US2934997A - Cinematograph screen having improved properties - Google Patents

Description

May 3, 1960 T. s. HARKNEss CINEMATOGRAPH SCREEN HAVING IMPROVED PROPERTIES Filed Feb. 25. 1957 2 Sheets-Sheet l May 3, 1960 T. s. HARKNEss 2,934,997

CINEMATOGRAPH SCREEN HAVING IMPROVED PROPERTIES 2 Sheets-Sheet 2 Filed Feb. 25, 1957 trade as a hot spot or glare spot.

Patented May 3, 1960 CINEMATOGRAPH SCREEN HAVING IMPROVED PROPERTIES Thomas Smith Harkness, Balham, London, England, as-

signor to AndrewVSmith Harkness Limited, Loudon, England, a British company Application February 2s, 1957, serial No; 642,292 Claims priority, application GreatBritain April 5, 1956 7 Claims. (Cl. Sil-28.9)

This Vinvention relates to projection screens for use, for example, in cinemas and is concerned with a projection screen of the lcind having a base made of a fabric or synthetic plastic material ,rovided on one side thereof with a coating or coatings to give the desired final screen surface. A particularly suitable plastic material base is thatmade from sheeted polyvinylchloride which is coated with titanium dioxide.

It heretofore had been proposed to provide, on such a base, a final screen surface by coating oneside of the base (i.e., that side bearing the titanium dioxide coating) with a multiplicity of layers of a luster paint conveniently made of a lead compound in crystalline form, such as crystalline basic lead carbonate, mixed with appropriate quantities of nitro-cellulose and butyl acetate.

Such a paint gives an excellent screen surface for the smaller size of screen and for narrow halls, but for the large, wide and sometimes curved screens now in use in many cinemas for motion picture presentation the illumination from a single light source often results in an uneven angular reflection of light from the screen Which shows an area of excessive brilliance or glare on the screen-a phenomenon frequently referred to in the In reality, the glare is due to a rapid falling ofi in the amount of light l reflected from the screen center towards the sides and achieved by mixing stearic acid and its fatty acid asso` ciates or its compound in the form of a metal stearate with the crystalline luster paint so that the light reflection from the crystals is influenced in such a way that the distribution of reflected light is widened over a larger Yangle in the horizontal as well as the vertical direction.

States Patent Bice Stearic acid of commerce is mostly associated with other fatty acids of a similar nature such as palmitic `acid and oleic acid and is very suitable as and additive to the crystalline lead compound essence forming the basis of the luster paint, especially Where these exist in crystalline form and are White in color or colorless.

It has been found that stearic acid mixtures associated with similar fatty acids are advantageous as they form mixtures in which. the crystals are of needle and leaf shape structure and intermix very well with the plateshaped crystals of basic lead carbonate when this latter ingredient forms the basis of the luster paint essence.k

.whilst if they are intermixed between the crystrl plates lthey have an additional tilting effect on the crystals. The

result of both these effects is a widening of the angle of distribution of the reflected light.

In the drawings:

Figure 1 is a graph showing the angular distribution and intensity of light reflected from the screen of the invention and selected screen coatings of the prior art.

Figure 2 is an enlarged view, partially in section, of a screen constructed in accordance with the invention.

Instead of stearic acid per se, the metal stearates haveing a white color may be used, for example, zinc stearate.

The nature of the invention will be more readily understood from Fig. 1 of the accompanying drawing in which the line O-H represents the angular horizontal distribution of light reflected from the screen whilst the line O-V represents the vertical angular distribution of reflected light.

The line O-L represents the amount of light reflected in foot lamberts per foot candle. The line A-A represents the light reflected from a screen coated with magnesium carbonate and forming the standard reference as the amount of light reflected from such a screen is ndependent of the angle at which the surface of the screen is viewed. As illustrated by the drawing, the light reflection is substantially constant but low at all `angles which means, in practice, that van appreciable amount of light is lostby being reflected 0n to the walls, floor and ceiling of the cinema.

To concentrate the light more usefully in the auditorium, particularly one of any size, a screen with a higher reflectivity in the center has to be used. One example of such a screen is that coated with a crystalline lead compound luster paint-specifically, crystalline basic lead carbonate-and the light reflection curve of this type of screen is illustrated by the line B--B. lt will benoted that such a screen surface has a narrow angular distribution of light and this makes it eminently suitable for narrow auditoria but as the falling off in reflection is rather steep it is not so suitable for wide halls or cinemas. This is because the rather steep drop in reflectivity becomes visibly apparent under such circumstances as a glare spot on the screen due to the greater' reflectivity in the middle of the screen than at the sides.

A correction of the reflectivity characteristic of the screen is therefore desirable to make it suitable for a wide auditorium, and it has been found that the use of an additive to the luster paint essence of the type referred to above gives a practicable solution to the problem since it results in a screen having a characteristic similar to that illustrated by the line C--C of the drawing. It will be noted that the value ofthe reflection in the middle of the screen is lowered but the angle of distribution of the reflected light so widened that even up to a viewing angle of -which would represent the extreme end row seats in van averagely wide cinemathe amount of light inthe horizontal direction rises above even that from the standard magnesium carbonate screen represented by the characteristic A-A.

Fig. 2 is a diagrammatic representation of a cross-sectional view of a projection screen embodying principles of the present invention. In Fig. 2, the base material is represented at 1, and at 2 an intermediate coating of polyvinyl chloride paint pigmented with titanium dioxide is shown. In the surface coating basic lead carbonate crystals and interspersed stearic acid crystals are shown at 3 and 4 respectively. v

To' make up the paint preparatory to coating the screen, and as an example of the method of carrying the invention into effect, a luster paint essence consisting, by weight, of approximately 35 percent basic lead carbonate crystals, 10 percent nitrocellulose and 55 percent butyl acetate is mixed with approximately l5 percent crystalline stearic acid.

As already mentioned stearic acid as usually available industrially is associated with palrnitic and oleic acids. A sample of a very suitable stearic acid, which was obtained commercially, showed on analysis that it consisted of 43 percent stearic acid associated with 52 percent palniitic acid and 5 percent oleic acid.

The crystalline form of this mixture is mostly-needle shaped and has a setting point of 60 C.

After the luster paint essence and stearic acid additive have been mixed together they are added to a suitable lacquer which is then thinned to the desired consistency to make the tinal paint for coating the screen base. erably, the lacquer is a polyvinyl lacquer prepared by dispersing about 92% of polyvinyl chloride solids and about 8% of copolymerized vinylacetate solids in ketones and aromatic hydrocarbons, the latter being used in amounts to yield a sprayable lacquer composition. A screen coated with a uniform continuous layer o'f such a paint will have a reflection characteristic substantially the same as that illustrated by the line C-C.

When the screen base material is made of polyvinylchloride the use of stearic acid as the additive has the great advantage that it forms a protective layer which prevents the leaching out of the plasticizer from the base material.

The amount of the stearic acid can be varied up to approximately 30 percent by weight of the initial luster paint essence which will result in a great degree of ilexi'oiiity in the final characteristic obtained and make it possible to provide a close approximation to the requirements ot a customer and as dictated by the shape of the cinema auditorium or hall.

' in the case where metal stearates are used instead of stearic acid the necessary percentages of the amount of the additive are best obtained by experiment but, generally speaking, are lower. For example, where zinc stearato is used a much smaller percentage is required since it has been found that o'nly approximately 2 percent of zinc stearato will give the sarne results in widening the angular distribution of light as percent of stearic acid per se. ln general, the size of the metal stearato crystals corresponds to that of stearic acid crystals.

The paint is advantageously applied to the screen surface by automatic spraying means or by roller coating apparatus and in a plurality of individually thin layers.

Specic example in the following illustrative but not limitative example, the term gallon means an imperial gallon (=277.42

cubic inches).

nto 7.5 gallons toluene there are introduced, with agitation, 23.4 lbs. of VYNS vinyl chloride-acetate resin and l5.6 VYHH vinyl chloride-acetate resin, and to the resulting mixture there are added 5.5 gals. methyl ethyl ketone, 8.() gals. methyl isobutyl ketone and 2.() gals. diacetone alcohol, andthe resulting initial solution is stirred until homogeneous.

12.0 pounds of crystalline stearic acid of commerce are wetted with .05 gallon of toluene and thereupon introduced into and thoroughly blended with the abo've initial solution." The viscosity ot the resulting syrup is approximately 4G Ford cup.

lnto this syrup there is added, with thorough mixing, an amount of retlectance-moditying composition (about to' be described) correspondingto 1.5 lbs. per each l (one) gallon of the above syrup. Said reflectance-modifying composition consists essentially of a suspension of basic iead carbonate crystals, 35% by weight, in a butyl acetate, 55% by weight, solution of nitrocellulose, 10% by weight.

Then, to the above mixture there is added, with agitation, a volume of said initial solution" equal to the first,

Pref-l Methyl ethyl ketone Methyl isobutyl ketone Diacetone alcohol Toluene 20 The so-thinned mixture, after having been made hornogenco'us by stirring, has a viscosity of about 20 Ford cup, and is adapted to be applied by spraying to the prepared u material. Said thinned mixture is applied to the ,f lered base material by means of known automatic spraying machinery, in one or more-usually, in twocomplete coats each composed of 4 strokes. After drying, the final surface coating has a thickness of from 2G to' 30 microns.

This application contains subject matter in common with my copending application Ser. No. 607,357, filed August 3l, 1956, for Cinematograph Screens.

I claim:

1. A cinematograph screen comprising an opaque white screen base material in sheet form and on one side of said base a surface coating layer comprising the solids content of a lacquer composition comprising a binder ingredient and a solid reflective ingredient in lamellar or plate-like crystalline form, wherein the lamellar crystals of the lacquer composition are intermingled with a crystalline organic material of the group consisting of commercial stearic acid and metal salts of stearic acid, said crystalline organic material being in needle and leaf forms and serving to tilt the lamellar crystals at a variety of angles with respect to the opaque White screen base material.

2. A directional cinema reflection screen comprising an opaque white screen base material in sheet form and on one side of said base a surface coating layer consisting essentially of the solids content of a lacquer composition containing dispersed therethrough lamellar crystals of basic lead carbonate and a crystalline organic compound selected from the group consisting of crystalline commercial stearic acid and colorless and white crystalline metal stearates, said crystalline organic material being in needle and leaf forms and being intermingled amongst said lamellar crystals.

3. The screen defined in claim 2 in which commercial stearic acid is a mixture consisting essentially of stearic, palmitic and oleic acids wherein the percentage of stearic acid is .43, of palmitic acid 52 and oleic acid 5.

4. A directional cinema reection screen comprising an opaque white screen base material in sheet form and on one side of said base a surface coating layer consisting essentially of the solids content of a lacquer composition containing dispersed therethrough lamellar crystals of basic lead carbonate and a crystalline stearic acid cornpound in needle and leaf forms serving to tilt the lamellar crystals at a variety of angles with respect to the opaque white screen base material.

5. The screen defined in claim 4, in which the stearic acid compound is Zinc stearate in the form of needle-like crystals.

6. The screen defined in claim l, in which the binder ingredient includes a polyvinyl resin.

7. A directional cinema reflection screen comprising an opaque white screen base material in sheet form and on one side of said base a surface coating layer comprising the solids content of a lacquer composition comprising a polyvinyl resinous binder component and dispersed therethrough lamellar crystals of basic lead carbonate and crystalline commercial stearic acid in needle form, wherein the lamellar crystals of basic lead carbonate are tilted at a variety of angles with respect to the screen base material by the crystalline commercial stearie acid in needle form.

References Cited in the le of this patent 5 UNITED STATES PATENTS Hill Feb. 4,v 1919 Hewitt July 10, 1928 Cawley Feb. 18, 1930 Suzuki Dec. 20, 1932 10

Claims (1)

1. A CINEMATOGRAPH SCREEN COMPRISING AN OPAQUE WHITE SCREEN BASE MATERIAL IN SHEET FORM AND ON ONE SIDE OF SAID BASE A SURFACE COATING LAYER COMPRISING THE SOLIDS CONTENT OF A LACQUER COMPOSITION COMPRISING A BINDER INGREDIENT AND A SOLID REFLECTIVE INGREDIENT IN LAMELLAR OR PLATE-LIKE CRYSTALLINE FORM WHEREIN THE LAMELLAR CRYSTALS OF THE LACQUER COMPOSITION ARE INTERMINGLED WITH A CRYSTALLINE ORGANIC MATERIAL OF THE GROUP CONSISTING OF COMMERCIAL STEARIC ACID AND METAL SALTS OF STEARIC ACID, SAID CRYSTALLINE ORGANIC MATERIAL BEING IN NEEDLE AND LEAF FORMS AND SERVING TO TILT THE LAMELLAR CRYSTALS AT A VARIETY OF ANGELS WITH RESPECT TO THE OPAQUE WHITE SCREEN BASE MATERIAL.

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