an object of the invention is to produce a novolac alkylphenol resin having a residual rate of alkylphenol ( s ) of less than 2 %, preferably less than or equal to 1 . 5 %, and most preferably less than or equal to 1 % while having a softening point temperature between 85 and 105 ° c ., preferably between 95 and 105 ° c . the resins may be obtained using one or several alkylphenolic monomers , one or several aldehydes , and 2 to 20 %, more preferably 5 to 10 %, by weight based on the alkylphenol ( s ), of at least one saturated or unsaturated fatty acid . the alkylphenols are phenols , preferably alkylated with a hydrocarbonated alkyl group in para position of the phenol group and having 6 to 10 carbon atoms . the use of a tertioctyl alkyl group , such as para - tertiary octylphenol , is the most preferred . in addition to the alkylphenolic monomers described above , the novolac resins can also contain other phenols . these other phenols can represent up to 30 % of the total mass of the phenols of the resin . suitable other phenols include phenol , resorcinol , cardanol , and dialkylphenols , such as dimethylphenols , xylenols , or 2 , 4 or 2 , 6 - ditertiary octylphenols . the fatty acids may be saturated mono - carboxylic acids or mono - olefinics having at least 8 carbon atoms . preferably , the saturated fatty acids have 8 to 32 carbon atoms . suitable saturated fatty acids include caprylic , pelargonic , capric , undecylic , lauric , stearic and behenic acid . suitable unsaturated fatty acids include oleic and undecylic acids . it is also possible to use synthetic or natural mixtures of these fatty acids , which can be obtained by saponification of vegetable oils or animal fats . stearic acid is especially preferred . another object of the invention relates to a process for preparing a novolac alkylphenol resins . for the resins that contain formol , the formol is usually introduced into the reaction medium in the form of an aqueous solution ; it can also be introduced in the form of paraformaldehyde . the novolac resin can be prepared by synthesizing formophenolic resins of the novolac type with aldehydes / alkylphenol having a molar ratio greater than 0 . 9 . a first resin with elevated softening point temperature ( i . e . greater than 110 ° c .) is formed . the fatty acid or acids are then added while the resin is again in a melted state . the resin may be melted , either in the synthesis reactor or in the presence of the fatty acid or acids , which are agitated in order to mix it / them with in the resin in a homogeneous manner . alternatively , the condensation of the aldehydes or aldehydes may be carried out with the alkylphenol ( s ) in the presence of the fatty acid ( s ) at temperatures less than or equal to 200 ° c ., preferably less than or equal to 180 ° c ., most preferably less than or equal to 160 ° c . the preparation of the resin in a single step offers several advantages in comparison to the procedure described above , where the alkylphenol ( s ) and aldehydes ( s ) are condensed before being mixed with the fatty acid ( s ). first , the formation of a reaction medium with elevated viscosity in the reactor at the time of synthesis of the novolac resin is avoided or reduced . second , the use of elevated temperature that is otherwise required or desirable in conventional techniques can also be avoided . the preferred procedure described above can either be a procedure of the batch type or a continuous procedure in which alkylphenol ( s ), fatty acid ( s ) and aldehydes ( s ) are introduced continuously into the reactor or into a series of reactors . a description of continuous procedures can be found in knop et al ., “ chemistry and application of phenolic resins ,” polymer / properties and application , ed . springer - verlag berlin heidelberg , new york , p . 62 - 64 ( 1979 ), herein incorporated by reference in its entirety . in general , the process may be carried out by introducing alkylphenol ( s ) and fatty acid ( s ) into the reactors , followed by the acid catalyst or catalysts into the reactors ; the mixture is then brought to 80 - 100 ° c . at atmospheric pressure and the aldehydes or aldehydes are introduced to flow in over a period that varies from 15 to 100 minutes , the mixture being kept under agitation . when the aldehyde is formol , preferably a solution of formaldehyde in water is used and the medium is held at reflux until the formaldehyde is finished flowing in . after the aldehyde or aldehydes have flowed in , the temperature of the medium is raised to 120 - 150 ° c . in order to distill the reaction water and any water that has been introduced with the aldehydes . the reactor is then placed under a slight vacuum ( pressure of 0 . 2 to 0 . 6 bar , absolute ) and a temperature of 140 - 160 ° c . for a period that can typically vary from around 30 to 400 minutes , depending on the size of the reactor used and the equipment used to produce the vacuum . the tracking of the softening point temperature value during this period makes it possible to determine the stopping point of the resin . it is then possible to add a base like sodium carbonate , soda , or amines , for example triethanolamine , to neutralize the catalyst . the addition of a base is not obligatory but makes it possible to better control the development of the resin in the reactor . the reactor is then discharged and the resin is obtained . the catalysts used for synthesis of novolac resins may be any acid catalysts known to the person skilled in the art . suitable catalysts include mineral or organic acids , alone or in a mixture , sulfuric acid that is pure or in solution in alcoholic solvents , phosphoric acid , oxalic acid or formic acid . the catalyst quantities used generally vary from 0 . 4 to 0 . 1 %, based on the mass of alkylphenol ( s ). another object of the invention relates to the use of compounds as tackifying resins in the formulation in rubber . the novolac resins of the invention present the advantage of requiring little to no modification of the application conditions of the rubber formulation in which they are incorporated . yet the resins remain as effective as conventional resins and have a lower rate of free alkylphenol monomers , thus a reduced emission of harmful alkylphenol compounds when they are used . the determination of the rate of residual ptop is carried out using vapor phases chromatography on a hewlett packard 5890 series ii chromatograph equipped with an injector / divider , a cpv column , an fid detector and a recorder / integrator . the column is an ov1701 ® from ohyo valley ( length 30 m , internal diameter 0 . 25 mm , film thickness 0 . 25 μm ). the measurement is carried out isothermically at 180 ° c ., the period of analysis is 25 min . the injector temperature is 250 ° c ., detector : 250 ° c . in a 10 ml bottle , about 0 . 03 g of reference standard bht ( 2 , 6 - di - tert - butyl - 4 - methylphenol ) is weighed in , then about 1 g resin and finished with about 6 g rp acetone . the response coefficient is determined by injecting a ptop / bht standard under the same dilution conditions . this measurement is carried out according to standard e28 - 96 on an nba 440 ® or nba 430 device from the normalab company . operating method for examples 1 to 8 ( comparative ) and examples 9 to 11 ( according to the invention ) 500 g para - tertiary octylphenol and possible x g of stearic acid ( table 1 gives the quantity of stearic acid added as a percentage of the ptop introduced ) and 2 . 1 g catalyst ( sulfuric acid solution at 25 % in isopropyl alcohol ) is added to a 1 liter glass reactor equipped with a mechanical agitator and a refrigerant system in order to ensure an efficient reflux . the temperature of the medium is raised to 90 ° c . while agitating . the formaldehyde solution at 50 % in water is maintained at 60 ° c . and then allowed to flow in over a period of 30 to 45 minutes , while regulating the flow of formaldehyde in such a way as to maintain a temperature of 100 - 110 ° c . in the reactor . when the formaldehyde is finished flowing in , the assembly is modified in order to permit the distillation of the reaction water . then the temperature of the reaction medium is raised progressively toward 130 - 150 ° c . ( t1 in table 1 ) while distilling the water of the medium . this first phase lasts around one to two hours . the medium becomes thicker and foamy . when no more distillate remains , the temperature of the medium is raised progressively toward 150 ° c . while decreasing the pressure to 0 . 4 bar absolute to finish the removal of the water in the medium ( i . e . the values t2 and p in table 1 ). at the end of 20 minutes , 1 . 4 g of triethanolamine ( diluted with 1 . 4 g of water ) is introduced into the reactor , an aliquot sample is taken from the reactor in order to measure the softening point temperature . at this point , the resin is practically finished and does not advance more than 3 to 4 ° c . over several hours . when the desired softening point temperature is reached , the heating is stopped and the resin can leave the reactor for cooling , then analysis . * when the distillation of the residual ptop is carried out , it is necessary to operate at an elevated vacuum and temperature conditions that are otherwise undesirable from an industrial point of view . ** the medium becomes too viscous and the step in a vacuum cannot be carried out without the risk of filling the reactor with the expanding resin . it is only possible to operate step 1 at atmospheric pressure then transfer the resin . a mixture is made with fusion between a resin sold by schenectady international , inc . or ceca under the trade name r 7578p having a softening point value between 120 and 140 ° c . and a free ptop content of less than 1 % ( novolac resin obtained by condensation of ptop with formol ) with different fatty acids indicated in table 2 . 120 g of resin are melted at 140 ° c ., the fatty acid is then added , then the mixture is brought to 180 ° c . in order to ensure a homogeneous mixture within one to two hours . the resins according to the invention are introduced into a mixture for a sidewall with a height of 4 parts per cent of elastomer ( pce ) with polybutadiene ( br ) base and polyisoprene ( ir ) according to the following composition : 60 pce of br 1 . 4 cis sold by bayer under the name buna cb 10 , non - staining , with viscosity ml ( 1 + 4 ) of 42 - 53 at 100 ° c . and of which the amount of 1 . 4 cis is 96 %, 40 pce of ir 1 . 4 cis sold by goodyear under the name natsyn 2200 with viscosity ml ( 1 + 4 ) of 70 - 90 at 100 ° c ., 60 pce of carbon black sold by degussa under the name corax n550 , with average diameter 47 m . c . and weight per surface area of 43 m 2 / g , 5 pce of aromatic oil sold by bp under the name enerdex 65 with density 0 . 984 at 20 ° c . and with viscosity 25 . 5 cst ( mm 2 / s ) at 100 ° c ., 5 pce stearic acid ( activator ), 5 pce zinc oxide , 2 pce anti - ozone and anti - aging protection agent ( n - isopropyl - n ′- phenyl - p - phenylene - diamine ( ippd )) sold by bayer under the name vulkanox 4010 na by bayer , 2 pce of vulkanox 4020lg , anti - ozone and anti - aging protection agent n -( 1 , 3 - dimethyl butyl )- n ′- phenyl - p - phenylene - diamine ( 6ppd ) from bayer , 4 pce of tackifying resin from example 11 or tackifying alkylphenol / formol resin with melting point temperature of 102 ° c . sold by schenectady international , inc . or ceca under the trade name r 7521p , 1 pce insoluble sulfur ( vulcanizing agent ) sold by flexys under the name crystex ot20 , containing 78 % total sulfur , and 1 . 5 pce of n - cyclohexyl - 2 - benzothiazyl sulfonamide ( cbs ). the base mixtures or master mixtures ( non - accelerated mixtures ) are prepared in a banbury type internal mixer with 390 cm 3 capacity . it is important to note that the speed of the rotors , as well as the starting temperature have been determined in such a way that the dropping temperature of the mixture reaches at least 135 ° c . within a convenient time ( 10 min ). the gum and half the oil and carbon black are introduced at the same time , then the resin is ground a second time with the rest of the oil and of the carbon black . the mixtures are refrigerated immediately in a mixer with cold cylinders . after resting 24 h , the base mixtures are accelerated in the internal mixer . the initial temperature of the chamber is 50 ° c . and the speed of the rotors is 50 rpm . the mixing cycle is 6 minutes and the dropping is carried out at 100 ° c . to prevent any risk that the mixture will burn . the forming is then carried out on cylinders at 70 ° c . when the final mixtures are cooled , samples are cut off and stored protected from light and in an atmosphere with controlled temperature ( 23 ± 2 ° c .) and humidity ( 53 ± 3 % rel . hum .). storage is carried out in petri boxes ; the samples are placed on sheets of paper since they adhere quickly and strongly to glass . this measurement is a measurement of traction on two disks of crude rubber in contact , and is carried out on an instron dynamometer ( model 5565 ), equipped with the control software described below . the tack measurement assembly diagram is shown in fig1 . circular samples ( diameter 18 mm , thickness 2 mm ) are glued to steel disks and put in place in the two mounting plates . the lower mounting plate is fastened and the upper is mobile and controlled by the control software . it lowers up to the application of a specific pressure pc for a specific time tc , then it rises , measuring the force required to pull the two samples apart . the profile measurement carried out by the control software is made up of five ramps : 1 st ramp : displacement of frame until pc is reached ( speed = 5 mm / min ), 2 nd ramp : maintaining pc for tc , 3 rd ramp : raising the frame again at slow sped to return to a compression force zero . variation in force of pc + 2n ( speed = 0 . 1 mm / min ), 4 th ramp : maintaining frame for 300 s , the rubber relaxes , the force is returned to zero , 5 th ramp : raising of the frame at constant speed set at 2 mm / min . during the entire cycle , the computer registers the force as a function of displacement , time , and tack measurement profile , as shown in fig2 . during the traction phase , the following significant values are recorded : the maximum traction force , and the area under the curve giving the force as a function of displacement , called adherence energy . the conditions used for this manipulation are pc = 20 n and tc = 20 x . the tack measurements presented in table 3 were carried out 1 day after acceleration . the results show that the performance of this resin is at least as good as the standard resin with a comparable softening point temperature , e . g . the resin r 7521p sold by schenectady international , inc . or ceca that contains more than 3 % free ptop .