US3011412A - Safety marking system - Google Patents

Description

Dec. 5, 1961 T. L. HARRINGTON ErAL 3,011,412

SAFETY MARKING SYSTEM Filed April 11, 1957 /Z /0 I //lllllllg,

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47 @PNE/5 3,011,412 SAFETY MARKING SYSTEM Thomas L. Harrington, St. Paul, and Donald E. Pederson,

White Bear Lake, Minn., assignors to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a

corporation of Delaware Filed Apr. 11, 1957, Ser. No. 652,290 7 Claims. (Cl. 914-15) The marking of aircraft runways, streets, highways,

and the like, herein called traffic-ways, with appropriate visual safety indicia has increasingly become a serious problem in recent years because of the necessity for avoiding lengthy interruptions tothe iiow of traffic. Instead of lessening, indications are that this problem will become more and more serious as traic incre-ases.

It is now well recognized, from the `safety standpoint, that old marking methods which require rather lengthy interruption and re-routing of vtrafiic during the time of Iapplication, and for so long a period thereafter as may be required for drying, frequently create as many safety prohlerns as the resulting markings help to solve. Recently, some reduction of the time required for marking has been gainedkby the use of quick-drying materials, but v such materials frequently do not retain desired appearance According to our invention, painted safety markings of a Vandal-proof, highly durable andwear-resistant quality may be provided on traffic-ways Vwithout more than momentarily interrupting the flow of trac thereover. In fact, where safety markings, eg., cross-lane strips, yare tobe applied at an intersection controlled by semaphore signals, interference with the ow of trafliccan be `said to be substantially eliminated, inasmuch as the requisitev markings can be applied and made trafIic-sustaining during the time required for one or two changes of signal.

By practicing our invention, street markings are formed Y which have a characteristic new and novel structure, being in part durable, wearresistant and Vandal-proof, and in part temporary or passing. Almost immediately after being formed, our structures can withstand tratiic abra-sion fere more than momentarily with Athe flow of traiiic vhas i existed for many years, and while the preferred material for use in forming the temporary part of our structures has been known for years, no one to our knowledge has ever heretofore successfully presented the art withsuch applied thereover as a layer.

2 a rapid and eicient. -method of safety marking as herein set forth.

Our invention also introduces considerable economy in the art of providing superior safety markings for traffic-ways; and in this respect, it will be of great benefit tothe taxpaying public.

The Vandal-proof, durable and wear-resistant portion of our safety marking structures is that part which constitutes what we term the permanent safety marking. It is formed using self-hardening, resin-base paints, and may contain coloring pigments, as well as other ingredients, eg., autocol'limating units, where special .properties as imparted by the ingredients are desired.

The temporary or passing portion of our marking structures is formed from material which is at least semitransparent, and which almost.immediately upon application becomes sufficiently tough and wear-resistant so as to withstand traffic abrasion andthe like for at leas-ta few hours wi-thout being destroyed or otherwise failing, yet is readily removed, as by water washing, without creating any traic hazard or nuisance.

In the drawings made a part hereof,the structure of .street markings of our invention is graphically illustrated.

lvFIGURE 1 is a plan view. of a street marked with a center line.

FIGURE 2 is an enlarged cross section through line 2-2 of FIGURE l.

FIGURE 3 is an enlarged cross sectional-viewof a safety marking structure, formed according to our invention, containing `autocollimating elements.v

Referring to FIGURES l and 2, the structures illustra-ted comprise a'street surface 10, a permanent safety marking or paint layer 4411, and a protect-ive layer 12. In FIGURE 3 the same respective components are correspondingly numbered forV the structure'illustrated. Additionally, autocoliimating elements v13, e.g., small glass reflex light-reecting spheres or beads (see Heltzer Patent 2,574,971) are shown embedded withinrthe pigmented, permanent marking layer 11. As described in the aforenoted Heltzer patent, these autocollimating elements will become operative to direct light back in a cone toward its source after paint on the -topV surface thereof is worn :away by traic Iabrasion. As an alternative, these autocollimating elements may be` pressed into layer 11 (see p Shuger Patent 2,268,537). Other components, of course,

may be inclu-ded in thepermanent safety markings formed f according to-our invention, the structurein FIGURE-3 beingmerely illustrative. l

In forming safety markings rapidly and in the manner contemplated bythis invention, a, self-hardeningresinbase paint is applied in liquid condition to a previously cleaned road surface in a line or other marking,v as desired, and thereafter while the paint` is still in an unset `or unhardenedcondition, i.e., before it has hardened to the point where it is non-tacky and can withstand traic without becoming smeared and dirty, a coating of urea is The urea is applied from a hot, fluid melt and quickly cools and solidies'to form "a protective skin over the applied paint strip, protecting While theproblem of providing durable safety mario" ings in an economical lmanner and so. as not to. inter-,

the paint during the time it requires for hardening to a non-tacky, vdurable state. Within seconds after the urea has been' applied as a protective layer, traffic may pass over the safetymarking structure without causing the paint marking tobecome'dirty or smeared.

The resin-base-paint which forrns the: durable, wearvresistant, permanentsafety markings of ourv structures must be of the type which does not require exposure to air to harden or 'set' to a non-tackyisolid, durablecondition. taining volatile solvents are unsuitable as a class to employ inthe practieefofithis invention. When coated overv ammi Thus',``conventional drying oil Ybase paints "conwith urea, these drying oil paints containing solvents are sealed from the air and remain unset or unhardened for so long a time as the seal is maintained. For the practice of this invention, preferred paints to employ are those which are self-curing, i.e., autogenously curable, into hard but exible, tough, non-tacky iilms, without the necessity for exposure `to air, or the necessity for evaporation of solvent from their mixture. Suitable paints to employ in the practice of our method, although less desired than the 828. This resin is a liquid epoxy resin having an average of more than one 1,2 epoxy group in the molecule. Typical epoxy resins of this type may be produced by the reaction of 2,2-bis(ll-hydroxyphenyl) propane (i.e., Bisphenol A) and epichlorhydrin in alkaline media at elevated temperatures within the approximate range of about 50-150" C. While the resins are complex mixtures rather than ,a single chemical compound, they may be represented by the illustrative formula self-curing resin-base paints, are those formed from Where n has an average value between zero and about 7,

thermoplastic resins. Such thermoplastic resin-base paints contain little or no volatile solvent. After being applied inthe molten state, they slowlyl cool, and thereby harden toa non-tacky, durable state after aperiod of time, usur-y `stance urea possesses a surprisingly excellent group of properties for use. It melts at about 132 C., wellabove -the maximum ambient temperature where street markings are applied, and is easily held inuid condition by raising it to about 150 C. for practical operations as herein discussed. Preferably it is not raised above about 160 C., at which'temperature substantial decomposition -of the urea is in evidence and odors may become obiectionable. Experience has shown that, under varied temperature conditions, urea does not enter into reaction with a wide variety of suitable resin-base paints for use in the practice of our invention. It is easily applied as a hot fluid melt over flowable, unset resin-base paint markings, does not smear the paint markings, and rapidly cools to form a hard, tough, traine-sustaining layer over the markings. The hardened crystalline urea layer stands up for a suicient time under the flow of traic so as to protect the resin-base paint markings from contact with trafc during the time needed for their hardening to a tough, abrasion-resistant and wear-resistant solid state. Further, the cooled and solid urea layer is semi-transparent and colorless so that the 4color of the marking is not obscured during the time it is weak and needs protection.

Of practical importance is the fact that urea layers are readily removed from a ymarking after their protective function is no longer needed, i.e., after the paint markings have hardened to a non-tacky, traffic-resistant state. The removal of the urea layer creates no problem. Rain falling on it will dissolve the urea and wash it away. If desired, onemay remove it by street washing. The paint markings remain as clean-and brightly colored indicia.

vAs an additional advantageous property of applied urea layers may be cited the fact that they are odorless and are not offensive to the public; During the time ofthe layers protective function vas well as during 4its removal by Water washing, no vrtrailic hazard such'as slipperiness is .createdj YThe following examples are` offered to illustrate the Ateachings herein, butare not -to be construed as limitative of this invention. Unless otherwise noted, all parts are byweight.

Theepoxy resin was obtained commercially from Vthe ShelLDevelopmentCompany underthe trade name Epen depending for the most part on the relative proportions of Bisphenol A and epichlorhydrin in the initial reaction mixture, the larger amounts of epichlorhyd'rin being used to prepare liquid epoxy resins. .Other polyhydric phenols, e.g. 'resorcinoh 2,2-bis-(4-hydroxyphenyl)-butane, and various tris-phenols, may be substituted for the Bisphenol A. Various other polyhydroxy compounds may likewise be substituted, by appropriate known procedures, for the polyhydric phenols in preparing analogous resinyous base materials, ethylene glycol and glycerine being typical examples. Epen 828 is but one illustrative suitable liquid epoxy resin (melting at about 8 to 12 C). It has a Gardner-Holt viscosity at 25 C. of Z5 to Z6,

' and an epoxide equivalence of about 190 to 210. In other application.

words, about 190 to 210 grams of this resin contain 1 gram equivalent of epoxide.

The polyamid resin of the above formula reacts with the epoxy resin to promote hardening of the composition, and is the addition product of polymerized long 'chain fatty acids and polyfunctional primary and secondary amines. Versamid is 'stated by the manufacturer, ,General Mills. Inc., to have an average molecular weight of about 2,000, an acid number of 7, and a Brookfield viscosity of about 45,000 to 55,000 centipoises at 23 4C.

Methyl amyl acrylate monomers may be prepared by ester reaction between acrylic acid and methyl 'a'rnyl alcohol (methyl isobutyl carbinol).

About 1100 parts of Mixture A and 43.3 parts of Mixture B, together with 14 parts additional of methyl amyl acrylate monomers, and 5 parts of diethylene triamine curing agent for the epoxy resin, were blended together by stirring, and then sprayed onto a concrete road surstripes or lines formed using one gallon of paint. The

large quantity of urea employed served to cover all areas of the paintedV stripes as a layer even though molt-en'urea shows some tendency, when attempts are made to apply it as an` extremely thin layer, Ito crawl oit the painted stripes. Within about 30 seconds after the molten urea was applied, it had hardened suiciently to provide a protective layer completely covering the painted markings. Vehicles were drivenover thernarkings, without damage tothe same, the urea layer serving to protect the markingsjfrom traic contact.

After about 8 hours of protection, the painted markings of this example had cured suiliciently so that the urea could be removed leaving a permanent durable and non-smudged safety marking. Removal of th'eurea was accomplished by rain, which fell about' 8 hours after The rain water dissolved the urea and washed it away.V No traic hazard or public nuisance was created.

Using the compositions of this example, theY foregoing View method was employed to mark asphalt and cobblestone p street surfaces, and gave the desired results as afore- EXAMPLE 2 Parts Epoxy resin (Epon l004) :6 Dibutyl phthalate plasticizer 6.7 Pigment grade calcium carbonate (Atomite) 18 Pigment grade titanium dioxide (Unitan OR150) l2 v Small glass beads having a diameter of about 2.5

to 7 mils and a refractive index of about 1.5 47.7

The epoxy resin of this example, while formed using materials such as set forth in Example 1, was formed 'with less epichlorhydrin in the reaction mixture so as to produce a resin which remains as a solid at room temperature. .Epon 1004 melts at about 95-105 C., and has an epoxide equivalency from about 870 to 1025.

All the ingredients above, including the beads, were mixed together by kneading action at a temperatureof 175 F. until a uniform smooth blend containing the glass beads was formed. The blend was poured into pails and allowed to cool.

To about 17 parts of the above batch was addedabout one part of phthalic anhydride, which serves as a curing or hardening accelerator for the composition. This mixture was then melted by heating to about 220 F., and the phthalic anhydride blended therein. While hot','the mixture was knife coated on a concrete roadway in the form of safety marking lines. was used to form stripes totalling about 40 square f eet in' surface area. The applied paint cooled rapidly and solidified on cooling to a tacky, semi-solid state. Hot molten urea was ilute sprayed immediately over the markings in a sufficient amount to form a thin urea layer covering the total area of the markings except for a short strip which was left free of urea. About one minute after the urea was applied, traiic was allowed to pass over all areas of the marking strips, both those covered with urea and those left uncovered. Traiiic over the strip free of urea caused it to be smeared and to pick up dirt, whereas the urea protected 'markings were left free of smearing and dirt. After about one hour the urea layer could be removed by water washing without the underlying paint film becoming smeared or dirty as a result of subsequent trailic contact.

While the paint of this example, evenv with added anhydride, requires several Weeks to cure at room ternperature, its surface stickiness is substantially killed by the hot melt applicationof urea thereover, which serves yto heat the exposed and urea contacted surface areas of the paint film and accelerate curing of such surface areas,

thus providing a thin essentially non-tacky skin of cured paint over the underlying portion of paint which takes longer to cure. Shortly after the urea has been applied to this paint film, therefore, its protective function is no longer needed and it may be removed.

EXAMPLES The composition and procedureof Example l lwere employed except that 14 parts (of methyl ethyl ketone solvent were substituted for the 14 parts of additional methyl amyl acrylate monomers in the paint formula. The methyl ethyl ketone in this formulation does-not enter into reaction with the other components of the paint formula (as happens in the formula of Example 1), and is entrapped in :the finally cured paint mmkings as a volatile solvent. Despite this fact, the marking One gallon of the mix As in the predure employed in Example 1, the paintv of this example was applied in stripes on a road surface-in this case an asphalt surface-and coated over with a layer of urea. lSubsequently the urea was washed away after the underlying paint lm was cured.

EXAMPLE 4 The composition and procedure of Example 1 were used except that styrene oxide monomers were substituted on .a weight for weight basis for all of the methylamyl -acrylate monomers of Example 1. Styrene Oxide, like methyl amyl acrylate, serves as a reactive diluent in this composition, entering into reaction (an addition reaction as .distinguished from acondensation reaction) with 'other components of the paint mix during hardening, and becoming an integral part yof the resulting marking. In all respects this composition performed as illustrated for the markings of Example 1. Hot melted urea was used as a top coat, as described in Example 1.

EXAMPLE 5 The following paint formulation illustrates the use of a method of this invention with self-hardening resin-base paints which may be characterized as thermoplastic paint mixtures: l

Glass beads of the character described in Example 2 168 The alkyd resin was an oil-modified glycerol phthal-ate prepared from a mixture of at least 31% phthalic anhydride by weight and about 57% soya oil with the remainder being essentially glycerol. This resin has a. Gardner- Holt viscosity of I to L, and an acid number between 6 and 14.

The titanium dioxide pigment here employed was a calcium modified pigment formed by precipitating titanium dioxide onto finely divided calcium sulfate, and consists of about calcium sulfate as the core of pigment particles, with about 30% titanium dioxide occupying surface areas of the particles. This pigment is 'merely illustrative of one type to employ. Many others are suitable.

The paint formulation of the example was maintained in a hot fluid condition by heating it to a 275 F. for application to roadways. It was knife coated in stripes on -a concrete roadway; and immediately after applica-y tion, hot molten urea was poured upon it. The urea cooled to form a protective layer within about one minute after application, and traffic was allowed to pass over the marking. No damage to the marking occurred. After about one hour, which is a sufficiently lengthy period. of

time for this paint film to loSe its tack and harden into a solid durable film, the urea could be removed, e.g., by

v spraying water over the structure, andthe markings were be employed as the base for paint formulations useful the 'practice of this invention. #Curing agents of a wide variety, as welll understood in the self-curing resinfart,

may be useful. Pigments may vary. While white has become a popular marking pigment, as illustrated in the examples, yellow lead chromate is frequently employed. Many others, however, will be found to function equally as well in the practice of the invention.

The foregoing is intended to illustrate but not limit our invention, and all equivalents are fully comprehended.

That which is claimed is:

l. The method of providing clean, sharply outlined, traffic-resistant markings on trailic-way surfaces with no more than momentary interruption of trafiic over said surfaces, comprising applying to a desired area of the surface a thin coating of a self-hardening spreadable liquid resin-base paint marking composition, applying thereover as a melt a continuous layer of hard, brittle, water-soluble crystalline urea material melting at a temperature well above the maximum ambient temperature and below the temperature at which degradation of the niark-ing composition is obtained, said crystalline material being applied Vin .a continuous layer over said marking composition before said marking composition has hardened sufficiently to sustain trafc and permitting the melt to solidify.

2. The method of claim l in which the marking cornposition is rapidly heat-curing and at least the surface of the thin coating is accelerated in curing during contact with the applied molten crystalline material.

3. The method of claim 1 in which the marking composition is thermoplastic and hardens and slowly loses surface tackiness on cooling from plastic condition.

4t A method for providing durable, Wear-resistant, clean, visual, safety markings on traiiioways in such manner as not ,to interfere more than momentarily with the flow of traic thereove'r, said method including the step of applying a layer of urea over a selffhardening resin-base paint marking substantially immediately after said marking has been applied `from Huid composition to saidrtraiiic-way, said urea ybeing applied over said marking as a hot, melted-huid whichcools rapidly upon application to form a temporary, trame-sustaining, easilyremoved, non-hazardous, water-soluble, protective layer over said marking, thereby to protect said marking from dirt and traffic contact during the time required by said marking to set to a durable, tradire-resistant state.

5. A method of applying durable, wear-resistant, clean, visual, safety markings on traic-Ways in such manner as not to interfere more than momentarily with the llow of traffic thereover, vsaid method comprising applying upon the surface of a traffic-way a safety marking of a pigmented, self-hardening, resin-base paint, and applying urea as a layer over said marking substantially immediately after forming said marking, said urea being applied over said marking from a hot,'uid melt which cools rapidly upon application to form ya temporary, traflicsustaining, easily-removed, non-hazardous, water-soluble, protective layer over said marking, thereby to protect said marking from trafc Contact during the time required by said marking to harden to a durable, trahie-resistant state.

6. On a traffic-way: traic markings of self-hardening resin-base paint composition temporarily protected by a hardened continuous transparent protective surface layer of ure-a, said urea being non-reactive with said self-hardening composition. i

7. A structure comprising a hard surfaced traffic-way, a layer of pigmented, non-tacky, self-hardenable, tough, exible and durable, resin-base paint von said traiicway, and a temporary protective, traffic-sustaining layer of cool and hardened urea over said paint on said trahie-way, said urea layer being non-reactive with said paint on said traffic-way and being easily dissolved by water andk washed away from said structure without creating trallc hazards and offensive odors.

References Cited in the tile of this patent UNITED STATES PATENTS

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