GB2087404A - Road marking materials - Google Patents

Abstract

The invention resides in a thermoplastic road-marking material which comprises a flowable particulate mix of resin, extender, pigment, aggregate and plasticiser in suitable overall proportions. At least some of the resin, extender and plasticiser are in combination as pellets. The ratio of resin to extender in the pellets is up to about 3:1. The overall proportions in the pellets are 70% by weight resin, 22% by weight extender and 8% by weight plasticiser. The material has overall plasticiser content from 1.5 to 3.5% by weight, a pellet content from 10 to 25% by weight and a free plasticiser content of up to 2% by weight, preferably between 1/2 and 11/2 % by weight. The free plasticiser helps to retain the fines in the mix, even in wind.

Description

SPECIFICATION Road marking materials The invention concerns improvements in and relating to the manufacture of thermoplastic roadmarking materials.

Basically, in this country, such materials for hot-application as a liquid that subsequently set are made to British Standard BS 3262 and comprise light-coloured aggregate, pigment and extender, bounded together with a thermoplastic resin plasticised as required. Glass beads of suitable grading can be incorporated to improve reflectivity. Requirements, or what is acceptable, in or for other countries may vary but such variations conveniently represent the boundaries for constituents of materials of this invention.

Usually, such materials have been made in batches as a hot liquid mix that is subsequently cooled to a solid mass, say in drum-like containers therefor. In developing an unmelted flowable particulate mix for such materials as supplied to site for heating and hot liquid application by screeding or spraying, we have encountered certain problems especially when using liquid plasticisers. In particular, we have sought to avoid the disadvantages of pre-mixing only the dry components and then admixing the plasticiser on site. To that end, we have discovered that liquid plasticiser can be dispersed through the other, already-mixed, constituents in a dispersion stage using rotating blades, conveniently a central stack of substantially flat blades rotating at 1 50-1 50 r.p.m., preferable about 200 r.p.m.

At relatively low levels of liquid plasticiser content (up to 2% preferably 11%) the final mix is entirely satisfactory in that liquid plasticiser inhibits loss of lightest constituents in windy conditions and in that the final mix is still particulate and flowable with no significant tendency to compact, coagulate of otherwise stick together during storage.

However, if the final mix has a higher level of dispersed liquid plasticiser content (particularly at and above 2 2%) we find a tendency to compact and lose particulate flowability after storage for some time. Also, for such plasticiser levels, the inevitable heating action of the dispersion blades leads to difficulties in the dispersion stage by constituents of the mix sticking together or to the dispersion vessel. It would, of course, be possible to avoid such problems by using a solid plasticiser as available in wax pill form, but such is considered to be not commercially viable here at present as it is comparatively expensive.

Screed-applied road marking materials usually require lower plasticiser contents than those for spray application, but, even so, often have about 2.5% plasticiser rising to 33 2% for materials to be sprayed. The above-mentioned problems are thus relevant both to spray applied and screed applied road marking materials in providing particulate mixes therefor.

In order to overcome such problems, what we now propose is that constituents of the desired end product, including at least some resin and liquid plasticiser, be pelletised, preferably by a process involving liquefaction of such resin component by heating followed by cooling of metered quantities thereof to form solid blobs, beads or pastilles as the desired pellets, We have used such pellets of a size comparable to that of resin alone, and have considered that to be advantageous in respect of utilising the benefits of past experience, especially where other or balance constituents are to be mixed therewith as mentioned below.However, we believe that any size and form of pellet, say flakes, can be used so long as it is effective to achieve ready flowability, which could be hindered if they were so small as to present a gross surface high enough for any later-added liquid plasticiser to cause coagulation. A size above 4 cm2 in section is preferred, conveniently below 2 cm2.

If the entire content of our material were to be pelletised, wear problems could well arise in the feed and metering parts of pelletisation equipment due to the presence of abrasive constituents such as sand of the aggregate. Thus, we propose that peileted constituents shall exclude at least aggregates to aid in reducing wear in pelletisation equipment, and also pigment to facilitate making different coloured products. Also, of course, some liquid plasticiser will normally be added at or after mixing of the pellets in order to achieve the above-mentioned advantages of an end-product that is particulate, flowable, end not particularly susceptible to compaction, but yet does not suffer unduly from blowing away of fine constituents in windy site conditions.

Further development, study and consideration has led us to propose a standard pelletisation formulation mixture that will be suitable for a range of screeding and sprayable materials, rather than to produce individual pellet formulae (one for each desired end product), thereby avoiding consequent expense and risk of confusion.Our investigations reveal that, at least over a range of from about 1 2 / to about 3 2% plasticiser content by weight, and accompanied by appropriate variation of pellet content in the tinal mix, a viable standardised pellet formulation results if it includes sufficient plasticiser to reduce that plasticiser added free to the final mix to be of the order of 121% for the highest plasticiser mix, and excludes sufficient plasticiser to allow plasticiser to be added free to the final mix of plasticiser to be of the order of 21% even for the lowest plasticiser mix.

However, we have noted during mixing a tendency for the pellets to be or to become somewhat tacky, as would be expected compared with resin alone due to their oil content, and it is possible for substantially all of the very fine constituents to adhere reasonably firmly to the pellets without admixture of liquid plasticiser. A range of O to 2% is thus given herein for dispersed "free ' liquid plasticiser.

Resin content of the final mix also varies over the range of desired products so that a balance of resin will normally be required in addition to standard pellets. Where, as is usual, the minimum plasticiser final mix also has the lowest resin content of that resin range, the standard pellet can provide all of the resin requirements and leave a minimum balance of plasticiser to be added at final mixing in order to avoid free powder or other light particles in that minimum plasticiser product.

However, such a pellet could place rather critical quality requirements on available materials, lead to controlling addition of only small quantities of resin for next higher resin final mixes, and represents a maximum cost item as resin is itself high in cost. The latter can be a significant consideration where pelletisation is not done "in-house", i.e. contracted to a supplier. We therefore prefer to use a somewhat lower resin content for the pellet formulation and thereby improve formulation flexibility and ease of subsequent manufacture as well as prescribe a lower value item.

The resin-to-plasticiser ratio can be between 40 and 45% higher than required in the final mix (usually between 6:1 and 7:1, preferably below 6.5:1).

Normally spray-applied materials will have resin content of about 1 8 to 20% and screed-applied materials can have a lower resin content say 1 5 to 16% Low viscosity resins, e.g. can reduce these resin contents to as low as 1 5 to 16% and 11 to 12% respectively.

It will be appreciated that the main function of the additional plasticiser is to avoid the presence of dry powder. Also, a standard pellet will have to serve for different colours of final product, e.g. white and yellow, and pigment will normally be of light dry powder form, say titanium dioxide for white. It is particularly important that such pigment is not lost at site. Thus, the added plasticiser is helped to secure that if at least some of fine grade extender, say amorphous calcium carbonate available as "whiting", is incorporated into the pellet formulation. We have found it to be satisfactory to have a ratio of up to about 3 :1 for resin and extender content of the pellets.

One example is now given of a specific pellet material formulation suitable for a range of final mixes having between 1 121% and 321% oil content.

EXAMPLE A Resin 70.0% Plasticiser 8.0% Extender 22.0% Whiting (Ca CO3) Where, as is usual, small quantities of a wetting agent, such as stearic acid, are included, it has been found to be most convenient if that is incorporated, preferably in whole, into the pellet formulation.

The following three examples give details of both of overall constituent percentages and actual mixes including pellets.

EXAMPLE B Overall % Pellets (3.75%) Additional Resin 12 2.625 9.375 Extender-amorphous 9.2 0.825 8.375 CaCO3 (Whiting) Pigment (Ti 02) 10.0 10.0 Aggregate Sand 24 24 Crystalline CaCO3 33 33 Glass beads 10 10 Plasticiser Oil 1.8 0.3 1.5 EXAMPLE C Overall % Pellets (11.25%) Additional Resin 15.0 7.875 7.125 Extender 16.0 2.475 13.525 (Whiting) Pigment (Ti 02) 6.0 6.0 Aggregate Sand 27.0 27.0 Crystalline CaCO3 13.6 13.6 Glass beads 20.0 20.0 Plasticiser Oil 2.4 0.9 1.5 EXAMPLE D Overall % Pellets (21.25%) Additional Resin 20 14.875 5.125 Extender (Whiting) 7.8 4.675 3.125 Pigment (Ti 02) 10 10 Aggregate Sand 33 33 Crystalline CaCO3 1 6 16 - Glass beads 10 10 Plasticiser Oil 3.2 1.7 1.5 It will be noted that Examples B, C and D are predicated upon adding a standard 1.5% free plasticiser oil for dispersion through the other constituents of the mix. That is considered advantageous in always having the same oil dispersion and thus operational desiderata for the preferred dispersion stage of our cofiled application. That leads to pellet contents 3.75 to 21.25%.

It will, however, be appreciated that there is considerable possible flexibility for pellet content, for example maximising pellet content by reducing the later-added oil in the dispersion stage to levels lower than 1.5%, say to 21% which, for Example B, would increase pellet content to 16.25%. A similar pellet content for Example C would increase the dispersed oil content only to 1.9%, i.e. below our preferred safe maximum of 2%. Thus, the pellet composition of Example A is capable, if desired, of permitting a substantially constant pellet content for materials over a range represented by Examples B to D.

Nonetheless, however, we believe that there are desirable production advantages to be gained from working the dispersion stage with substantially the same proportion of oil addition.

The above is believed to demonstrate (in relation to Examples B, C and D which are all for white reflective material) that overall material formulations with oil contents in a range of about 1 2% to 3 2% can have a pellet content within the range 10% to 25% for additional oil of between 1% and 1 2% (which is highly satisfactory for fines retention, even in wind, and particulate flowability that will not deteriorate with storage under reasonable conditions, such as in a site storage hut).

Claims (20)

1. A thermoplastic road-marking material comprising a flowable particulate mix of resin, extender, pigment, aggregate and plasticiser in suitable overall proportions, wherein at least some of the resin, extenter and plasticiser are in combination as pellets.

2. A material as claimed in claim 1 , wherein the mix has up to 2% by weight of free plasticiser.

3. A material as claimed in claim 1 or 2, wherein the mix has at least 31% by weight of free plasticiser.

4. A material as claimed in claim 1 or 2, wherein the mix has approximately 1.5% by weight of free plasticiser.

5. A material as claimed in claim 1 , wherein the mix has no free plasticiser.

6. A material as claimed in claim 4, wherein the overall pellet content in the mix is from 3.75 to 21.25% by weight.

7. A material as claimed in claim 3, wherein the overall pellet content in the mix is 16.25 to 33.75% by weight.

8. A material as claimed in any one of the preceding claims wherein the ratio of resin to extender in the pellets is up to about 3:1.

9. A material as claimed in claim 8, wherein the overall proportions in the pellets are 70% by weight resin, 22% by weight extender and 8% by weight plasticiser.

10. A material as claimed in any one of the preceding claims wherein the overall proportions in the mix are resin from 10 to 20% by weight, extender from 7.8 to 16% by weight, pigment from 6 to 10% by weight, aggregate from 59 to 67% by weight and plasticiser from 1.5 to 3.5% by weight.

1 A material as claimed in claim 10, wherein the resin-to-piasticiser ratio in the mix is from 6:1 to 7:1.

12. A material as claimed in claim 1 wherein the resin-to-plasticiser ratio in the mix is below 6.5:1.

1 3. A material as claimed in claim 10, 11 or 12, wherein for spray application the proportion of resin in the mix is from 1 8 to 20% by weight.

14. A material as claimed in claim 10, 11 or 12, wherein for screed application the proportion of resin in the mix is from 15% to 16% by weight.

1 5. A material as claimed in claim 10, 11 or 12, wherein for spray application the proportion of resin in the mix is from 15 to 16% by weight for low viscosity resins.

16. A material as claimed in claim 10, 11 or 12, wherein for screed application the proportion of resin in the mix is from 11 to 12% by weight for low viscosity resins.

1 7. A material substantially as herein described with reference to and as illustrated in the accompanying Examples.

18. A pellet comprising a solidified melt of resin, extender and plasticiser as a component of or for a thermoplastic road-marking material as claimed in any one of claims 1 to 16.

19. A pellet as claimed in claim 18 wherein the ratio of resin to extender is up to about 3 :1.

20. A pellet substantially as herein described with reference to and as illustrated in Example A.