 10 - 100 %, preferably 20 - 60

the total amount of the phenolic constituents (i.e., the total amount of the added phenol(s), and isopronenvl- phenol and/or its oligomer(s) and the phenol(s) employed in the first-stage and the second-stage modification reactions, respectively). A lesser amount of the drying oil than 10 wt % may result in a final laminate which is unsatisfactory in flexibility and not improved in punching quality to a satisfactory extent. On the other hand, a larger amount than 100 wt % is not preferable since a laminate using such phenolic resin may show poor mechanical strength.

[0042] An amount of drying oil (I) ranging from 20 - 60 wt 96 is especially suitable for producing a phenolic resin (IV) to result in a final laminate which shows excellent punching quality, resistance to moisture and waterproofness.

[0043] The term "formaldehyde or compound based on formaldehyde" includes an aqueous solution of formaldehyde, paraformaldehyde as well as formaldehyde per se. The amount of the formaldehyde used is generally in a range of 0.7 - 2.0 moles, preferably 0.8 - 1.6 moles, per mole of the total phenolic constituents. Outside the broader range, when the resulting phenolic resin is applied for making a laminated sheet, high density of crosslinkage may not be attainable and the laminate may become unsatisfactory with regard to mechanical strengths, resistance to moisture and waterproofness.

[0044] The reaction of the phenolic component (III) and formaldehyde is normally conducted in the presence of a catalyst. where a novelac type resin is prapared hydrochloric acid, oxalic acid, p-toluner-sulphonic a sulphuric acid and the like acids may be employed asthe catalyst. On the other hand, where a resol type resin is prepared, there may be used as catalyst ammonia, methylamine, dimethylamine, triethylamine, ethylene diamine, diethylamine, sodium hydroxide, potassium hydroxide and the like. As a matter of course, a novolac-resol type resin is obtainable by interacting the phenolic component (III) and formaldehyde to an extent in the presence of the above-indicated acid, and adding a base to the reaction system to effect a further reaction under basic conditions.

[0045] The amount of catalyst required varies considerably depending on the kind of the catalyst but is normally in a range of 0.1 - 2 wt % of total reactants in the case of the acid and in a range of 0.05 - 5 wt % in the case of the base. Especially when a mixture of ethylene diamine, ammonia and/or an organic amine which contains 10 - 20 mole % of ethylenediamine is used, the resulting modified phenolic resin (IV) can yield a laminate showing excellent properties.

[0046] The reaction temperature and time vary depending on the kind(s) of phenol(s), if any, in the phenolic component (VII), the kind and amount of acid or base, and other reaction parameters, but is generally in ranges oi du - 110°cand 1 - 5hours, respectively.

[0047] By measuring a time required for the gelation of the reaction mixture at 150°C, it has been shown that the polyaddition and polycondensation of the phenolic component (VII) and formaldehyde has proceeded to a desired extent, thus determining the end of the reaction. After completion of the reaction, the reaction system may subsequently be treated to remove water from the system to obtain a modified phenolic resin (IV). The thus obtained modified phenolic resin (IV) can be dissolved in various kinds of solvents to give varnishes. Examples of such solvents are aromatic hydrocarbons such as benzene, toluene, xylene, etc., ketones such as acetone, methyl ethyl ketone, etc., alcohols such as methanol, ethanol, etc., and mixtures thereof. The resin varnish may be impregnated into a suitable substrate such as of paper, glass cloth, etc., and dried to give a prepreg. These prepregs may be superposed one on another and pressed under heating conditions to obain a laminate.

[0048] The process of the present invention has a number of advantages which will be understood from the following description.

[0049] Drying oils having an iodine value of more than 140 and a content of conjugated double bonds of less than 50% are generally weak in reactivity with phenols, so that it is difficult to apply the oils for preparation of modified phenolic resins. Applicable drying oils have been limited only to those which have high content of conjugated double bonds, e.g. tung oil.

[0050] According to the process of the invention, nowever, drying oils which are low in content of conjugated double bonds are efficiently modified with ise- propenylphenol and/or its oligomer(s) and phenol(s). These phenol-introduced oils are effectively usable for preparing modified phenolic resins. In other words, drying oils of the specific type which have been considered diffuclt to use in the preparation of modified phenolic resins can be effectively utilized for preparing modified phenolic resins according to the process of the invention.

[0051] The present invention has another advantage in that it is possible to introduce isopropenylphenol and/or its oligomer(s) into drying oils under relatively mild conditions in the first-stage modification. In the reaction product (II) obtained in the first-stage modification, the double bonds of the oils remain as they are without disappearance as shown, for example, in the foregoing formula (4). This has never been experienced in the case where drying oils are modified with phenols according to known methods, and is believed to be based on the specific reactivity of isopropenylphenol used in the present invention.

[0052] Since the double bonds of drying oils remain, as they are in the reaction product (II) of the first-stage modification, hydroxyphenyl radicals can be further introduced into the oils in the second-stage modification using phenol(s) (VI). The modification treatments of drying oils consisting of the two stages ensure introduction of hydroxylphenyl radicals in much greater amount per molecule of the drying oil than in the case of known methods. In addition, polymerization of drying oils can be suppressed by conducting the modifications in two stages.

[0053] Accordingly, a further advantage of the invention is that when used as phenolic component or part thereof for reaction with formaldehyde or a compound based thereon, the reaction product (III) obtained in the second-stage modification readily reacts with formaldenyde or a compound based thereon and thus methylol radicals can be introduced at a high rate. The resulting phenolic resin (IV) can be easily dissolved in a solvent to give a uniform and stable varnish. The varnish is ready to permeate into substrates, ensuring uniform impregnation.

[0054] When treating the resulting prepregs under heating and pressurizing conditions for lamination, it has been found that the phenolic resin of this type increases in crosslinking density and the laminate obtained is improved in interlaminar strength. The laminate using the modified phenolic resin (IV) obtained according to the process of the invention is not only flexible and excellent with regard to punching quality, but also shows excellent electrical characteristics, resistance moisture, waterproofness, chemical resistance and mechanical strength.

[0055] The present invention will be described by the following examples which percentage is by weight unless otherwise indicated. Comparative examples follow the examples of the invention.

Example 1.

[0056] 270 g of a mixture of p-isoprophenylphenol and its oligomers having a composition of 3% of p-isopropenylphenol, 87 % of its dimer and 10 % of a trimer and higner oligomers and 395 g of isomerized linseed oil were maintained at 140°C under agitation. 1.7 g of 85 % phosphoric acid was charged into the mixture, followed by agitation. 1.7 g of 85 % phosphoric acid was charged into the mixture, followed by agitating for 2 hours. After completion of the reaction, the reaction mixture was cooled, to which were added 193 g of synthetic cresol (consisting of 60 % of the m-isomer and 40 % of the p-isomer) and 5.5 g of 20 % sulphuric acid for further reaction at 100°C for 1 hour.

[0057] Thereafter, 430 g of phenol, 210 g of octylphenol, 210 g of nonylphenol, 1010 g of 37 % aqueous solution of formaldehyde, 32 g a4.5 % aqueous ammonia and 3.1 g of ethylenediamine were added to the reaction system

for 5 hours. Then, water was removed under reduced pressure. After cooling, the resulting resin was dissolved in a mixed solvent consisting of methanol and toluene in a mixing ratio of 2 : 1 to obtain a varnish having a resin concentration of 50 %.

[0058] The thus obtained resin varnish was impregnated in sheets of 10 mils thick linter paper and dried to obtain prepregs each having a resin content of 45 %. Nine prepregs were superposed and laminated under a pressure of 90 kg/cm², at 160°C for 50 minutes to obtain a laminate.

[0059] Further, the above lamination procedure was repeated using a 35 µ thick copper foil to obtain a copper-clad laminate. The both laminates had a thickness of 1.6 mm.

Example 2.

[0060] 270 g of a mixture of p-isopropsylphenol and its oligomers having a composition of 20 % of p-isopropenylphenol, 69 % of the dimer, and 11 % of the trimer and higher oligomers thereof, 210 g of nonylphenol and 395 g of isomerized linseed oil were maintained at 140°C under agitation, to which was added 1.95 g of 40 % p-toluenesulphonic acid. The mixture was agitated for 2 hours for reaction. After completion of the reaction, the reaction mixture was cooled, to which were further added 190 g of synthetic cresol (consisting of 60 % of the m-isomer and 40 % of the p-isomer) and 4.0 g of 20 % sulphuric acid for reaction at 100°C for 1 hour.

[0061] To the reaction system were further added 430 g of phenol, 210 g of octylphenol, 1010 g of 37 % aqueous solution of formaldehyde, 32 g of 24.5 % of aqueous ammonia, and 3.1 g of ethylenediamine for reaction at 98 - 100°C for 4 hours. Then, water was removed under reduced pressure and the resulting reaction product was cooled and dissolved in a mixed solvent consisting of methanol and toluene in a mixing ratio of 2:1 to obtain a varnish having a resin concentration of 50 %. Then, the procedure of Example 1 was repeated to give a laminate and a copper-clad laminate each1.6mm in thickness.

Example 3.

[0062] 200 g of a mixture of p-isopropenylphenol and its oligomers having a composition of 10 % of p-isopropenylphenol, 75 % of its dimer and 15 % of trimer and higher oligomers, 177 g of phenol and 300 g of isomerized linseed oil were maintained at 85°C under agitation, to which was added 3.7 g of 20 % sulphuric acid. The reaction system was agitated for 2 hours for reaction. After completion of the reaction, the system was cooled and added with 150 g of synthetic cresol (consisting of 60 % of the m-isomer and 40 % of the p-isomer) and 3. 8 g of 20 % sulphuric acid for reaction at 100°C for 1 hour.

[0063] To the reaction system were further added 200 g of phenol, 289.6 g of nonylphenol, 845 g of 37 % aqueous solution of formaldehyde, 30 g of 24.5 % aqueous ammonia, and 2.6 g of ethylenediamine for reaction at 98 - 100°C for 4 hours. Water was removed from the reaction system under reduced pressure and the product was cooled and dissolved in a mixed solvent consisting of methanol and toluene in a mixing ratio of 2 : 1 to obtain a varnish having a resin concentration of 50 %.

[0064] Then, the procedure of Example 1 was repeated to obtain a laminate and a copper-clad laminate each 1.6 mm in thickness.

Example 4.

[0065] 340 g of a mixture of p-isopropenylphenol and its oligomers having a composition of 95 % of p-isopropenylphenol, 3 % of dimer, and 2 % of trimer and higher oligomers and 500 g of dehydrated castor oil were maintained at 140°C under agitation, to which was further added 2.2 g of 85 % phosphoric acid, followed by agitating for 2 hours for reaction. After completion of the reaction, the reaction system was cooled, to which were further added 244 g of synthetic cresol (consisting of 60 % of the m-isomer and 40 % of the p-isomer) and 7.0 g of 20 % sulphuric acid for reacticn at 100°C for 1 hour. To the reaction system were then added 544 g of phenol, 266 g of octylphenol, 266 g of nonylphenol, 1278 g of 37 % aqueous solution of formaldehyde, 41 g of 24.5 % aqueous ammonia and 3. 9 g of ethylenediamine for reaction at 98 - 100°C for 5 hours. Then, water was removed from the reaction system under reduced pressure and the resulting product was cooled and dissolved in a mixed solvent consisting of methanol and toluene in a mixing ratio of 2:1 to obtain a varnish having a resin concentration of 50%.

[0066] Then, the procedure of Example 1 was repeated to give a laminate and a copper-clad laminate each 1.6 mm in thickness.

Example 5

[0067] 340 g of a mixture of p-isoprophenylphenol and oligomers thereof having a composition of 3% of p-isopropenylphenol, 87% of dimer, and 10% of trimer and higher oligomers and 500 g of dehydrated castor oil were maintained at 140°C under agitation, into which was charged 2.2 g of 85% phosphoric acid. The reaction system was agitated for 2 hours for reaction. After completion of the reaction, the system was cooled and treated with 127 g of phenol, 127 g of resorcine and 7.2 g of 20% sulphuric acid for reaction at 100°C for 1 hour.

[0068] To the reaction system were thereafter added 520 g of phenol, 253 g of octylphenol, 260 g of nonylphenol, 1278 g of 37% aqueous solution of formaldehyde, 40.5 g of 24.5% aqueous ammonia and 4.30 g of ethylenediamine for reaction at 98 - 100°C for 4 hours. Then water was removed from the system under reduced pressure and the resulting product was cooled and dissolved in a mixed solvent of methanol and toluene in a mixing ratio of 2 : 1 to obtain a varnish having a resin concentration of 50 %.

[0069] Then, the procedure of Example 1 was repeated to obtain a laminate and a copper-clad laminate each 1.6 mm in thickness.

Example 6.

[0070] 350 g of a mixture of p-isopropenylphenol and its oligomers having a composition of 98 % of p-isopropenylphenol and 2 % of dimer and trimer thereof and 510 g of linseed oil were maintained at 120°C under agitation, into which was charged 2.2 g of 40 % sulphuric acid, followed by agitating for 2 hours for reaction. After completion of the reaction, 244 g of synthetic cresol (consisting of 60 % of the m-isomer and 40 % of the p-isomer) and 3. 5 g of 40 % sulphuric acid were added to the reaction system for further reaction at 100°C for 1.5 hours.

[0071] To the system were further added 550 g of phenol, 530 g of nonylphenol, 1280 g of 37 % aqueous solution of formaldehyde, 41 g of 24.5 % aqueous ammonia and 4.0 g of 24.5 % aqueous ammonia and 4.0 g of ethyleneiiamine for reaction at 98 - 100°C for 5 hours. Then water was removed from the system under reduced pressure and the resulting product was cooled and dissolvei in a mixted solvent consisting of methanol and toluene in a mixing ratio of 2 : 1 to obtain a varnish having a resin concentration of 50 %.

[0072] Thereafter, the procedure of Example 1 was repeated to obtain a laminate and a copper-clad laminate each 1.6 mm in thickness.

Example 7.

[0073] 350 g of p-isopropenylphenol having a composition of 98 % of p-isopropenylphenol and 2 % of dimer and trimer thereof, 300 g of phenol and 600 g of linseed oil were maintained at 85°C under agitation, into which was charged 3.1 g of 40 % sulphuric acid, followed by agitating for 2.5 hours for reaction. After completion of the reaction, 230 g of synthetic cresol and 2.8 g of 40 % sulphuric acid were added to the system for further reaction at 100°C for 1.5 hours.

[0074] To the reaction system were further added 350 g of phenol, 480 g of nonylphenol, 1400 g of 37 % aqueous solution of formaldehyde, 50 g of 24.5 % aqueous ammonia and 4.3 g of ethylenediamine for reaction at 98 - 100°C for 4 hours. Then water was removed from the system under_leduced pressure and, after cooling, the resulting product was dissolved in a mixed solvent of methanol and toluene in a mixing ratio of 2 : 1 to obtain a varnish having a resin concentration of 50 %.

[0075] Then, the procedure of Example 1 was repeated to obtain a laminate and a copper-clad laminate each 1.6 m in thickness.

Example 8.

[0076] 350 g of p-isopronylphenol oligomers having a composition of 90 % of p-isoropenylphenol dimer and 10 % of trimer and higher oligomers, 270 g of nonylphenol, and 500 g of linseed oil were maintained at 140°C under agitation, into which was charged 2.5 g of 85 % phosphoric acid, followed by agitating for 2 hours for reaction. After completion of the reaction, the reaction system was cooled, to which were added 250 g of synthetic cresol and 2.3 g of 40 % sulphuric acid for further reaction at 100°C for 1 hour.

[0077] To the reaction system were further added 540 g of phenol, 250 g of octylphenol, 1300 g of 37 % aqueous solution of formaldehyde, 40.5 g of 24.5 % aqueous ammonia and 4.0 g of ethylenediamine for reaction at 98 - 100°C for 4 hours. When water was removed from the system under reduced pressure and, after cooling, the resulting product was dissolved in a mixed solvent of methanol and toluene in a mixing ratio of 2 : 1 to obtain a varnish having a resin concentration of 50 %.

[0078] Then, the procedure of Example 1 was repeated to obtain a laminate and a copper-clad laminate each 1.6 mm in thickness.

Example 9.

[0079] 340 g of oligomers of p-isobropenylphenol having a composition of 90% of p-isopropanylphenol dimer and 10 % of trimer and higher oligomers and 500 g of cuttlefish oil were maintained at 100°C under agitation, into which was charged 2.2 g of 85 % phosphoric acid. The reaction system was agitated for 2 hours for reaction. After completion of the reaction, 200 g of synthetic cresol, 80 g of xylenol and 3.8 g of 40 % sulphuric acid were added to the system for further reaction at 100°C for 1 hour. To the system were further added 540 g of phenol, 260 g of octylphenol, 270 g of nonylphenol, 1300 g of 37 % aqueous solution of formaldehyde, 41 g of 24.5 % aqueous ammonia and 4.0 g of ethylenediamine for reaction at 98 - 100°C for 4 hours. Then water was removed from the system under ieduced pressure and, after cooling, the resulting product was dissolved in a mixed solvent of methanol and toluene in a mixing ratio of 2 : 1 to obtain a varnish having a resin concentration of 50 %.

[0080] Then, the procedure of Example 1 was repeated to obtain a laminate and a copper-clad laminate each 1.6 mm in thickness.

Example 10.

[0081] 350 g of p-isopropenylphenol having a composition of 98 % of p-isopropenylphenol and 2 % of dimer and timer thereof, 266 g of nonylphenol and 650 g of glyceride of tall oil were maintained at 100°C under agitation, into which 5.5 g of 20 % sulphuric acid was charged, followed by agitating for 2 hours for reaction. After completion of the reaction, 240 g of synthetic cresol and 5.1 g of 20 % sulphuric acid were further added to the reaction system for further reaction at 100°C for 1.3 hours. To the system were further added 560 g of phenol, 270 g of octylphenol, 1280 g of 37% aqueous solution of formaldehyde, 41 g of 24.5 % aqueous ammonia and 3.9 g of ethylenediamine for reaction at 98 - 100°C for 3.5 hours. Then water was removed from the system under reduced pressure and, after cooling, the resulting product was dissolved in a mixed solvent of methanol and toluene in a mixing ratio of 2 : 1 to obtain a varnish having a resin concentration of 50 %.

[0082] Then, the procedure of Example 1 was repeated to obtain a laminate and a copper-clad laminate each 1.6 mm in thickness.

Example 11.

[0083] 340 g of oligomers of p-isopropenylphenol having a composition of 90 % of p-isopropenylphenol dimer and 10 % of trimer and higher oligomers and 500 g of glyceride of tall oil were maintained at 100°C under agitation, into which was charged 2.2 g of 85% phosphoric acid, followed by agitating for 2 hours for reaction. After completion of the reaction, the reaction system was cooled and added with 200 g of synthetic cresol, 80 g of xylenol and 3.8 g of 40% sulphuric acid for reaction at 100°C for 1 hour. To the system were further added 540 g of phenol, 260 g of octylphenol, 270 g of nonylphenol, 1300 g of 37 % aqueous solution of formaldehyde, 41 g of 24.5% aqueous ammonia and 4.0 g of ethylenediamine for reaction at 98 - 100°C for 4 hours. Then water was removed from the system under reduced pressure and, after cooling, the resulting product was dissolved in a mixed solvent of methanol and toluene in a mixing ratio of 2 : 1 to obtain a varnish having a resin concentration of 50 %.

[0084] Then, the procedure of Example 1 was repreated to obtain a laminate and a copper-clad laminate each 1.6 mm in thickness.

Example 12.

[0085] 340 g of oligomers of p-isopropenylphenol having a composition of 90% of p-isopropenylphenol dimer and 10 % of trimer and higher oligomers and 500 g of tall oil were maintained at 140°C under agitation, into which was charged 2.2 g of 85 % phosphoric acid. The mixture was agitated for 2 hours for reaction. After completion of the reaction, the reaction system was cooled, to which were further added 130 g of phenol, 130 g of resorcine and 3.6 g of 40% sulphuric acid for further reaction at 100°C for 2 hours.

[0086] To the reaction system were then added 500 g of phenol, 250 g of octylphenol, 280 g of nonylphenol, 1278 g of 37% aqueous solution of formaldehyde, 41 g of 24.5 % aqueous ammonia and 4.3 g of ethylenediamine for reaction at 98 - 100°C for 4 hours. Then water was removed from the system under reduced pressure and, after cooling, the resulti.ng product was dissolved in a mixed solvent of methanol and toluene in a mixing ratio of 2 : 1 to obtain a varnish having a resin concentration of 50 %.

[0087] Thereafter, the procedure of Example 1 was repeated to obtain a laminate and a copper-clad laminate each 1.6 mm in thickness.

Comparative Example 1.

[0088] 423 g of cresol, 210 g of isomerized linseed oil and 13.65 g of 20 % sulphuric acid were mixed for reaction at 120°C for 3 hours. After completion of the reaction, the reaction system was cooled, to which were added 551 g of 37 % aqueous solution of formaldehyde, 139 g of nonylphenol, 139 g of octylphenol, 20 g of 24.5 % aqueous ammonia and 1.6 g of ethylenediamine for reaction at 97 - 98°C for 2.5 hours. Then water was removed from the system under reduced pressure and, after cooling, the resulting product was dissolved in a mixed solvent of methanol and toluene in a mixing ratio of 2 : 1 to obtain a varnish having a resin concentration of 50 %.

[0089] Then, the procedure of Example 1 was repeated to obtain a laminate and a copper-clad laminate each 1.6 mm in thickness.

Comparative Example 2.

[0090] 604 g of cresol, 300 g of dehydrated castor oil and 19.5 g of 20 % sulphuric act- were mixed for reaction art 120°C for 3 hours. After completion of the reaction, the reaction system was cooled, to which were added 757 g of 37 % aqueous solution of formaldehyde, 200 g of nonylphenol, 200 g of octylphenol, 26.6 g of 24.5 % aqueous ammonia and 2.3 g of ethylenediamine for further reaction at 97 - 98°C for 2.5 hours. Then water was removed from the system under reduced pressure and, after cooling, the resulting product was dissolved in a mixed solvent of methanol and toluene in a mixing ratio of 2 : 1 to obtain a varnish having a concentration of 50 %.

[0091] Then, the procedure of Example 1 was repeated to obtain a laminate and a copper-clad laminate each 1.6 mm in thickness.

Comprarative Example3.

[0092] 600 g of cresol, 350 g of linseed oil and 14.3 g of 40 % sulphuric acid were mixed for reaction at 120°C for 3 hours. After completion of the reaction, the reqction system was cooled, to which were added 760 g of 3796 aqueous solution of formaldehyde, 200 g of nonylphenol, 200 g of octylphenol, 29.0 g of 24.5% aqueous ammonia and 2.5 g of ethylenediamine for reaction at 98 - 100°C for 2.5 hours. Then water was removed from the system under reduced pressure and, after cooling, the resulting product was dissolved in a mixed solvent of methanol arm toluene in a mixing ratio of 2 : 1 to obtain a varnish having a resin concentration of 50 %.

[0093] Then, the procedure of Example 1 was repeated to obtain a laminate and a copper-clad laminate each 1.6 mm in thickness.

Comparative Example 4

[0094] 300 g of p-iusopropenylphenol oligomers having a composition of 90% of p-isopropenylphenol dimer and 10% of trimer and higher oligomers, 264 g of phenol and 450 g of linseed oil were maintained at 85°C under agitation, into which was charged 2.9 g of 40% sulphuric acid, followed by agitating for 2 hours. To the reaction system were further added 380 g of synthetic cresol, 110 g of nonylphenol, 110 g of octylphenol, 630 g of 37% aqueous solution of formaldehyde, 23.0 g of 24.5% aqueous ammonia and 2.0 g of ethylenediamine for reaction at 97 - 98°C for 2.5 hours. Then water was removed from the reaction system under reduced pressure. Upon gelation, the phenolic resin and linseed oil separated from each other and thus the resulting modified phenolic resin was imhomogeneous. The resin could not be used far making a laminate.

Comparative Example 5

[0095] 600 g of cresol, 350 g of glyceride of tall oil and 14.3 g of 40 sulphuric acid were mixed forreaction at 120°C for 3 hours. After completion of the reaction, 760 g of 37% aqueous solution of formaldehyde, 200 g of nonylphenol, 200 g of octylphenol, 29.0 g of 24.5% aqueous ammonia and 2.5 g of ethylenediamine were added to the reaction system for further reaction at 98 - 100°C for 2.5 hours. Then water was removed from the system under reduced pressure and, after cooling, the resulting product was dissolved in a.mixed solvent of methanol and toluene in a mixing ratio of 2 : 1 to obtain a varnish having a resin concentration of 50 %.

[0096] Then, the procedure of Example 1 was repeated to obtain a laminate and a copper-clad laminate each 1.6 mm in thickness.

[0097] The laminates obtained in the foregoing Examples and Comparative Examples were tested to determine their characteristic properties with the results of the Table below.

[0098] The test was carried out by the following methods.

(1) Water absorption, insulating resistance, hot solder resistance and resistance to trichloroethylene were determined according to the methods prescribed in JIS (Japanese Industrial Standard) C 6481.

(2) Punching quality was determined according to the method prescribed in ASTM D-614-44.

(3) Dimensional variation was determined by a method wherein a test piece having a size of 140 mm in length and 13 mm in width was heated at 100°C for 24 hours and then cooled down to room temperature.

(4) Warp was determined by a method wherein a test piece having a size of 140 mm x 13 mm was heated at 100°C for 24 hours and then cooled down to room temperature.

[0099] A straight ruler was laid on the concave parts of the laminate and the greatest clearance was measured as the warp of the sample.

Claims

1. A process for producing a modified phenolic resin by reacting a phenolic component and formaldehyde or a compound based on formaldehyde, the phenolic component consisting, at least in part, of a phenolic modified drying oil, characterised in that the drying oil (I) used is a drying oil having an iodine value of 140 or more and a content of conjugated double bonds of less then 50 % and the drying oil (I) is reacted with isopropenylphenol and/or at least one oligomer thereof in the presence of an acidic catalyst and in the presence or absence of at least one phenol (V) to form a first phenolic modified drying oil (II), that the modified drying oil (II). is further reacted with at least one phenol (VI) in the presence of an acidic catalyst to form a further phenolic modified drying oil (III) and that the further modified drying oil (III) is used as or as part of a phenolic component (VII) which is reacted with formaldehyde or a compound based on formaldehyde to product a modified phenolic resin (IV).

2. A process according to Claim 1, wherein the phenol constituent(s) (V) is/are chosen from butylphenol, anylphenol, hexylphenol, octylphenol, nonylphenol, dodicylphenol, phenylphenol, styrenated phenol, cumylphenol, bisphenol A, phenol, cresol, xylenol, catechol and resorcin.

3. A process according to Claim 1 or Claim 2, wherein the phenolic component (VII) contains the further modified drying oil and at least on phenol chosen from butylphenol, amylphenol, hexylphenol, octylphenol, nonylphenol, dodecylphenol, phenylphenol, styrenated phenol, c.unylphenol, bisphenol A, phenol, cresol, xylenol, catechol and resorcin.

4. A process according to any preceding claim, wherein the drying oil (I) is chosen from isomerized linseed oil, dehydrated castor oil and tall oil.

5. A process according to any one of Claims 1 to 3, wherein the drying oil (I) is chosen fromlinseed oil perilla oil, safflower oil, hempseed oil, sardine oil and cuttlefish oil.

6. A process according to any preceding claim, wherein the further modified drying oil (III) is reacted with aqueous formaldehyde to produce a modified phenolic resin (IV).

7. A process according to any preceding claim, wherein the amount of isopropenylphenol and/or at least one oligomer reacted with the drying oil (I) to form the modified drying oil (II) is 0.1 - 2 times as great as that of the drying oil (I).

8. A process according to any preceding claim, wherein the reaction to form the modified drying oil (II) is conducted at a temperature of 65 - 150°C for 0.5 - 3 hours.

9. A process according to any preceding claim, wherein the drying oil (I) is reacted with a mixture of p-isopropenylphenol and oligomers thereof to form the first phenolic modified drying oil (II).

10. A process according to any preceding claim, wherein the acidic catalyst for forming the first modified drying oil and/or the further modified drying oil is chosen from phosphoric acid, p-toluene sulphonic acid and sulphnric acid.