referring first to fig1 the graph is self - explanatory and shows that a basically urethane composition can provide a primer layer which allows the marked area to be re - opened to the traffic , about 4 minutes and preferably about 6 minutes after the spreading of the composition at 100 ° c on the road pavement . the graph of fig2 comprises a curve i which illustrates the increase in viscosity ( η cp . 10 3 ) of a two component epoxy composition . curve ii illustrates how such increase can be improved by adding 30 % by weight of pre - polymers . curve iii illustrates the further improvement provided by the use of a three - component composition . curve iv illustrates the improvement provided by heating . as a matter of fact , said curve iv refers to the composition of curve ii , but at a temperature of 50 ° c . the ternary graph of fig3 is to be considered upon the premise that a pre - polymer ( as meant herein and in the appended claims ) can be produced by adding a given percentage of one co - reagent &# 34 ; a &# 34 ; to the other co - reagent &# 34 ; b &# 34 ;, and vice - versa , in regulated quantities . the graph is subdivided into areas by curves indicating the length of time necessary to attain the most desirable viscosity of 6 × 10 5 cp as a function of the temperature ( t ° ) in degrees centigrade and of the percentage of the pre - polymer formed by adding to a a certain percentage of b or vice - versa ( a + δ b , or b + δ a ), and taking into account the mass , in grams ( m g ), of the reacting composition . the diagonally hatched area defines the parameters to be satisfied for attaining such viscosity within 40 seconds and the cross - hatched area those for attaining the same viscosity within about 15 seconds . a few examples for compositions follow , indicated in parts by weight . this example describes the two components &# 34 ; a &# 34 ; and &# 34 ; b &# 34 ; adapted for forming a cross - linked epoxy - urethane primer layer . the specific actions and scope of certain components have been hereinbelow added , between brackets , for clearer understanding of the compositions and of their effects . ______________________________________ &# 34 ; a &# 34 ; urethane pre - polymer ( such as &# 34 ; adiprene l 315 &# 34 ; by dupont ) ( acting as wetting hydrophilousliquid ) 35epoxy resin ( such as &# 34 ; epon 828 &# 34 ; by shell )( acting as wetting liquid ) 15solid oxidized bitumen 50tar fractionated part for epoxy resin (&# 34 ; epoxytar &# 34 ;) ( acting as wetting and impregnatingliquid ) 15glycidil - ether of tercarboxylic acid ( actingas wetting and reactive liquid ) 5baryte ( acting as inorganic filler ) 15total parts 135 &# 34 ; b &# 34 ; 44 &# 39 ; methylene bis ( 2 - chloroaniline ( such as &# 34 ; moca &# 34 ;) ( solid ) 18low melting ( at about 40 ° c ) polyamide resin ( such as &# 34 ; versamid 100 &# 34 ; acting also as awetting agent ) 15solid oxidized bitumen 65 &# 34 ; epoxy tar &# 34 ; ( acting as wetting and impregnatingliquid ) 15dibutylphthalate ( acting as a plasticizer andwetting liquid ) 5baryte ( inorganic filler ) 17total parts 135______________________________________ this example describes a composition which is particularly suitable for preparing epoxy primer layers according to the &# 34 ; pre - polymer technique &# 34 ;. ______________________________________ &# 34 ; a &# 34 ; solid oxidized bitumen 15 &# 34 ; epoxy tar &# 34 ; 10hard kaolin ( such as &# 34 ; suprex clay &# 34 ;) 5colloidal silica ( such as &# 34 ; aerosil &# 34 ;) 2wetting , liquid epoxy resin ( such as forexample &# 34 ; araldite gy 250 &# 34 ; by ciba ) 68total parts 100 &# 34 ; b &# 34 ; solid bitumen 40 / 50 35 &# 34 ; epoxy tar &# 34 ; 15cresylic acid 15wetting and hydrophilous liquid amine ( suchas for example &# 34 ; alkamine lt &# 34 ; by anchorchemical ) 18hard kaolin 15liquid hydrophilous accelerator for epoxyresin ( such as &# 34 ; d m p 30 &# 34 ;) 2total parts 100______________________________________ the two - component composition of example 2 can advantageously be modified to a three - component one by injecting at or near the outlet of the machine , by means of a suitable mixer , 2 % by weight of the sum of the two components of tolylene diisocyanate , which promply reacts with the amidic function . the said &# 34 ; pre - polymer technique &# 34 ; of the invention can advantageously be made use of in an apparatus of the type shown in fig4 for supplying one or more outlets 10 from which the primer layer forming material m is ejected on the road pavement . the apparatus comprises a twin metering pump 12 actuated by a transmission 14 . the pump 12 feeds the components a and , b , respectively ( or vice versa ) into ducts 16 and 18 at equal rates ; these ducts comprise a twin valve system including a twin rotary valve 20 which provides controlled communication between by - pass ducts 26 , 28 and said passages 16 , 18 to discontinuing the supply when the downstream ducts 22 , 24 so that the components are kept circulating during the times in which the ejection of the primer layer forming composition is necessarily discontinued . by means of auxiliary ducts 30 , 32 , a suitable solvent is supplied such as from a pressurized supply tank ( not shown ) and injected into said passages 22 and 24 , the ejection being activated by electro - valves 36 , 38 controlled by thermostats 40 , 42 . a twin valve gear system 44 is located downstream of said passages 22 , 24 and comprises metering grooves or adjustable choking passages ( the adjustment being provided by axial shifting of said valve member 44 ) so that the flows into said passages 22 , 24 are each equally parted in &# 34 ; primary &# 34 ; flows progressing into downstream ducts 46 , 48 and &# 34 ; secondary &# 34 ; flows switched into other ducts 50 , 52 which , by means of cross ducts 54 , 56 , supply the said switched flows into the downstream ducts 48 and 46 , respectively . therefore , part of each primary flow is switched to form a secondary flow which joins the other primary flow , and vice versa . by adjusting the rates of such flows the formation of pre - polymers having the desired degree of polymerization is provided . the thus - mixed flows are fed into induction ducts 58 , 60 which join into an ejection head 62 including mixer means 64 to ensure the homogeneity of the ejected mixture . a simplified apparatus adapted to be associated with simple and lightweight road marking machines ( such as the machine described in the u . k . patent specification no . 1 , 421 , 483 ) is shown in fig5 . such apparatus comprises a container 70 divided into compartments 72 , 74 , each designed for processing and supplying an individual component a and b and each opening into a mixing chamber 76 . the processing , feeding and mixing are accomplished by screw means 78 and 86 driven by a pneumatic motor 80 , and the screw means to and 86 urge the mixture through an induction duct 82 and one or more outlets 84 . the compartments 72 , 74 are separated by a wall 88 provided with an aperture , preferably in the lower part of the apparatus , so that a rotor 90 , also driven by motor 80 and having radial vanes or blades , rotates in both compartments and carries metered amounts of the components from one to the other of said compartments , thus promoting the desired pre - polymer formation . both the apparatus of fig4 and that of fig5 are provided with means for ejecting residues of the reactive mixture from the outlet means and for cleaning the same when the operation is discontinued . said ejection and cleaning is favorably accomplished by feeding pressurized air and preferably solvents into said outlets 10 and 84 through a duct 92 connected at 94 to a source ( such as a pressurized tank , not shown ) of said pressurized air or solvent .