CA1283818C - Resilient coat for tie of direct-connection type track - Google Patents

Abstract

Title of the Invention:
RESILIENT COAT FOR TIE OF DIRECT-CONNECTON TYPE TRACX

Abstract of the Disclosure:
A resilient coat for a direct connection-type tie (Danchoku tie) which is composed of a concrete tie body and a microcellular polyurethane elastomer coating layer which adheres to and coats the lower portion of the tie body to form an integral body therewith, and said microcellular polyurethane elastomer having urethane bonds and a bulk density of 0.4-0.75 g/cm3 and being prepared from the start-ing foamable liquid of urethane elastomer composed substan-tially of (a) a polyether polyol having an average number of functional groups of 2.5-4.5 and a number average molecular weight of 2000-8500, (b) a vinyl monomer-grafted polyol having an average number of functional groups of 2.5-4.0, and the graft ratio of 4-20% by weight, (c) a liquid poly-butadiene polyol having hydroxyl terminal group(s), an average number of functional groups of 2.0-3.0 and a number average molecular weight of 2000-7000, (d) an organic poly-isocyanate, (e) a chain extender, (f) a blowing agent, and (g) a urethanation catalyst, at such ratios that the NCO
index is within the range of 90-110, and the concentration of the chain extender, based on the total amount of the five components of (a), (b), (c), (d) and (e), being 0.3 X 10-3 to 1.5 X 10-3 mol/g.

Description

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This invention relates to a ~ie for railway track.
More specifically, the in~ention relates to a resilient coat for a direct-connection type ~ie composed of a concrete tie body or supporting rail (~Danchoku~ tie) with its lower portion coated by a layer of a microcellular polyure hane elastomer which is adhered to ~he former to form an integral body, said Danchoku tie achieving easier maintenance and reduction in railway vibration and noise at the same timel and furthermore allowing laying of railway track with high precision and easy operation.
Due to mainly the demand for elimination or reduc-tion of labor, the recent trend is that the conventional ballasted tie track is being replaced by direct-connection type track system such as one using track slab, which is easier of maintenance. In this direct-connection type track system, however, concrete slabs were directly laid on solid roadbed without using ballast and ballast-mat, and consequ-ently there may be such drawbacks as increased railway vibration and noise compared with the case of using resi-lient ballasted track with ballast-mat.
Accordingly the development of a new system which is easier of maintenance and furthermore causes less railway vibration and noise has been demanded. To meet this demand, so-called n resilient coated tie", i.e., larger size concrete tie (namely, a track slab of reduced size) with its bottom and side surfaces coated with an elastomeric material, was proposed, and the so-called direct connection type resilient coa~ed tie system was studied~ with the view to reduce the vibration transmission and occurrence of noisey by laying such ties on concre~e roadbed ~hrouyh a grout (for example, synthetic resin, grouting concrete~ etc.~.
AS the elastomeric material to be used for the resilient coated tie, it was proposed in ~he past to use the product obtained through the steps of mixing the pulverized rubber obtained from used automobile tyres with a poly-urethane adhesive, filling a mold with the mixture, pressing the latter with a compresser and aging the same under heat-ing. However, preparation of such a resilient material requires much labor (production efficiency: one piece of the product per mold and per day) as well as large scale eyuip-ments, and besides, the adh~sion of the resili~nt coating to concrete tie bodies is apt to become incomplete, occasion ally causing peeling off. Furthermore, in case of laying the conventional resilient coated ties on concrete roadbed and burying and fixing them with grouting concrete in situ, the resilient material is almost completely bound to the concrete and prevented of free deformation. Hence, the spring constant increases, the vibration-isolating effect is reduced and the meeit of using the resilient coat is lost.
Thus, in the system of burying and fixing ties in and on concrete roadbed using, for example, grouting con-crete (~Danchokuq track) for reduGing vibration and n`oise,the vibration-isolator coat is firmly confined by the grouting concrete and inhibited of free deformation, and ~33~

for this reason the vibration isolator coat is required to still fully exhibit its vibration transmission-reducing effect and noise-reducing effect even under the free de-formation-restricted condition, as strongly adhered to the tie bodies and without an increase in tbe spring constant.
The property requirements on the resilient-coating material for Danchoku ties to be used in railway track, on which many-coach trains run at high speeds, are still more rigorous, e.g., the following property ratings are required:
Permanent compression set: 15% or less Spring constant: 0.2-2 tons/cm/100 cm2 Tensile strength: 5 kg f/cm2 or higher Tensile elongation: 100% or more Waterproofness (variation of tensile strength) : within +20%
(variation of tensile elongation) : within 20%
Alkali resistance (variation of tensile strength) : within +20%
(variation of tensile elongation) : within +20~
Fatigue resistance: amount of permanent deformation 1.0 mm or less.
It is required tbat the material should satisfy all of those re~uirements at the same time.
Furthermore, there is another important require-ment that the resilient or elastomeric coating material must strongly adhere to the concrete tie bodiest never peeling off under the repetitive compression exerted by intermittent train running.
The present inventors discovered and proposed, as an elastomeric coating material fully satis~ying these requirements, a microcellular urethane elastomer having a bulk density of 0.3-0.9 g/cm3, which is prepared from a raw foaming liquid of urethane elastomer composed of a poly-hydric alcohol having an average number of functional group Of 2.5-3.5 and a number average molecular weight of about 4500 - about 8500, an organic polyisocyanate~ a chain-ex-tending agent, a urethanation catalyst and a foaming agent, said raw liguid containing the chain-extending agent at a concentration of 0.2 X 10 ~ to 1.0 X 10 3 mol/g per the unit weight of the urethane elastomer (Laid-open Gazette, Kokai No. 130754/1980).
This previously proposed microcellular urethane elastomer satisfies the foregoing ratings, and is actually used at the straight portions of high-speed railway track.
It is only logical, however, that even with such elastomeric coating material composed of the microcellular urethane elastomer, it is preferred to reduce the cost of raw mate~
rials by further lowering the bulk density. Low bulk den-sity however inevitably reduces ~he spring constant. At the curved portions of railway track, furthermore, the track is subject to particularly high centrifugal force and the elastomeric coating material is severely compressed.

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Consequently spaces are formed between the elastomeric coating material and the grouting concre~e, and water and dust tend to go in~o said spaces. Therefore, it i8 inauf-ficient to simply raise the degree of foaming o said mi ro-cellular urethane elastomer ~o reduce its bulk density.
For example, there is a problem that if bulk density of the microcellular urethane elastomer is kept at not higher than 0.7 g/cm3 and still the spring constant is to be maintained at around 1.0 tf/ cm/100 cm2, the permanen~ compr~ssion set is increased.
Under the circumstances, an object of the present invention is to provide Danchoku ties of which elastomeric coating material is made of a microcellular polyurethane elastomer which, in spite of its low bulk density, shows no substantial increase in its permanent compression set.
Another object of the present invention is to provide Danchoku ties which enable very accurate and easy laying of Vanchoku railway track, by boring plural through-holes for bolting which vertically pierce through the Danchoku ties inclusive of the elastomeric coating.
Still other object and advantages of the present invention will become apparent from the following detailed explanation of the invention.
According to the present invention, a resilient coated, direct connection-type tie (Danchoku tie) which is composed of a concrete tie body for supporting rail and a microcellular polyurethane elastomer coating layer which adheres to and coats the lower portion of ~he tie body to form an integral body therewith, and is provided with two or more through-holes for bolting which vertically pierce through said tie body and coating layer, said ~ie body having buried in its through-holes the nu~s screw-fittable with the bolts, and said microcelluar polyurethane elastomer having urethane bonds and a bulk density of 0.4~0.75 g/cm3 and being prepared from the starting foamable liquid of urethane elastomer composed substantially of (a) a polyether polyol having an average number of functional groups of 2.5-4.5 and a number average molecular weight of 2000-8500, (b) a vinyl monomer-grafted polyol having an average number of functional groups of 2.5-4~0, and the graft ratio of 4-20% by weight, ~c) a liquid polybutadiene polyol having hydroxyl terminal group(s), an average number of functional groups of 2.0-3.0 and a number average molecular weight of 2000-7000, ~o (d) an organic polyisocyanate, (e) a chain extender, (f) a blowing agent, and (g) a urethanation catalyst, at such ratios that the NCO index i5 within the range of 90-110~ and the concentration of the chain extender, based on the total amount of the five components of ~a)~ (b), (c), (d) and (e), being 0.3xlO 3 to 1.5xlO 3 mol/g.

Hereinafter the tie involving present invention will be explained in further details, referring to the specific embodiments shown in -the attached drawings.
Figure 1 is a plan view of one embodiment of the -tie involving presen-t invention, Figure 2 is a section of the embodimen-t of Figure 1, cut along the line A-A, Figure 3 is a section of the embodiment of Figure 1, cut along the line B-B, Figure 4 is a vertical section illustrating the Danchoku tie of this inven-tion as temporarily laid on the under-structure of railway -track, Figure 5 is a vertical section illustrating the Danchoku tie of this invention as laid under the railway track, Figure 6 is a perspective view illustrating the mold fit on the concrete tie body in accordance with the present invention, Figure 7 is a section of the embodiment of Figure 6, cut along the line C-C, ~0 Figure 8 is a flow sheet showing production steps of the~Danchoku tie in accordance with the present invention, Figure 9 is an enlarged section of a portion of the mold around its deaeration holes, and Figures lOA and lOB are a side elevation and a sec-tion view, respectively, of a test -track laid with Danchoku ties.
As shown in Figures 1-3, the -tie involving present . invention is composed basically of the structure of a concrete tie body 1 for supporting rail, wi~h its lower portion adhered and coa~ed with a microcellular polyurethane elas-tomer coating layer 2, together forming an integral body~
In throughout the present specification and claims, the surface of the tie on which the rail i5 laid will be referred to as ~top", the surface opposite thereto, as "bottomN, and all other surfaces, as "sides~
The coating layer 2 coats the entire bottom and the lower portions of the sides of the concrete tie body, as shown in FigsO 2 and 3. In that occasion, the height h of the coating layers on the sides is not particularly limited, but can be varied over a wide range depending on the in-tended utility of the Danchoku tie (for high-speed railway~
ordinary railway, subway, etc.). Normally, however, the height h is advantageously from 1/20 to 1/1, preferably 1/4 - 3/4, inter alia, 1/2 3/5, of the height H of the con-crete tie body. And, for the ordinary concrete tie body having an H of 8-30 cm, recommendably the height h of coat-ing is 4-18 cm.
The thickness as w, w' of the coating layer 2 neither are limited, but are variable over a wide range depending on such factors as the intended utility of Danchoku tie. It is generally desirablet however, that it should be at least 8 mm. The upper limit of the thickness is not critical~ but generally that of 50 mm or less is sufficient, as too thick a coating layer is expensive and does not show advantages to justify the cost increase.

Thus, the coa~ing layer 2 normally can have a thickness of 10-35 mm, preferably 15-30 mmO Within said range, the thickness of coating layer 2 may be same at the bottom and at the sides, but the thickness w' at the sides subject to less load may be less than the thicknes~ w of the coating at the bottom of the tie, e.g., w may range 15-50 mm, prefer-ably 20-30 mm, w' 5-50 mm, pre~erably ~ -29 mm, and w - w', l-lû mmO
The size of concrete tie body to be coated with lo such a coating layer is variable depending on he intended use of the tie, but normally it is 50-1000 cm in width, 200-280 cm in length and 10-30 cm in height.
The most characteristic feature of the tle involv-ing present inven~ion resides in the provision of at least two through-holes 3, 3', 3" ... for bolting bored vertically through the concrete tie body 1 and coating layer 2 of Danchoku tie as described above, and of nuts 4 fittable with the bolts, which are buried in the through-hole portions of the concrete tie body 1.
As illustrated in Fig 4, into each of the through-holes 3, 3', 3" ... for insertion of bolts, holding bolts 6, 6', 6'' ... are screwed, to pierce through the tie. By the adjustment of these holding bolts, the three-dimensional position of the tie can be determined to lay the tie at the desired height with desired inclination of its top, with high precision and easy operationO
Such through-holes may be bored, as illustrated in 3~

Fig. 1, one ~ach in the vicinity of the two ends of one edge of concrete tie body 1 as 3 and 3n~ and one at the center~
in the ViCillity of the opposite edge, as 3', three in total.
Or, as shown with dotted line in Fig. 1~ instead of boring one hole 3' at the center of the portion near the other edge, two holes 3In~ 3~n may be bored at the corresponding positions to those of the holes 3, 3~ on said edge, making the total number of through-holes four~
The size of the through-holes is determined depending on the thickness of holding bolt to be inserted thereinto, while advantageously the diameter of 10-40 mm, preferably 20-30 mm is normally selected.
It is permissible to form a depression at the center of downmost portion of the bottom of the coating lS layer 2 composed of the microcellular polyurethane elastomer which is subject to less load, as shown in Figs. 2 and 3, and to fit into said depression, a soft synthetic resin foam 5 which is cheaper than the microcellular polyurethane elastomer. This enables to avoid the central reaction which poses a problem in the strength property of tie body, and to save the consumption of expensive microcellular polyurethane elastomer As synthetic resin foams useful for this purpose, closed cell type crosslinked polyethylene foams having an apparent density of normally 0.01-0.1, preerably 0.02-0.05 are particularly suitable.
The length of said depression 5t in Fig. 2) nor-mally ranges 1/4 - 1/2 of the length L of conrete tie body, ~3~

preferably 1/4 - 1/3. Within said range the length t is suitably variable. Also the depth (d in Fig. 2~ of the depression may range lJ10 - 1/1, particularly 1/2 - 7J10, of the thickness w o the coating layer 2 at the bottom. It is advantageous that the depression should be formed over the entire width direction of coating layer 2~ as fihown in Fig.
3.
The Danchoku tie involving this invention having the above-described structure can be laid under railway tracks in the manner described hereinbelow, as illustrated in Figs. 4 and 5.
Namely, holding bolts 6, 6', 6" ... are fitted with the nuts 4 buried in the through-holes 3, 3', 3" ~..
vertically piercing through the Danchoku tie involving this invention9 as bored in the concrete tie body 1, in such a manner that thP lower ends of these bolts should project out of the coating layer 2 of the tie at the bottom. The lower ends of the bolts are placed in the concrete crib 7 con-structed on the under-structure of the railway track, and by adjusting each bolt, the level and inclination of the top of tie body 1 can be determined (see Fig. 4).
Then on the top of concrete body 1, rails 8, 8' are fastened in accordance with the accepted practice, and into the spaces between the concrete crib 7 on the under-structure and the coating layer 2 at the lower portion ofthe concrete tie, grouting concrete is poured to form the solid bed 9. Before this concrete is ~ully cured, the ~3~

holding bolts 6, 6', 6" ... are removed~ and onto the tops of the through-holes 3, 3 ~ ~ 3n, . ~ . CapB made of an elas-tomer, 10, 10', lQ" ... are fitted (see Fiy. 5).
The tie involving this inven~ion thus having the holding bolts 6, 6', 6" ..~ screwed into and piercing through the through-holes 3, 3', 3" ... vertically extending therethrough, by adjusting said bol~s, the three dimensional position of the tie as will give the desired level and inclination of top surface thereof can be determined.
Accordingly it becomes possible to lay the railway track very precisely through easy operations.
In pouring the concrete, care should be taken that the concrete should not flow into the through-holes to directly connect the concrete tie body 1 with the bed 9.
Because, should they be directly connected, the vibration of concrete tie body 1 is directly transmitted to the bed 9, and cannot be absorbed and buffered at the coating layer 2.
Therefore~ it is important to keep the hole size, at least at the lower coating layer portion, at about the same or only slightly greater than the thickness of the bolt to be inserted thereinto, to substantially prevent the concrete from flowing into the hole.
From the same reason, the concrete for making the bed should not rise over the upper edges of the coating layer 2 at the sides of the tie, to be directly connected with the concrete tie body 1 ~see Fig~ S).
In short, it is very important that the concrete ~ ~ ~3 tie body 1 be substantial]y completely isolated from the concrete bed 9.
One of the characteris~ic features of Danchoku tie involving this invention is the use of specific micro-cellular polyurethane foam as the material for making thecoating layer.
That is, the present inventors discoYered that microcellular polyurethane elastomers are well suited as the coating material for Danchoku tie, which can exhibit vibration-isolating effect at the position intervening the concrete tie body and roadbed as well as the groutiny con-crete serving as the solid bed, because of the energy loss effect, etc~ based on their viscoelasticity characteristics.
Whereupon the present invention was completed. According to the present invention, the spring constant of Danchoku tie can be reduced to equal or even below that of the ballasted track, on rigid roadbed such as high level bridge, by a suitably selecting soft polyurethane elastomer, and whereby the vibration and noise caused by train running can be effectively isolated~ Furthermore, by the use of a micro-cellular polyurethane elastomer, it is made possible that even when the elastomeric coating material is confined by the grouting concrete serving as the solid bed, the marked reduction in the vibration-isolating effect due to the increase in spring constant can be prevented, as such an elastomer can be internally freely deformed.
The microcellular polyurethane elastomer to be ~g~:~3~

used in the present invention normally has a bulk density within the range of 0.4-0.7S g/cm3, preferably 0.55-0.7 g/cm3.
The physical and chemical properties of poly-urethane elas~omers other than the bulk density can bevaried over broad ranges by the selection of constituents~
but for the specific purpose of isolation of vibration as in the present invention, naturally the optimum constituent must be selected so as to attain the desired durability and vibration-isolating characteristics. Hereinafter the com-position of the polyurethane elastomer suitable for the purpose of this invention will be explained in detail.
The microcellular polyurethane elastomer to be used in this invention is formed from a specific starting foamable liquid of urethane elastomer composed of (a) poly-ether polyol, (b) vinyl monomer-grafted polyol, (c~ liquid polybutadiene polyol, (d) organic polyisocyanate, (e) chain-extender, (f) blowing agent and (g) urethanation catalyst.
The polyether polyol (a) to be used as one of the polyol components in the preparation of the polyurethane elastomer according to the present invention has an average number of functional groups of 2.5-4.5, and a number average molecular weight of 2000-8500. When the average numb~r of functional groups in the employed polyether polyol is less than 2.5, the foamed urethane elastomer obtained therefrom shows increased permanent compression set. Conversely when the average number of functional groups exceeds 4.5, the ~ 3 resulting elastomer shows a tendency to become harder, and furthermore the possibility of its rupture increases when it is exposed to the vibratory compression. Thus, the preferred average number of functional groups is 2.5-4.5, particularly 2.8-4Ø
Again, when the number average molecular weight of the polyether polyol (a) is less than 2,000, a foamed poly-urethane elastomer having a high vibration energy-absorbing characteristics can hardly be obtained. Conversely, when it exceeds 8,500, the resulting polyurethane elastomer shows degradation in its elastic properties, tends tu produce plastic deformation, and shows a strong tendency particu-larly for increased permanent compression set. Thus it is desirable for the polyether polyol to be used in ~he present invention to have the number average molecular weight nor-mally ranging from 2000-8500, particularly 3000-6500.
As such polyether polyol (a), those normally used in the preparation of polyurethane elastomers can be option-ally used. More specifically, such polyether polyols ob-tained by addition-polymerizing C2-C4 lower alkylene oxides, such as ethylene oxide, propylene oxide, etc. to C2-C6 aliphatic polyhydric alcohols such as glycerin, trimethylol-propane, etc. or to active hydrogen-containing compounds having active hydrogen atoms such as ethylenediamine, di-aminodiphenylmethane, etc. may be named. Typical examplesof such polyether polyols (a) include glycèrin/propylene oxide/ethylene oxide copolymerized adduct (average number of unctional groups = 3.0, number average molecular weight = 3000), propylene glycol/propylene oxide/ethylene oxide copolymerized adduct ~average number of functional gr~ups = 2~0, number average molecular weight = 4800), glycerin/
pentaerythritol/propylene oxide/ethylene oxide copolymeriæed adduct (average number of functional groups = 3.7, number average molecular weight = 5700), etc.
One of the characteristic features of the present invention resides in that, in combination with th~ above polyether polyol (a), a vinyl monomer-grafted polyol ~b) having an average number of functional groups of 2.5-4.0 and the graft ratio of 4-20% by weight, and a liquid polybutadiene polyol (c) having an average number of functional groups of 2.0-3.0, a number average molecu-lar weight of 2000-7000, and hydroxyl terminal group(s), are used as the polyol component for composing the foamed polyurethane elastomer.
The "vinyl monomer-grafted polyols" to be used in the present invention (hereinafter may be referred to as the graft polyols) (b) signifies modified polyols prepared by in situ radical polymerization of vinyl monomers in the presence of ordinary polyols, which ~er se are known as the polyol component for producing high elasticity urethane foams (e.g., Japanese Patent No. 447628, U.S. Patent No.
3033841, U. K. Patent No. 874130, German Patents Nos.
1077430, 1105179, 1081917, and 1111394, Laid-open Japanese Patent Publication No. 93729~81). According to the invention, of such graft polyols, particularly those spe-cific graft polyols having an average numher of functional groups of 2~5-4.0 and a graft ra~io of 4-20% by weight are usedO
When the average number of functional groups of the graf~ polyol employed is less than 2OS, the resulting microcellular polyurethane elastomer ~bows exc~ssively great permanent CQmpresSion set, and therefore is not appropriate.
Conversely9 when it exceeds 4.0, the product urethane elas-tomer shows a tendency to be hardened. The preferred range of the average number of functional groups of the graft polyol is 2.5-3Ø Again, when the graft ratio of the graft polyol is less than 4% by weight, permanent compression set is aggravated. Conversely, when it exceeds 20% by weight, the viscosity of the liquid rises to markedly deteriorate the moldability. Thus it is convenient that the graft ratio of qraft polyol ranges 4-20% by weight, particularly 5-15%
by weight. The term "graft ratio" used herein means, of the total vinyl monomer added, the ratio of the vinyl monomer graft polymerized to the polyol, to the weight of said polyol.
As the polyols to serve as the trunks of such graft polyols (b), those having a number average molecular weight of 2500-8S00, preferably 4000-7000, and a hydroxyl value of 20-67, preferably 24-50, are advantageously used.
For instance, polyalkyleneether glycol having a number average molecular weight of 4800v which is obtained by 3~

addition polymerizing ethylene oxide and/or propylene oxide to glycerin~ may be used~
As the vinyl monomers to be grafted to these polyols, the following may be named for example: olefins such as s~yrene, vinyltoluene, l-butene, 2-hexene, 1,4-hexadiene, lt3-butadiene and 3-pentene; vinyl halides such as vinyl chloride and vinylidene chloride; ethylenic un-saturated carboxylic acids, such as acrylic acid and meth-acrylic acid, or their derivatives (e.g., alkyl esters);
vinyl acetate; acrylonitrile; etc. They may b~ used either singly or in combination of more than one kind of the mono-mers.
The grafting of the above vinyl monomer or mono-mers to the above polyol can be achieved by radical poly-merizing the vinyl monomer~s) in the presence of the polyolaccording to the method known ~ se. As the useful radical polymeriza~ion catalyst, for example peroxide-type, azo-type or redox-type polymerization initiators or metal compound catalysts, etc.~ may be named. Thus obtained graft polyols can normally have the number average molecular weight of 2500-8500, preferably 4000-7000.
As the particularly preferred graft polyols for the present invention, for example, that obtained by graft polymerizing acrylonitrile and styrene to the polypropyl-eneether glycol having a number average molecular weight ofabout 5100 and an average number of functional groups oE
about 3, in an autoclave at 120C for 8 hours, using as the ~3~

polymerization initiator azobisisobutyronitrile, may be named.
"Liquid polybutadiene polyol" (c~ signifies liquid butadiene homopolymers or copolymers having terminal re-active hydroxyl groups, particularly allyl-type primary hydroxyl groups, which per se have been known (e.g., see U. S. Patents Nos. 3427366 and 3674743). They can be pre-pared by, for example, radical addition polymerizing 1,3-butadiene alone or 1,3-butadiene and no more than 75% by weight of the total monomer of C2-C12 ethylenically un-saturated monomers such as styrene, acrylonitrile, vinyl acetate, etc., in the presence of hydrogen peroxide as the polymerization catalyst.
According to the present invention, of such liquid polybutadiene polyolst particularly those having an average number of functional groups of 2.0-3.0 and a number average molecular weight of 2000-7000 are used. When the average number of functional groups in the liquid polybutadiene polyol employed is less than 2.0, product of high spring constant is difficult to be obtained. The product further-more shows a tendency to have larger permanent compression set. Also the miscibility thereof with the polymer polyol (a) and graft polyol (b) to be used as mixed therewith is impaired, and the moldability becomes markedly poor. Con-versely, when it exceeds 3.0, the product lacks elasticity,becomes brittle, is void of improvement in waterproofness and alkali resistance, and shows markedly depressed fatigue resistance.

Thus the convenient average number of functional groups of the liquid polybutadiene polyol (c) i within the range of 2.0-3.0t particularly 2.1-2.8. Again, when the number average molecular weight of the liquid polybutadiene polyol is less than 2,000, the variations in strength and elongation used as the norms of waterproofness and alkali resistance are markedly increased, and the fatiyue resistance and permanent compression set show strong tend-ency for marked degradation, and the closed cell-forming ability is reduced. On the other hand, when it exceeds 7,000, the viscosity of the liquid becomes excessiYely high, impairing its blendability with polyisocyanate (d).
Thus the product elastomer exhibits not only low tensile strength, bu~ fails to have a high spring constant, and shows poor closed-cell-forming ability. Thus it is ap-propriate for the liquid polybutadiene polyol to have a number average molecular weight of 2000-7000~ preferably 2400-5000.
Furthermore, it is desirable that the liquid polybutadiene polyol (c) to normally have a hydroxyl content of 0.5-1.0 milliequivalent/gram~ and an iodine value of 400-500.
As the particularly preferred liquid polybutadiene polyol, for example, a hydroxyl-terminated butadiene homo-polymer havin~ an average number of functional groups of2.2-2.4 and a number average molecular weight of about 2~800 (e.g., poly bd R-45 HT manufactured by ARCO Chemical Co.~, ~ ~ ~3 a hydroxyl-terminated butadiene/styrene copolymer having an average number of functional groups of 2~2-2.4 and a number average molecular weight of about 3,500 (e.g., poly bd CS-15 manufactured by ARCO Chemical Co.), and a hydroxyl-termi-nated butadiene/acrylonitrile copolymer having an averagenumber of functional groups of 2.5-2.8 and a number average molecular weight of about 4450 (e.g~, poly bd CN-15 manu-factured by ARCO Chemical Co.) may be named.
The blend eatio of the above-mentioned three types of polyol components (a), (b) and (c) is variable over a wide range, according to the physical properties required for the ultimately produced urethane elastomer. Normally7 it is convenient to select the blend ratio from the below-specified ranges, based on the total weight of the three components (a), (b) and (c).

Normal Preferred Optimum Polyol component range range range (wt%) (wt~)(wt%) (a) 15-95 20-95 50-90 (b) 1-60 1.5-40 2-30 (c) 1-50 2-40 3-30 Also the mixing ratio of the graft polyol (b) to the polybutadiene polyol (c), (~)/(c) by weight, is normally from 1/0.5 to 1/1.5, preferably from 1/0.8 to 1/1.2. The mixing ratio of the polyether polyol (a) to the polybuta-diene polyol, (a)/~c) by weight, is advantageously within the range of 3/1-15/1, preferably 4/1-10/1.

... .

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The urethane elastomer obtained by the concurrent use of vinyl monomer-graf~ed polyol tb) and liquid polybuta-diene polyol (c) in accordance with the present invention is found to achieve the novel effects unattainable with con-ventional elastomers, i~e., it gives a high spring con~tant,showing no degradation in tensile strength due to decrease in bulk d~nsity, even under the condi~ions of high loads and restricted deformation such as in the use for Danchoku ties, and furthermore its permanent compression set is small, and its variations in strength and elongation shown in the waterproofness and alkali resistance tests are small.
Preferred combination of the graft polyol (b) and the liquid polybutadiene polyol (c) for achieving the high quality closed cells, low variations in s~rength and elon-gation in the waterproofness and alkali resistance tests,excellent vibration-absorbing ability and appropriate spring constant and elongation, which are obtained as the novel, synergistic effect characteristic to the present invention, is that of the graft polyol having a graft ratio of 10-15%, a number average molecular weight of 5000-7000 and an aver-age number of functional groups of 3.0-3.8, with the liquid polybutadiene polyol having a number average molecular weight of 2500-4800 and an average number of functional group~ of 2.2-2.8, at a blend ratio of (b) to (c) within l:O.S to 1:1.5, particularly 1:0.8 to 1:1.2. Furthermore, the best synergistic effect is obtained when the above liquid polybutadiene polyol i5 blended in an amount of 3-30%

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by weight based on the total weight of the three types of polyol components (a), ~b) and (c).
As the organic polyisocyanate (d) to be r~acted with the above polyol components la), (b) and (c), any of those normally used for the production of urethane elas-tomers can be used. Examples are such polyisocyanates as 4,~'-diphenylmethanediisocyanate (M.D.I.), naphthylenedi-isocyanate, tolylenediisocyanate and hexamethylenediiso~
cyanate, which may be used either alone or in combination~
The ~olyisocyanate (d) may also be used in the form of a precursor obtained by ~dvance condensation with aforesaid polyhydric alcohol, i~e., a pre-polymer or a semi-pre-polymer.
In either case, the amount of the organic poly-isocyanate (d) i~ variable within the range around stoi-chiometric equivalent to the total active hydrogen-con-taining components (polyol components, chain extender, etc.) which are to react with the isocyanate residual groups (-NCO) present in the foamable starting liquid of urethane elastomer, +10%, i.e., in terms of NCO index, within th range of 90-110, preferably 9S-105.
The chain extender (e) to be used for the Eorma-tion of polyurethane elastomer in the present invention reacts with the organic polyisocyanate (d) to ~orm, by means Of a urethane bond or a urea bond, a hard segment that is principally an inter-hydrogen bond. It is thus an important factor controlling the elasticity characteristics of the product polyurethane elastomer. According to the invention, relatively low molecular weight, substantially difunctional active hydrogen-containing compounds are advantageously used as the chain extender. Examples of such a chain extender (e) includes C2-C10 diols such as ethylene glycol, propyl~ne glycol, propanediol, butanediol, hydroquinone and hydroxy-ethylquinone ether; and amines such as methylenebis(o-chloroaniline~, quadrol, ethylenediamine and triethanol-amine. They may be used ei~her alone or in combination.
According to our studies, in the combined use of the chain extender (e~ with aforesaid polyol components (a), (b) and (c), it is found appropriate to use the chain ex-tender ~e) at a concentration within the range of 0.3 X 10 3 mol/g to 1.5 X 10 3 mol/g, based on the total amount of the five components of (a), (b), (c), ~d) and (e). At a con-centration lo~er than thatp the chain-extending effect is insufficient, and the resulting foamed polyurethane elas-tomer generally shows the tendency to have low strength.
Conversely, at the chain extender concentration higher than 1.5 X 10 3 mol/g, inter-hydrogen bonds increases exces-sively, and as the result the resulting elastomer tends to become very hard, although is improved in strength. Such is rather undesirable for the product's utility as in the present invention, wherein the product is exposed to per-manent compression set and repetitive compression stress.The preferred concentration range of the chain extender is thus from 0.5 X 10 3 mol/g to 1~2 X 10 3 mol/g.

~33~

As the urethanation catalyst (g), any of those normally used in urethanation reaction, for exa~ple, tertiary amine compounds, organometal compounds, etc. may be used. Specific examples include triethylenediamine, diazabicycloundecene, n-methylmorpholine, N,N-dimethyl-ethanolamine; tin octylate and dibutyl tin laurate. The amount of the catalyst is not critical, which is variable over a wide range depending on the desired reaction rate.
It needs be suitably adjusted, however, according to the degree of foaming in the urethane elastomer and ambient conditions (temperature, humidity, etc.). Adjustment of the amount of catalyst has been a routine practice in the art, and the selection of suitable amount should be easy.
According to the present invention, foamed polyurethane elastomers are used. As the blowing agent (f) to be used for the production of the foamed bodies, conventional blowing agents, such as water and halogenated hydrocarbons (e.g., trichlorofluoromethane, methylene chloride, etc.) may be used. Although the degree of foaming of the urethane elastomer desired in the present invention is not strictly limited, it is important that the product should be relatively lowly foamed compared with ordinary urethane foams. Normally it is advantageous to achieve the degree of foaming, as expressed in terms of bulk density, 2~ ranging from 0.4-0.75 g/cm3, preferably 0.55-0.7 g/cm3. The amount of the blowing agent (f) and/or the degree of foaming can be eegulated to make the bulk density of the resulting ~ ~ ~3 urethane elastomez a value within the above-specified range.
Besides the foregoing, the starting foamable liquid of urethane elastomer in accordance with the present invention may contain, if required, a foam stabilizer (e.g., silicone surfactant), pigment(s) (e.g., carbon black, titanium oxide, etc.), dyes (e.g., Indanthrene dyes), other fillers (e.g., coal tar, inorganic or organic staple fibers such as glass fiber, asbestos fiber, nylon filer, vinyl chloride fiber, polyes~er fiber, acrylic fiber, natural or synthesized rubber powder; siliceous sand, etc.).
For the microcellular polyurethane elastomer to be used in this invention to function as a vibration isvlator;
its spring constant per the unit area is desirably about 0.2 ton/cm/100 cm2 or higher, particularly within the range of 0.7 ton/cm/100 cm2 - 2 tons/cm/100 cm2. The spring constant within said range can be obtained with the microcellular polyurethane elastomer having a thickness of 5 to 100 mml the thickness normally employed for a vibration-isolating layer, by suitably selecting its composition and bulk den-sity.
The microcellular polyurethane elastomer coating material exhibits excellent effects when it is integrally shaped with the concrete tie body and foamed and intimately adhered thereto. Or, its vibration-isolating effect can be effectively exhibited by shaping it separately from the concrete tie body and then adhering it to said body. That is, the coating layer may be adhered to the lower portion of the concrete tie body with an adhesive, or a box-type poly-urethane elastomer shaped body may be formed in advance and into which the concrete tie body may be inserted.
According to the presen~ invention, however, it is found that the most preferred embodiment for forming the coating layer comprises injecting a raw liquid for making the polyurethane elastomer around the lower portion of the concrete tie body in a box of a fixed size, and foaming the liquid to cause an integral shaping and foaming thereof with the tie body, to cause the former to adhere and coat the latter.
And, according to another aspect of the present invention, a process for manufacturing a Danchoku tie is provided, which comprises fixing a concre~e tie body in a mold in such a manner that the bottom and at least the lower portion of sides thereof are substantially completely encased in the mold leaving a certain space from the bottom and each of side walls, injecting into said space a foamable starting liquid of polyurethane elastomer of the aforesaid composition, and foaming and curing said starting liquid to integrally form a Danchoku tie coated with a microcellular polyurethane elastomer firmly adhered to the lower portion of the tie body.
According to the process of this invention as above-described, it is possible to make the Danchoku tie with ease, using an atmospheric injection type simple mold, and furthermore the shaped product can be released from the ~ ~ ~3 mold after about 2 hours feom the injection which requires only about 1 minute. Thus the production efficiency can be drastically increased. Furthermore because in the Danchoku tie prepared in accordance wi~h the subject integral shaping method the concrete tie body and the polyurethane elastomer coating material strongly adhere to each other, use of an adhering primer is unnecessary and hardly any peeling takes place.
According to the process of present invention, the aforesaid components of the starting foamable liquid of polyurethane elastomer are intimately mixed immediately before the injection in accordance with the accepted prac-tice, and injected into the mold for the integral shaping of the Danchoku tie. The mold is fixed to ~he concrete tie body in such a manner that the bottom and at least the lower portion of the sides tthe portions near the bottom) of the tie body should be substantially completely encased by the mold leaving a certain space therebetween, so as to enable the integral shaping of the Danchoku tie. One specific embodiment of mixing means is illustrated in Figs. 6 and 7. As shown in Figs. 6 and 7, a box-type mold 13 is at-tached to the concrete tie body 1 in such a manner that the bottom 11 and the lower portion of sides 12 of the body 1 can be substantially completely encased thereby. In that occasion, spaces s of the width w and w' are provided between respectively the bottom 11 of body 1 and the in-ternal bottom surface of the mold and between the sides 12 ~3~

of body 1 and the Lespective internal sides of the mold, w and w' corresponding to the required thicknesses of the coating layer. The mold 13 must be capable of encasing the concrete ~ie body 1 substantially completely so as to sub-stantially prevent leakage of the starting polyurethaneelastomer liquid which is to be injected into the space s.
In the mold, projections are formed at the locations cor-responding to the through-holes 3, 3', 3" ... in the con-crete tie body so as to form the through-holes also in the coating layer.
The height _ with which the mold 13 encases the sides 12 of concrete body 1 is made ~he same with the height h of the coating layer covering the sides 12 of body 1.
After the mold is set as above, a starting foam-able liquid of polyurethane elastomer is injected into thespace s through an injection inlet 14 provided at a suitable position of the mold 13. According to the studies of present inventors, the injection can be performed most advantageously when the concrete tie body combined with the mold 13 is given such a posture that, referring to Fig. 6, the side of the mold provided with the injection inlet 14 becomes the downside and the side of the mold having the deaeration holes 15 comes to the top, so that the bottom 11 stands substantially perpendicularly.
Fig. 8 is a flow sheet showing the injection operation of such a starting foamble liquid of polyurethane elastomer into the mold 13. The concrete tie body 1 mounted with the mold 13 is placed with i~s bot~om 11 standing nearly perpendicularly as aforesaid, and ~he starting-liquid is injected through the inlet 14 loca~ed at a lower portion of the mold 13. As the injection progresses, the air in the space s is driven out of the deaeration holes 15.
This starting foamable liquid of polyurethane elastomer can be formulated, for example, by separately feeding a liquid A composed of a polyether polyolt graft polyol, liquid polybutadiene polyol, chain extender, blowing agent, urethanation catalyst and a foam stailizer, etc~, and a liquid B composed of organic polyisocyanate into respec-tively the tanks 20 and 20', and therefrom supplying them via measuring pumps 21 and 21'~ respectively, into the two-liquids blender 22 and whereat intimately mixing the two li~uids. The liquid mixture is then led to the injection inlet 14 through the conduit 23 having a terminal valve 24.
The typical compositions of the liquids A and B
conveniently used in the present invention are as follows.
Composition of liquid A Parts by weight Polyether polyol 100 (glycerin/propylene oxide/
ethylene oxide copolymerized adduct average number of functional groups: 3-4 number average molecular weight: 2,000-7,000).

~3~

Graft polyol lO-~0 [a polymer polyol obtained by graft polymerizing acrylonitrile and styrene to glycerin/propylene oxide/
ethylene oxide copolymerized adduct (number average molecular weight = 5100), in the presence of azobisisobutyronitrile (polymerization initiator);
average number of functional groups = 3 graft ratio = 10%
number average molecular weight = 6000]
Liquid hydroxyl-terminated polybutadine polyol 5-20 Ethylene glycol 5-15 Water l.0-1.5 Triethylenediamine 0.5-2.0 Composition of li~__d BNCO index Polyisocyanate polyol prepolymer 90-llO
le.9. an isocyanate-terminated precursory precondensatioll product of 4,4'-diphenylmethanediisocyanate with glycerin/propylene oxide/
ethylene oxide copolymerized adduct (number average molecular weight = 6500, average number of functional groups = 3);
free NCO content = 16 wt~]

~ ~ 8~

The injection of the foamable starting liquid of polyurethane elastomer into the mold can be performed at a rate of normally 1-100 kg/min; preferably 30-60 kg/min. The amount to be injected may be varied within the range of 1/3 to 9/10 of the total volume of aforesaid space in the mold, depending on the desired deyree of foaming. The injected foamable starting liquid of polyurethane elastomer is then foamed and cured. The foaming and curing can normally be performed at room temperature, but if necessary it may be performed under heating to a temperature of up to about 70C. The foaming and curing terminates normally within 1-2 hours, and whereupon the mold is detouched from the concrete tie body.
Then a Danchoku tie coated with a microcellular polyurethane elastomer can be obtained. The cells in the microcellular polyurethane elastomer coating shaped in-tegrally with the concrete tie body are predominantly closed cells. The physical property desirably to be had by the elastomer are as follows:
(1) Bulk density: 0.4-0.75 g/cm3, preferably 0~55-0.7 g/cm3 (2) Permanent compression set:
not more than 15~, preferably not more than 5~

(3) Spring constant: at least 0.2 ton/cm/100 cm2, preferably 0.7-2 tons/cm/100 cm2, (4) Tensile strength: at least 5.0 kg/cm2, ~3~

preerably at least 10 kg/cm2 (5) Elongation: at least 100~, (6) Waterproofness: within ~20% in variation of tensile strength, preferably ~10%;
within ~20% in variation of elongation, preferably ~10%

(7) Alkali resistance: within ~20% in variation of tensile strength, preferably +10%;
within ~20% in variation of elongation, preferably ~10%

(8) Fatigue resistance: the amount of permanent deformation not more than l.0 mm, prefer-ably not more than 0.2 mm (9) Closed cell forming ratio: at least 90%, preferably 99-100~
The Danchoku tie manufactured by the subject process as above is composed of a concrete tie body 1 and a microcellular polyurethane elastomer coating material 2 adhered to the lower portion of said body 1 by the integral shaping, as illustrated in Figs. 1-3.
According to the studies of present inventors, it is found very convenient for ready release of the Danchoku tie from the mold,`~hat the deaeration holes 15 of the mold 13 each is given a cross-sectional shape of an inverse circular truncated corn spreading outwards as shown in Fig.
9. As the tapering angle ~ of the internal wall of each deaeration hole, that of 30-60 is normally suitable, - 3~ -particularly around 45. The inner diameter x of the de-aeration hole 15 in the mold 13 can be approximately 1-3 mm, and the length y of the cylindrical portion of said hole in the mold is preferably about 0.3-2 mm.
The Danchoku tie involving present invention as above-described exhibits excellent vibxation-isolating effect, and can drastically reduce the vibration and noise when used as the ties for railway track for high-speed trains, contxibuting to alleviate enviroNmental pollution caused b~ noise and vibration along railway lines.
Furthermore, the Danchoku ties involving present invention can be laid with high precision and easy opera-tions in the track-laying work, leading to marked reduction in labor cost and work period.
Furthermore, according to the preferred embodiment of the process of this invention, the microcellular poly-urethane elastomer coating material is integrally foamed and shaped with the concrete tie body, which advantageously brings about the strong adhesion of the coating to the concrete tie bodyO This high adherability is indeed a great practical advantage, as normally a vibration isolator is required to transmit the movements of the vibration source with certainty, to cut off the vibrations and absorb them within the isola~or.
Still in addition, according to the present invention the Danchoku ties (resilient coated ties) can he easily manufactured using a relatively simple apparatus; and ~ ~3 therefore fore the cost and energy consumption for the production can be decreased.
Hereinafter the subject Danchoku ties and the process for their production will be further explained with reference to the working examples.
Example A 400 mm x 2,000 mm x 200 mm concrete tie body 1 is set in a mold 13 having deaeration holes 15 of x = 1.5 mm~, in the manner illustrated in Fig. 6. The thickness of the coating layer (w, w') was 2S mm. Although not shown in Fig. 6, a partition wall was provided in the mold at the part suita~le for forming a depression or groove of 300 mm in width and 15 mm in depth at the central portion of the bottom plane of the coating layer, as shown in ~ig. 2. Then the liquid-~ A and B of the below-specified compositions were mixed in the stirrer 22 at a rotation rate of 6,000 rpm using the device illustrated in Fig. 8, and the mixture was injected into the space at the lower portion of the mold.
Leaving the system for the subsequent 2 hours at room tem-perature, the tie was parted from the mold. The physicalproperties of the polyurethane elastomer coating constitut-ing the resultant Danchoku tie are shown hereinbelow, to-gether with the compositions of the liquids A and B.
The physical properties were measured by the below-specified methods.
(1) Bulk density:
Measured in accordance with JIS Z 8807, "Method of measurement from volumen.
(2) Permanent compression set:
Measured in accordance with JIS K 6301 "10, Permanent Compression Set ~estn.
(33 Spring constant:
Measured in accordance with JIS K 6385 "5, Static Spring Constant Testn.
(A 10 cm X 10 cm X 2.5 cm test specimen is subjectd to a pressure of up to 425 kg, and the spring constant is determined between 100-400 kg on the load displacement curve.) (4) Tensile strength and elongation:
Measured in accordance with JIS K-6301, with Dumbbell test pieces No. 1 by "3. Methods of Tensile Testsn.
(5) Waterproofness:
The same Dumbbell test piece No. 1 used in the tensile strength test is immersed in distilled water or ion-exchange water for 96 hours, lightly wiped, and immediately subjected to the tensile strength test. The variation from the value before the aging is thus determined.
[6) Alkali resistance:
The same test method as that in above waterproofness is employed except that the immercing liquid is a 1~ (caustic potash/caustic ~3~

soda - 1:1) aqueous solution, and the immersing temperature is 50C.
(7) Fatigue resistance:
Measured in accordance with SRIS (Standard Rating of Japan Rubber Associa~ion) 3502. (Test conditions are: precompression amount 5 mm, vibration amplitude 4 mm, vibration frequency 5 Hz, repetition 1 x 106 times, and the size of test piece, 50 X 50 X 25 mm) (8) Closed cell foaming property:
Measured in accordance with ~ST~ D 2856-70 A.
Example 1 Composition of liquid A Parts by weight Polyether polyol (I~ 35 (glycerin/propylene oxide/
ethylene oxide copolymerized adduct average number of functional groups = 3, number average molecular weight = 3000) Polyether polyol (II) 40 (glycerin/pentaerythritol/
propylene oxide/ethylene oxide copolymerized adduct average number of functional groups = 3.7 number average molecular weight = 5,700) Graft polyol 15 [a polymer polyol obtained by graft polymerizing acrylonitrile and styrene to glycerin/propylene oxide/ethylene oxide copolymerized adduct (number average molecular weitht = 5100), in the presence of azobisisobutyronitrile (polymerization initiator) average number of functional groups = 3 graft ratio = 10%
number average molecular weight = 6000]
Hydroxyl-terminated liquid poly-butadiene polyol 15 (average number of functional groups = 205 number average molecular weight = 2750) Ethylene glycol 7 water 0-53 Triethylenediamine 0.7 Composit ~ N O index_ Polyisocyanate/polyol prepolymer 100 lisocyanate-terminated precursory condensation product of ~ a~ &~

4,4' diphenylmethanediisocyanate and a copolymerized adduct of glycerin/
propylene oxide/ethylene oxide having number average molecular weigh~ of 6500 taverage number of functional groups = 3), number average molecular weight = 6500) free NCO content = 16 wt~]
Physical properties:
Bulk density: 0.63 g/cm3 Spring constant: 1.5 tf/cm/100 cm2 Permanent compression set: 2.0%
Tensile strength: 13.0 kg/cm2 Elongation: 145g ~aterproofness Tensile strength variation: -0.9 Elongation variation: -0.3 Alkali resistance Tensile strength variation: -0.3%
Elongation variation: -0.2%
Fatigue resistance: amount of fatigue 0.26 mm Closed cell foaming property: closed cell formlng ratio 100%
25 Example 2 Composition of liquid A Parts by weight Polyether polyol ~II) 52 (glycerin/pentaerythri.tol/
propylene oxide/ethylene oxide copolymeriæed adduct average number of functional groups = 3.7 number average molecular weight = 5700) Graft polyol 15 la polymer polyol obtained by graft polymerizing acrylonitrile and styrene to glycerin/propylene oxide/
ethylene oxide copolymerized adduct (number average molecular weight = 5100), in the presence of azobisisobutyro-nitrile ~polymerization initiator);
average number of functional groups = 3 graft ratio = 10~
number average molecular weight = 6000~
Hydroxyl-terminate~ liquid polybutadiene homopolyol 12 (average number of functional groups = 2.3 number average molecular weight = 4700 hydroxyl content = 0.5 milliequivalent/g . .

~3~

iodine value = 450) Ethylene glycol 5~7 Water 0.48 Triethylenediamine 0~7 Composition of liquid B NCO index Polyisocyanate/polyol prepolymer 100 [an isocyanate-terminated precursory condensation product of 4,4'-diphenylmethanediisocyanate and glycerin/propylene oxide/ethylene oxide copolymerized adduct (number average molecular weight = 6500) free NCO content = 16 wt%]
Physical properties:

Bulk density: 0.69 g/cm Spring constant: 0.98 tf/cm/100 cm2 Permanent compression set: 3~8%
Tensile strength: 14.9 kg/cm2 Elongation: 210 Waterproofness Tensile strength variation: -3.7%
Elongation variation: -4.3%
Alkali resistance:
Tensile strength variation: -2.2%

Elongation variation: -4.1%
Fatigue resistance: amount of fatigue, 0.16 mm Closed-cell foaming property: closed cell forming ratio 99.9%

~3 The Danchoku ties prepared in the above Example 1 were laid for the test track as illustrated in Figs. lOA
and lOB, and their effects were measured as follows.
A part of the conventional ballasted track was removed from the test line set on Tohoku Shinkansen before opened to commercial operation, and Danchoku ties of Example 1 were laid over a length of 160 m. The Shinkansen train was used for the test, which was run at a speed of 200-210 km/h.
The vibration and noise caused by the train run-ning on the track were as shown respectively in Fig. lOB, as measured at the two points Vl and V2 (as to vibration) and at the three points of A, B and C (as to noise). The vibra-tion was measured with the baliumtitanate accelerometer and the noise, with the normal sound-meter.
The vibration- and noise-decreasing effects by the test track laid on the Danchoku ties of Example 1 as com-pared with the conventional ballasted track w~re as follows:
The vibration at Vl point (acceleration of rail) was nearly equal to that with the resilien~ ballas~ed track with ballast-mat, but at V2 point (acceleration of floor slab of elevated structure), it was decreased by 7dB. At point A (under the floor slab by 0.3 m) the noise was de-creased by 7d~ (A), at point B (under the floor slab by 5~0 m) it was decreased by 5dB(A), and at point (C) (under the elevated structure, 1.2 m high over the ground), by 4dB(A), as compared with the resilient ballasted track with ballast-mat~

Claims (23)

1. A resilient coat for a direct connection-type tie (Danchoku tie) which is composed of a concrete tie body and a microcellular polyurethane elastomer coating layer which adheres to and coats the lower portion of the tie body to form an integral body therewith, and said microcellular polyurethane elastomer having urethane bonds and a bulk density of 0.4-0.75 g/cm3 and being prepared from the starting foamable liquid of urethane elastomer composed substantially of (a) a polyether polyol having an average number of functional groups of 2.5-4.5 and a number average molecular weight of 2000-8500, (b) a vinyl monomer-grafted polyol having an average number of functional groups of 2.5-4.0, and the graft ratio of 4-20% by weight, (c) a liquid polybutadiene polyol having hydroxyl terminal group(s), an average number of functional groups of 2.0-3.0 and a number average molecular weight of 2000-7000, (d) an organic polyisocyanate, (e) a chain extender, (f) a blowing agent, and (g) a urethanation catalyst, at such ratios that the NCO index is within the range of 90-110, and the concentration of the chain extender, based on the total amount of the five components of (a), (b), (c), (d) and (e), being 0.3 X 10-3 to 1.5 X 10-3 mol/g.

2. The resilient coat of Claim 1, in which the poly-ether polyol (a) has an average number of functional groups of 2.8-4.0, and a number average molecular weight of 3000-6500.

3. The resilient coat of Claim 1, in which the poly-ether polyol (a) is selected from the group consisting of glycerin/propylene oxide/ethylene oxide copolymerized adduct (average number of functional groups = 3.0, number average molecular weight = 3000), propylene glycol/propylene oxide/ethylene oxide copolymerized adduct (average number of functional groups = 2.0, number average molecular weight =
4800), and glycerin/pentaerythritol/propylene oxide/ethylene oxide copolymerized adduct (average number of functional groups = 3.7, number average molecular weight = 5700).

4. The resilient coat of Claim 1, in which the vinyl monomer-grafted polyol (b) has an average number of func-tinoal groups of 3.0-3.8 and a graft ratio of 5-17% by weight.

5. The resilient coat of Claim 1, in which the vinyl monomer-grafted polyol (b) is a polyol having a number average molecular weight of 2500-8500 and a hydroxyl value of 20-67, to which at least one vinyl monomer selected from the group consisting of styrene, vinyltoluene, 1-butene, 2-hexene, 1,4-hexadiene, 1,3-butadiene, 3-pentene, vinyl chloride, vinylidene chloride, acrylic acid or methacrylic acid, their alkyl esters, vinyl acetate and acrylonitrile, is grafted.

6. The resilient coat of Claim 1, in which the vinyl monomer-grafted polyol (b) has a number average molecular weight of 4000-7000.

7. The resilient coat of Claim 1, in which the vinyl monomer grafted polyol (b) is the polypropyleneether glycol having a number average molecular weight of about 5100 and an average number of functional groups of about 3, to which acrylonitrile and styrene are grafted.

8. The resilient coat of Claim 1, in which the liquid polybutadiene polyol (c) has an average number of functional groups of 2.1-2.8 and a number average molecular weight of 2400-5000.

9. The resilient coat of Claim 1, in which the liquid polybutadiene polyol (c) has a hydroxyl content of 0.5-1.0 milliequivalent/g.

10. The resilient coat of Claim 1, in which the liquid polybutadiene polyol (c) is selected from the group consist-ing of hydroxyl-terminated butadiene homopolymer having an average number of functional groups of 2.2-2.4 and a number average molecular weight of about 2800, hydroxyl-terminated butadiene/styrene copolymer having an average number of functional groups of 2.2-2.4 and a number average molecular weight of about 3500, and hydroxyl-terminated butadiene/
acrylonitrile copolymer having an average number of func-tional groups of 2.5-2.8 and a number average molecular weight of about 4500.

11. The resilient coat of Claim 1, in which, based on the total weight of the polyol components (a), (b) and (c), 15-95% by weight of the polyether polyol (a), 1-60% by weight of the vinyl monomer-grafted polyol (b), and 1-50%
by weight of the liquid polybutadiene polyol (c) are used.

12. The resilient coat of Claim 1, in which the organic polyisocyanate (d) is selected from the group con-sisting of 4,4'-diphenylmethanediisocyanate, naphthylene-diisocyanate, tolylenediisocyanate and hexamethylenediiso-cyanate.

13. The resilient coat of Claim 1, in which the chain extender (e) is selected from the group consisting of ethylene glycol, propylene glycol, propanediol, butanediol, hydroquinone, hydroxyethylquinone ether, methylenebis-(o-dichloroaniline), quadrol, ethylenediamine and triethanol-amine.

14. The resilient coat of Claim 1, in which the chain extender (e) is contained in the starting foamable liquid at a concentration of, based on the total amount of the five components (a), (b), (c), (d) and (e), 0.5 X 10-3 mol/g-1.2 X 10-3 mol/g.

15. The resilient coat of Claim 1, in which the microcellular polyurethane elastomer has a bulk density of 0.55-0.7 g/cm3.

16. The resilient coat of Claim 1, in which the micro-cellular polyurethane elastomer has a permanent compression set of not higher than 15%.

17. The resilient coat of Claim 1, in which the micro-cellular polyurethane elastomer has a spring constant of not less than 0.2 ton/cm/100 cm2.

18. The resilient coat of Claim 1, in which the micro-cellular polyurethane elastomer has a tensile strength of at least 5.0 kg/cm2 and an elongation of at least 100%.

19. The resilient coat of Claim 1, in which the coating layer has a thickness of at least 8 mm.

20. The resilient coat of Claim 1, in which the coat-ing layer has a depressed part at the central portion of its bottom, said depressed part being fitted with a soft syn-thetic resin foam.

21. The resilient coat of Claim 20, in which the synthetic resin foam is a closed cell, cross-linked poly-ethylene foam.

22. The resilient coat of Claim 1, in which the coat-ing layer is adhered to, and coat, the lower portion of the concrete tie body, by the steps of injecting from the underside the starting foamable liquid of polyurethane elastomer into the mold encasing the lower portion of said tie body and foaming and curing the liquid in situ.

23. The resilient coat of Claim 20 in which said depressed part has a length of 1/4 to 1/2 that of the con-crete tie body.