DE2015548B2 - REAR PROJECTION SCREEN - Google Patents

Description

of the greatest importance

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assessed projection screen may have a slightly higher rating for one rating and a slightly higher rating for a other assessment has a slightly lower "Q value", so that a mean value is obtained from the individual assessments can be formed. The average values obtained in this way win all the more in expressiveness, the more assessments of the projection screen to be tested by different test persons be performed.

Known rear projection screens generally have Q values of around 24, at most around 28, although some of the criteria that result in the Q value are always bad and in need of great improvement. B. a common known projection screen consisting of a glass plate with an applied diffusion layer made of wax has a y-value of 24 with very poor flicker effect assessment and moderate brightness. A conventional known projection screen of another type of a film on acrylic acid base having applied thereto wax diffusion layer yields a Q value of 28, can be un ^C. '^{"Bezu g} spot effect and in particular brightness much to be desired. A further known projection screen of another type of a polyvinyl chloride film with diffusion additives

^{Q on 24 on at moderate} ^ ^{r Η}

^{Very Poor} ™ bad effect assessment.

From the given assessments and Q-widths it ^{follows that all} tested known projection screens are to be assessed badly at least with regard to one criterion, so that their use as rear projection screens is noticeably impaired. ^{Bd the} "W **" * ". tested projection ^{screens are common} commercial products and there are currently no projection screens of the

^{given Ty} , f ^{s sehandeIt} '* ^{by ehl better} ' ^s ' with a higher Q value to be assessed overall

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^{The object of the Erfindu} "g ^is> ■ specify *" Projection t ₅ screen with Bewertungsnofen for each of the four criteria of at least 7 and given a "Q value" ^de r given definition of a minimum of 28 and a process for its preparation.

^{The Erfindun} 8 ^lie 8 ^{l E} ^ kennfnis based on that, the object indicated in particularly advantageous o

^{Manner by lösba} ^ ^{'is a} polypropylene film ^that well-defined type is produced with relatively small crystalline spherulites in the surface regions

* ₅ The invention relates to a rear projection screen of polymers with a degree of crystallinity which is characterized in that is composed of the ^{shade Pol} y P ^r "pylene with a particular according to ASTM Test Method D 1238 melt flow rate of not more than 90 and a thickness from about 500 to about 2000 μ and that the screen further consists of at least about 60 percent by weight of crystalline spherulites with an average diameter of about 5 to about 20 microns and has ^a core area which is at least three ^{quarters of the thickness of the screen} and in ^{Compare the two} surface areas of the screen with comparatively large crystalline spherulites ^{with a} diameter of about 15 to about 45 microns.

The invention also relates to a method for producing the rear projection screen, which thereby is marked that one

^{a) initially an approximately 500} strong ^{to 200} ° ¥ ■, molten film of a polypropylene having ^{an after AS} ™ - stmethode ^Te D 1238 specific melt flow rate of greater than approximately 90 ^{with minde} least one of a temperature as ^{about 85 to 170 ° C befindlicne} n brings the surface of a heat exchanger into contact ^{until b} ' ^sd ' ^e surfaces of the foil are solidified, and ^{b) then the} solidified surfaces of the ^{foil are heated to a} temperature of about ^{85 to 160C} for a long time, up to at least three quarters of ^{the core zone of the Foil} , based on the total ^{thickness of the foil, are>} practically crystalline. To carry out the method of the invention, the melted polypropylene is in the form of a cast or extruded film of the specified thickness on a heat exchanger, the surface of which is at the specified temperature, that is, the temperature of which is low enough to solidify the film surfaces, but is not so low, that the entire film solidifies, applied, whereupon the solidified surfaces of the film are heated to the specified temperature in order to increase the speed of the heat flow to the hem

piece to keep the film comparatively low and to stimulate crystal growth in the core of the film, so that the specified high crystallinity is achieved will. In process stage a), the surface of the heat exchanger is usually immediately in front of it bringing it into contact with the melted film at a temperature in the specified range, preferably kept at a temperature of about 90 to 150 ° C.

Maintaining a film thickness of around 500 to 2000 μ has proven to be very important. Thinner Polymer films of the specified type are either useless as rear projection screens or they are have properties that do not allow the high »Q values« to be achieved. on the other hand Thicker foils with a thickness of more than about 2000 μ are also unsuitable, since they are obviously nor do they lead to rear projection screens with the desired high "Q value".

According to a preferred embodiment of the method one of the two surfaces of the film is a uniform surface roughness in the form of unevenness of about 25 till 26 cm x 10 ~ ^e in a statistically random distribution given. In this way, the light diffusion is increased even further and light reflection from the room or background light on the screen surface being viewed is switched off. The film obtained can be used directly as a self-supporting rear projection screen.

If the projection screens obtained according to the invention are used to produce longer line negatives Reading pamphlets, it has been found to be particularly advantageous to read such negatives through a to consider a comparatively dark layer of paint with a neutral density. This can e.g. B. in the way take place that dyes of neutral density or dye combinations either for the production the film used added polypropylene or on the projection screen obtained according to the invention be applied in the form of a layer, the dyes being used in such an amount that a significant increase in diffusion density, i.e. H. a density increase of 0.1 or more is achieved. If necessary, a thin, transparent polymer film can also be used to read such negatives is colored with a dye of neutral density, in combination with that obtained according to the invention Projection screen can be used. When using such a polymer film needs the dem Surface of the projection screen facing the viewer not to be roughened, but the polymer film used can have a roughened surface exhibit.

The invention is illustrated in more detail by the figure, which shows a greatly enlarged vertical cross section through one for use as a projection screen represents suitable polypropylene film.

In the cross section through a film shown in the figure, the distribution of the polypropylene crystals is Different size and number recognizable.

This polypropylene film was coated with a melt viscosity of 2.5 and a density of 0.90 g / cm ³ at a temperature of 220 ° C directly to the surface of a steel roller whose surface temperature was maintained at 90 ⁰ C, is extruded, the film used had a Thickness of 762 μ. The temperature of the air surrounding the roller was maintained at 93 ° C. The diameter of the cooling roller used was 6.35 cm and the melted polypropylene was continuously deformed into a film at a speed of 0.9 m / min. The extruded film was brought into contact with the surface of the steel roller for a total of 9 seconds. It was found that the specified time was sufficient to solidify the surface of the film with the formation of thin areas of polypropylene of suitable crystallinity on both surfaces of the film.

ιό The film obtained was then on the surface a second roller of the same type and there under the same conditions as on the first Roller held. After leaving the surface of this second, comparatively cold roller, the film was

is fed into a vertical chamber in which the air temperature was kept at 93 ° C. The temperature of the film surface and the air surrounding the film was ^{kept at 93 0} C for a total of about 90 seconds in such a way that the film was exposed to a series of

ao electric heaters running along the length of the Chamber arranged rollers were mounted, was passed. While performing, 'the Foil through the vertical chamber, the foil became highly translucent, which was due to the fact that

«5 in the core zone of the film a large number of comparative formed large crystals with a diameter in the specified range.

The resulting film was then peeled from the chamber and cooled to room temperature under normal conditions. The cooled film was then cut into individual pieces to the desired size of the rear projection screens, whereupon these were provided with a roughness pattern on one side in such a way that they were placed in a conventional hydraulic press under a pressure of 9.84 kg / cm ² a smooth steel plate and a roughness of a 63.5 x 10 cm ~ ^e having plate were pressed.
The rear projection screens obtained in this way had a "Q value" of 31, ¹ which was made up of the following ratings for the four criteria specified:

"Light spot
4 ₅ effect Flicker
effect Con
touch Bright
speed Q value 7th 8th 9 7th 31

The results show that the film represents a projection screen that does not conform to any of the four specified Criteria is to be assessed worse than with the assessment mark 7 and is therefore more advantageous Way is characterized by a very balanced spectrum of beneficial properties

For comparison purposes, some known, commercially available rear projection screens were after specified method of determination. In the case of the usual, known, designated below with A The rear projection screen was made of a glass plate that was provided with a diffusion layer of wax. The tested device under test B was a rear projection screen made of an acrylic acid-based film, also with a wax diffusion layer was provided. Test item C was a known rear projection screen on a polyvinyl chloride film with diffusion additives.

The results obtained are shown in the table below

Luminous
spot
effect Flicker
effect 7th contrast brightness Q-Wen umbrella 9
7th
9 2
8th
2 8th
"9
9 5
4th
4th 24
28
24 A.
B.
C.

The results show that the known rear projection screen A has a Q value of only 24 and has a considerable flicker effect and that the projected image is not particularly bright.

The results also show that the known screen B had a Q value of 28 in a spot evaluation out of 7 and one very unsatisfactory

Has a brightness rating of only 4, and that the known screen C has a comparatively inferior one Q value of only 24 and a noticeably poor assessment of the flicker effect and brightness having.

In further experiments, the projection dish was used in a usual known, for projecting the image ?! on the side facing away from the viewer intended for the projection of small pictures

ίο photocopies printed on a transparent color film were recorded. It was found that the screen obtained according to the invention passed through a very sharp image that was not only free of unwanted haze but also very faithful to the original Color reproduction of the color image on the original, guaranteed.

1 sheet of drawings

309512/40;

Claims (6)

Claims: processing devices of the various types known in which an image located on a microfilm in which 1. Rear projection screen made of polymers with rule through several lenses and after back reflection a certain degree of crystallinity, as a result of one or more deflecting mirrors on the characterized in that the screen of poly projects the side of the screen facing away from the viewer propylene using an ASTM test method. D 1238 certain melt flow rate of at most There are already a wide variety of processes 90 is built up and has a thickness of about 500 to the production of such rear projection screens about 2000 μ and that the screen is also known from substances of various kinds, so at least about 60 percent by weight from crystalline - For years, rear projection screens were made of approximate spherulites with an average etched glass, which if necessary, to make these screens translucent with a diameter of about 5 to about 20 microns, with a high proportion of diffuse light and a core area that is suitable for this purpose Fabrics coated at least three quarters of the thickness of the screen were produced. A disadvantage of such glass power and compared to the two surface screens, however, is their fragility ne spherulites with a diameter of rear projection screens made of plastic or wax about 15 to about 45 microns contains ^ _1- like substances that are not as fragile as glass, 2. Rear projection screen according to claim 1, can therefore be produced. Thus, in the production of reverse throughput that he 20 projection screens microcrystalline wax Transfer on unevenness of about 25-76 x 10 cm ^β applies a rough surface. Typical rear-projection screens that can be manufactured from plastic move with the help of such known references. 3. Processes for the production of backpros or polymers are made of laminates projection screens according to claim 1, characterized, for example, in such a way that a top characterizes 25 areas of clear, stiff plastic film with a dark a) there is an approximate 500 to 2000 μ thick ascending ^len 'opaque dye-containing layer vergeschmolzene film ^{is seen} from a polypropylene' ^{or of} several similar Polymensatmit one by ASTM Test Method D 1238 ^{fol 's} <, for example, made of polyethylene certain melt flow rate of at most. ^From U.S. Patent 3,372,971 is a back pressure about 90 with at least one known on a ³ ° projection screen, consisting of at least two, temperature of about 85 to 170 ⁰ C located ^{in the Re} S ^{el three inni} S interconnected Surface of a heat exchanger as long as there is layers, of which at least one consists of brings in contact until the surfaces of ^a mixture of polyethylene and polypropylene and Film are solidified and at least one other made of a copolymer b) then the solidified surfaces of the ^{35 is made up of} polyethylene and polypropylene. Foil ₁₀ long to a temperature of about ^This known screen, whose translucency is ^{heated to 85 to 160 0} C, up to at least three optical incompatibility of the substance quarters of the core zone of the foil that make up it, based on components, but not on their crystallinity however, the total thickness of the film, which is practically crystalline, has numerous disadvantages. _s j _nc | 40 So it is disadvantageous that a wide variety of materials are required for its manufacture that 4. The method according to claim 3, characterized in that several layers are intimately and flawlessly characterized in that a film with a thickness of must be connected, that these bonds are used for about 635 to 1525 μ and these are extremely important in the achievable optical effects Process stage a) are at a temperature of 45 and that the layers forming the screen of about 90 to 150 ^° C. are comparatively thick. a heat exchanger brings into contact as well as those producible with the help of the known methods show the solidified surfaces of the film obtained in projection screens of the specified type process step b) to a temperature of, however, numerous other disadvantages which heats about 90 to 120 ⁰ C. 50 mainly their permeability properties 5. The method according to claims 3 and 4, da- and / or optical criteria, which are characterized for the viewer by the fact that one of the projected images are also important, concern the two surfaces of the polymer film an easy assessment and evaluation of Rückprof Roughness in the form of unevenness projection screens, in which the image is ^{projected onto the side facing away from the Beiron about 25 to 76 · 10 "6} cm in a statistically random manner, gives distribution 6. The method according to claim 5, characterized by optical behavior significant criteria, namely shows that one of the two surfaces has a (1) »contrast«, (2) »brightness«, (3) »flicker roughness pattern after a tempera effect «and (4)» light spot effect «. This surface is reduced to below about 85 ° C. 60 An ideal rear projection screen of the specified is rigt. Type has practically no "light spots", i. H. no districts with much greater brightness than that the rest of the screen surface, furthermore it has practically no "flickering", i. H. none on the The invention relates to a rear projection screen 65 surface of the screen occurring tiny glittering from polymers with a certain degree of light spots, with maximum image contrast as well Crystallinity and a method for its production. great brightness. From the specified criteria There are already rear projection screens in view- are the "Leu.chtfleckeffekt" and the "Flimmereffekf"