US 3355311 A
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1967 K. R. GOSSELINK 3,355,311
REFLECTIVE COATINGS Filed Oct. 22, 1963 LAYER OF TRANSPARENT REFLECTIVE BEADS BINDER COATING OF A POLYMER OF AN ALKYL METHACRYLATE.
SUBSTRATE OF METAL, wooo, on THE LIKE INVENTOR. K421 2. 6055452 //W( United States Patent 3,355,311 REFLECTIVE COATINGS Karl R. Gosselink, Rocky River, Ohio, assignor to Pittsburgh Plate Glass Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 22, 1963, Ser. No. 317,881 2 Claims. (Cl. 11733) This invention relates to surfaces having thereon coatings for the reflex reflection of light, and more particularly, an improved type of coating for such surfaces comprising a thermoplastic alkyl methacrylate polymer as a binder for transparent reflective beads.
Reflective surfaces are used for many purposes. For example, they are extensively employed in signs, for highway markings, as projection screens, and in similar applications wherein increased reflectance and brightness are desired. This invention provides a new and improved type of reflective surface for these and similar purposes.
The reflective surfaces of this invention are made up of a substrate, a layer of binder coating comprising a thermoplastic polymer of an .alkyl methacrylate adherently bonded to the substrate, and a layer of small, transparent, reflective beads attached to the binder coating.
The accompanying drawing is Ka schematic diagram illustrating a magnified cross-section of these reflective surfaces. As shown, the layer of reflective beads is of single-bead thickness; however, surfaces in which all or part of the bead layer is several beads thick are also within the invention. Similarly, the thickness of the binder layer can be varied substantially, in some instances suflicient to entirely cover the beads, as when the surface is to be subjected to abrasion which will result in exposure of the beads. Also, beads can be attached to the surface of a thick layer of binder by partially drying and/or heating the binder layer.
The substrate may be of any shape and can be made of any suitable material designed for the end use to which the reflective surface is to be put. Thus, for various applications the substrate can be glass, wood, metal, masonry, paper, leather, or the like, or it can be a natural or synthetic fiber or resin, or similar material. In some instances, it is desirable to employ a primer or base coating on the substrate in order to improve the adhesion of the binder coating thereto.
The binder coating is made up of a polymer of an alkyl methacrylate. It is preferred that at least a part of the polymer be methyl methacrylate, although other methacrylates, generally having up to about 15 carbon atoms in the alkyl group, can also be employed. Such alkyl methacrylates include ethyl methacrylate, propyl methacrylate, butyl methacrylate, isooctyl methacrylate, decyl methacrylate, lauryl methacrylate, and the like.
The alkyl methacrylate polymer can be a homopolymer, in which case polymethyl methacrylate is preferred. There may also be employed copolymers and interpolymers of various alkyl methacrylates. Especially useful copolymers are those in which methyl methacrylate is copolymerized with about 5 to about 25 percent of another alkyl methacrylate, such as those mentioned above, and particularly .alkyl methacrylates having at least 8 (generally up to about 15) carbon atoms in the alkyl group. There may also be employed copolymers and interpolymers containing one or more alkyl methacrylates along with minor amounts of other monomers copolymerizable with the alkyl methacrylate in which the properties of the polymer are substantially similar to the properties of the polymers described above. Alkyl acrylates, usually of 4 to 12 carbon atoms, are especially contemplated as comonomers; one example of a desirable polymer contains 80 percent methyl methacrylate and 2.0 percent ethyl acrylate. All of these materials areincluded within Patented Nov. 28, 1967 the scope of the term polymer of alkyl methacrylate as used herein.
The binder coating may include pigments or coloring agents in order to provide a colored reflective surface or a surface of a particular design, as for a sign or marking. Conventional pigments of the type employed with methacrylate polymer coating compositions can be used for this purpose.
The use of these methacrylate polymers as binder coatings in the reflective surfaces described herein provides many of their improved properties. For example, improved adhesion of the reflective beads to the binder coating is attained and better optical properties in the finished coating are provided.
Attached to the binder coating is a layer of transparent, reflective beads, spherical or lenticular in shape. The size of the beads can be varied widely, but is usually in the range of from about 1 to about 40 mils in diameter. The beads may be glass, in which case it is desirable to employ beads having a diameter of about 1 to about 20 mils. The preferred reflective coatings employ beads made of a methacrylate polymer as described below; in these instances the beads are suitably somewhat larger, e.g., from about 5 to about 40 mils in diameter.
As indicated above, glass beads or beads of .any other transparent reflective material can be employed. It is preferred, however, to utilize beads made of a polymer of an alkyl methacrylate, such as beads made of homopolymers or copolymers of methyl methacrylate of the type described above. It is especially preferred to employ beads having the same or similar composition as the polymer used as the binder coating. The use of beads of an alkyl methacrylate polymer provides additional advantages in the reflective surfaces made therefrom, such as markedly improved abrasion resistance and, when employed with a suitably colored'substrate and/or binder coating, increased fluorescence and deepening of the color along with greatly increased sparkle.
The binder coating is ordinarily applied to the substrate as a solution in an organic solvent or as an emulsion in water. The reflective beads are in most cases applied to the binder prior to evaporation of the solvent. Alternatively, the binder coating can be dried and then the reflective beads applied later by heating the binder to permit adhesion of the beads.
It may be noted that it is possible to utilize a bead polymer as the binder polymer by dissolving the beads in a suitable solvent. For example, when, as is preferred, the same polymeric composition is to be employed in the beads and as the binder, the alkyl methacrylate composition can be head polymerized and part of the beads dissolved in a solvent and applied as the binder coating,
along with any desired pigments and the like.
The methacrylate polymers employed as the binder coating are produced by any of the well-known techniques utilized in making methacrylate polymers for use in coatings. Emulsion polymerization, solution polymerization or suspension polymerization can be employed. For example, solution polymerization is carried out by refluxing the monomer or monomers in a solvent or mixture of solvents along with a catalyst and, if desired, a chain transfer agent, wetting agent or other materials until the polymerization takes place to the desired extent. In emulsion polymerization, the monomers, catalyst and any other materials are admixed with water with vigorous agitation, the mixture being heated to a temperature of about I C. to about C. After the reaction has taken place, which generally requires about an hour, the mixture is cooled and the latex is precipitated by the addition of an alcohol which is at least partially soluble in water, such as methanol, ethanol or isopropanol, or an acid such as hydrochloric acid, or the like.
Beads of a polymer of an alkyl methacrylate suitable for use as the transparent reflective beads herein are produced by carrying out the polymerization in suspension. This type of polymerization may be considered as a bulk polymerization and is carried out ordinarily by admixing a solution of the monomer or monomers, the catalyst and a chain transfer agent with a water solution containing a protective colloid and an aqueous buffer. Suitable protective colloids include polyvinyl alcohol, alkali metal salts of polyacrylates, such as sodium polyacrylate, polyacrylamide, bentonite, starch, acetylated starch, magnesium silicate, and the like. The buffer employed is typically a phosphate, such as a mixture of monosodium phosphate and disodium phosphate. The reaction is carried out by admixing these solutions with rapid agitation while heating the mixture to a temperature of about 70 C. to about 95 C., generally for about 1% to 3 hours. The beads are readily recovered by cooling the mixture and filtering through paper, glass, cloth, fine silk cloth, or the like.
The above polymerizations are in most cases carried out with a peroxygen type catalyst, such as acetyl benzoyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, dieumenyl peroxide, tertiary butyl hydroperoxide, benzoyl peroxide, peracetic acid, tertiary perphthalic acid, ammonium persulfate, and the like. Azo compounds, such as azo-bisisobutyronitrile and para-methoxyphenyl diazo-thio(2-naphthyl)-ether, are also useful as polymerization catalysts. While the quantity of catalyst can be varied considerably in most instances, it is conventional to employ from about 0.2 percent to 2.0 percent of catalyst based upon the weight of the monomers.
In producing the polymers above, it is often desirable to include a chain transfer agent or a chain modifying agent in the polymerization mixture. For this purpose, mercaptans such as dodecyl mercaptan, octyl mercaptan and tertiary dodecyl mercaptan are often utilized, although other materials such as carbon tetrachloride, allyl acetate, allyl carbamate, acetic acid, and the like can be used for similar purposes. When a chain transfer agent is included, about 0.1 percent to about 2.0 percent by weight based on the amount of monomer present is ordinarily utilized.
If desired, the beads of the methacrylate polymer described above can be colored by the addition of suitable pigment materials and/ or dyes.
Set forth below are several examples illustrating the manner of producing the polymers of alkyl methacrylates usable as binder coatings herein. All parts and percentages are by weight unless otherwise specified, as is the case throughout this specification.
BINDER POLMER A A solution copolyrner of methyl methacrylate and lauryl methacrylate was prepared by refluxing a mixture of 700 parts of toluene, 300 parts of acetone, 900 parts of methyl methacrylate, 100 parts of lauryl methacrylate, and parts of benzoyl peroxide, Refluxing was carried out for 4 hours at a temperature in the range of about 77 C. to 81 C., after which another 500 parts of toluene were added and reflux continued for 3 hours at about 81 C. A further addition of 1000 parts of toluene was made, after which 640 parts of solvent were distilled off at a maximum temperature of 110 C. The resulting polymer solution had a solids content of 35.4 percent and a Gardner-Holdt viscosity of U+. The relative viscosity of the solution was 1.208, which corresponds to a molecular weight of approximately 112,000.
BINDER POLYMER B A mixture of 700 parts of toluene, 300 parts of acetone, 680 parts of methyl methacrylate, 300 parts of lauryl methacrylate, 20 parts of methacrylic acid, and 5 parts of benzoyl peroxide was refluxed for a total of 8 hours at a temperature between 75 C. and 805 C. After 12 hours and again after 4 hours, 1.25 parts of benzoyl peroxide and 12 parts of toluene were added to the refluxing mixture. At the end of the reflux period, 450 parts of acetone were added and the reaction mixture cooled. The solution obtained had a solids content of 37.8 percent, a Gardner-Holdt viscosity of F-, a relative viscosity of 1.170, and an acid value of 7.0.
BINDER POLYMER C A homopolymer of methyl methacrylate was produced by the procedure employed in making binder polymer A above, except that 1000 parts of methyl methacrylate were used in place of the methyl methacrylate-lauryl methacrylate mixture therein.
In addition to the alkyl methacrylate polymers as illustrated above, the binder coating may include pigments, plasticizers and similar additives. It has been found desirable in many instances to also include minor amounts of epoxy resins, vinyl halide resins, or similar resinous materials. These are used, for example, to improve the adhesion of the binder coating to the substrate.
A bead polymer suitable for use as the reflective beads in the herein-described coatings was prepared as follows:
BEAD POLYMER D A mixture of 1495 parts of water and 5 parts of an acetylated starch (Kofilm No. 50) was heated with agitation to C. until an almost clear solution was obtained. Fifty (50) parts of buffer solution (prepared by admixing 1 part sodium dihydrogen phosphate, 17 parts of disodium hydrogen phosphate and parts of water) was added. To the resulting mixture was added a mixture of 450 parts of methyl methacrylate, 50 parts of lauryl methacrylate, 5 parts of benzoyl peroxide, and 6.25 parts of tertiary dodecyl mercaptan. The resulting polymerization mixture was then heated with agitation at 75 C. to 80 C. for 3 hours, after which the mixture was cooled to 30 C., filtered, washed with water and dried at F. for 16 hours. Clear beads of polymer were obtained. When dissolved to a total solids content of 36 percent in toluene, the polymer solution had a Gardner-Holdt viscosity of S.
Other bead polymers that can be used in the invention described herein were prepared using the procedure employed in making bead polymer D, but substituting the desired monomer or monomers therein. Thus, bead polymer E was produced by homopolymerizing 500 parts of methyl methacrylate. Bead polymer F was produced from 400 parts of methyl methacrylate and 100 parts of octyl methacrylate. Bead polymer G was produced from 450 parts of methyl methacrylate and 50 parts of decyl methacrylate and octyl methacrylate. Bead polymer H was produced from 340 parts of methyl methacrylate, parts of lauryl methacrylate and 10 parts of methacrylic acid. All of these produced transparent reflective beads of suitable size for use in preparing coatings having high reflectance and superior resistance to abrasion.
Several examples of the manner of producing these reflective surfaces are as follows:
Example 1 The following components were blended to form a coating composition:
Parts by weight Binder polymer A (35.4 percent solids) 381.3
Butyl benzyl phthalate (Santicizer M 30.0 I Epoxy resin (reaction product of epichlorohydrin and bisphenol A having an epoxide equivalent of to 200; known as ERL-2774) 5.0 Vinyl halide resin (86 percent vinyl chloride, 13 percent vinyl acetate, 1 percent maleic acid; known as Vinylite VMCH) 21.0 Orange fluorescent pigment (Switzer D14 Fire Orange) 14.4 Titanium dioxide 40.0 Methyl ethyl ketone 144.0 Cellosolve acetate 20.0 Toluene 6.0
Two steel panels were sprayed with a Z-mil film of the above composition and air-dried until the surface is tacky. One of the panels was then sprinkled with a layer of 40 mesh glass beads (about mils maximum diameter). The other panel was similarly coated with a layer of beads corresponding to bead polymer D above, of 30 mesh (about 25 mils) size. Both panels were then baked for minutes at 180 F.
Both panels exhibited desirable reflectance, visibility and optical properties. However, the panel containing the polymer beads showed a deepening of the color and a definite increase in sparkle, providing more visibility under minimum lighting conditions. Similar eflects were noted in panels using up to about 15 percent of the pigment.
In addition, the polymer beaded panel had a markedly greater resistance to abrasion (as tested by a Taber abrasion tester). The Wear was more uniform and less severe, compared to the glass beaded panel which had a loss of surface in spots where the beads were dislodged.
Another important difference in the panels is apparent when they are viewed under black light (for example, from a General Electric EH-4 flood lamp with a filter to absorb most of the visible components). In this instance, the panel with polymer beads exhibits a marked fluorescence, whereas the glass beaded panel is virtually invisible.
Example 2 Panels were prepared as in Example 1, except that the binder coating contained 1.33 parts of a blue-whitener pigment (Tinopal SFG) in place of the orange fluorescent pigment. In this case, the above effects are also noted and, in addition, the glass beads decrease the reflectance and fluorescence, while the polymer beads enhance these properties. This effect is progressive using up to about 8 percent of this pigment, based on the film solids.
In these and other tests it was illustrated that the binder coatings comprising polymers of an alkyl methacrylate of the various types described above provide reflective coatings having highly desirable properties with transparent reflective beads of various types, and particularly so when employed along the beads made of similar alkyl methacrylate polymers.
According to the provisions of the patent statutes, there are described above the invention and what are now considered to be its best embodiments. However, within the scope of the appended claims, it is to be understood that the invention can be practiced otherwise than as specifically described.
1. A reflective surface consisting of a substrate having thereon an adherent layer of a binder coating comprising a thermoplastic polymer of an alkyl methacrylate and attached to said binder coating a layer of small, transparent, reflective beads of a thermoplastic polymer of at least one alkyl methacrylate, said beads having a diameter of from about 5 to about mils, said binder coating and said beads both being of the same thermoplastic polymer.
2. A reflective surface consisting of a substrate having thereon an adherent layer of a binder coating comprising a thermoplastic polymer of methyl methacrylate and attached to said lbinder coating a layer of small, transparent, reflective beads of a thermoplastic polymer of methyl methacrylate, said beads having a diameter of from about 5 to about 40 mils.
References Cited UNITED STATES PATENTS 2,271,614 2/1942 Baselt 117-29 2,294,930 9/1942 Palmquist 117 29 2,378,252 6/1945 Staehle 117- 33 2,440,584 4/1948 Heltzer et al 117-33 2,974,104 3/1961 Paine et al 117-100 WILLIAM D. MARTIN, Primary Examiner.
S. W. ROTHSTEIN, P. F. ATTAGUILE,