JPH05247456A - Luminescent article with protective coating and manufacture of the same - Google Patents

Abstract

PURPOSE: To provide a luminescent article capable of keeping an excellent resolving power by coating a phosphor-contg. resin layer with a radiation-curable liquid compsn. having specified properties, giving the coating an embossed structure and curing it by a radiation.

CONSTITUTION: Phosphor particles (e.g. Gd₂O₂S:Tb) are dispersed in a resin binder (e.g. polyethyl acrylate) and the obtained dispersion is applied to a support and dried. Then, a radiation-curable liquid compsn. having a viscosity of at least 450 mPa.s as measured with a Hoeppler viscometer, which does not penetrate into the phosphor-contg. layer, is applied to the obtained phosphor- contg. layer. After giving the coating to have an embossed structure, the coating is cured with radiation to form a protective layer. Thus, the luminescent article having the protective layer having a thickness d of 1 to 50 μm and such an embossed surface roughness Rz that the ratio of the surface roughness Rz to the layer thickness d is at least 0.35 is obtained.

COPYRIGHT: (C)1993,JPO

Description

Detailed Description of the Invention

The present invention relates to luminescent articles having a coating of phosphor particles and a protective coating applied thereto.

In a radiograph, the inside of the object is X
Rays, γ rays, and high energy elemental particle radiation, eg β
Reproduced by penetrating radiation, which is a high energy radiation belonging to the group of rays, electron beams or neutron radiation. Luminescent materials, called phosphors, are used to convert transmitted radiation into visible and / or ultraviolet radiation.

In conventional radiography, X-rays are image-wise transmitted through an object by means of X-rays converted into light of corresponding intensity in a so-called intensifying screen (X-ray conversion screen). The resulting, in this case, phosphor particles absorb the transmitted X-rays and convert them into visible light and / or UV radiation which the photographic film is more sensitive to than the direct impact of X-rays.

In fact, the light image-wise emitted by said screen illuminates the photographic silver halide emulsion layer film in contact, which is developed after exposure to form a silver image therein which is in agreement with the X-ray image.

In conventional medical radiography, an X-ray film comprises a transparent film support coated on both sides with a silver halide emulsion layer. During x-ray irradiation, the film is placed in a cassette between two x-ray conversion screens, each contacting their corresponding silver halide emulsion layer.

One-side coated silver halide emulsion films combined in contact with only one screen are often used in autoradiography, in applications where improved image clarity is of great importance, eg in mammography and in industrial applications. Used in the special field of non-destructive testing (NDT) known as radiography. An autoradiograph is a photographic record formed through the intermediate of penetrating radiation emitted by radioactive material contained in objects such as microtome cuts for biochemical studies.

Phosphors suitable for use in conventional radiography have high prompt emission articles when exposed to X-rays,
It must also have the advantageous low afterglow that it has for image sharpness.

Recently, use has been made of photostimulable storage phosphors which, in addition to their fast light emission upon irradiation with X-rays (prompt emission), have the property of being able to temporarily store most of the energy of the X-ray image. An X-ray recording method was developed. The energy is emitted by the photostimulation in the form of light that differs in wavelength characteristics from the light used for photostimulation. In the X-ray recording method, the light emitted during photostimulation is detected photoelectrically,
Sequentially converted to electrical signals.

The basic building block of such X-ray imaging methods operating with storage phosphors is an imaging containing said phosphor, which is usually a plate or panel that temporarily stores an X-ray energy pattern. Sensors, scanning laser beams for photostimulation, opto-electronic photodetectors that provide analog signals that are sequentially converted to digital time series signals, digital image processors that process digital images normally, signal recorders such as magnetic disks. Or image recorders or electronic signal displays for the modulated exposure of tapes and photographic films, such as cathode ray tubes.

From the above description of the two X-ray recording methods operating with an X-ray conversion phosphor screen in the form of a plate or panel, said plate or panel acts only as an intermediate imaging element, It is clear that it does not form a record. The final image is created or reproduced on another recording medium or display. The phosphor plate or sheet can be reused repeatedly.
Prior to reuse of the photostimulable phosphor panel or sheet, the residual energy pattern is erased by irradiation with light.
The expected life of the plate can be limited primarily by mechanical damage such as scratches.

Both types of X-ray conversion screens generally comprise, in the following order, a support, a layer containing phosphor particles dispersed in a suitable binder, and a phosphor containing layer to protect said layer during use. Includes a protective coating coated on the layer.

Since the X-ray conversion screens are used repeatedly in the X-ray recording method described above, it is important to provide them with a suitable overcoat to protect the phosphor-containing layer from mechanical and chemical damage. is there.

The protective layer preferably has a relief structure that reduces friction as well as the tendency to exhibit sticking phenomena with the materials in contact. Therefore, the relief structure is advantageous for loading / unloading the film into / from the cassette, and is advantageous for reducing the accumulation of static electricity. Especially in automatic loading for daylight, for example, C
In URIX CAPACITY (trademark of Agfa Gewert), the reduction of electrostatic build-up as a result of friction phenomena during cassette loading and unloading is a function of the distance and contact area between the screen and photographic film. Once the cassette is loaded, the contact between the film and screen needed to obtain good image quality is enhanced by the application of pressure at the cassette surface. As a result, the air contained between the screen and the film surface escapes and a vacuum is created in the cassette. The sticking phenomenon resulting from said contact must be avoided, while the post-exposure vacuum break must be accelerated when the cassette has to be opened and the film brought to the processing equipment. So for example US
Solid particles protruding from the protective coating can be incorporated as described in 4059768.

However, providing a relief structure that efficiently improves the operation as described above sacrifices image quality. In fact, the provision of protruding particles requires an increased thickness of the protective coating, resulting in reduced image sharpness due to the increased distance between the radiation-emitting phosphor layer and the radiation-sensitive coating of the photographic film in contact therewith. Let

Not only does the increased thickness itself lead to an increased unsharpness of the emitted light when the binder binder of the phosphor coating and the binder of the protective coating differ, but also the bonding of the protective coating. The presence of the particles themselves, which have a different refractive index compared to the refractive index of the agent, also causes non-sharpness.

The terms x-ray conversion screen and phosphor as used herein refer to screens and phosphors for use in conventional screen-film combinations and for stimulated luminescent radiography. In the latter case, an improved operation, in particular the transport of the screen, is required, since the screen itself has to be transported from the exposure location to a device which has to read it by stimulating light.

The roughening of the protective layer by the addition of a coating of solid particles, for example polystyrene beads having a diameter of 25 .mu., Promotes the transport properties of said layer, but because these particles are scraped off, they are abrasion resistant. Has a disadvantageous effect. Furthermore, the thickness of the protective layer varies with the roughness rate, and the effect of the solvent used, the coating temperature and the drying conditions is directly related to the penetration depth of the particles, such as polystyrene beads, in the coating layer, so that It also depends largely on the viscosity. As a result, the actually measured thickness depends on the amount of protrusion of the particles.

The object of the present invention is to have a phosphor-binder layer and a protective coating applied to it, the protective layer having a relief structure for highly easy operation, whereby adhesion,
The object is to provide a luminescent article, for example in the form of a plate, panel or web, which avoids friction and electrostatic attraction and is accompanied by the maintenance of good resolution.

Other objects and advantages of the invention will be apparent from the following description and examples.

According to the present invention there is provided a luminescent article comprising a self-supporting or supported layer of phosphor particles dispersed in a resin binder, provided with a protective coating having an embossed structure, in particular a protective coating. Has a layer thickness d of 1 to 50 μ and has an embossed surface roughness R _Z , the ratio between the roughness R _Z and the thickness d being at least 0.35. The embossing protection layer is
(1) on the phosphor-containing layer, at a coating temperature, having a viscosity of at least 450 mPa.s measured with a Heppler viscometer,
By coating a liquid radiation curable composition that does not penetrate into the phosphor-containing layer to a substantial extent, (2) providing an embossed structure to the coating, and (3) curing the coating with radiation, It can be provided on the phosphor layer to protect it against mechanical and chemical damage.

The roughness and thickness correlative features of the protective coating provide the screen of the present invention with the desirable and surprising properties of ease of operation and excellent image sharpness.

The thickness d of the protective layer of the phosphor screen formed according to the present invention is 1 to 50 μ, preferably 2 to 30.
μ, more preferably in the range 3 to 25 μ, which gives a very flexible and sufficiently abrasion-resistant coating.

The thickness of the protective layer depends on the microscope cross section (intersection).
s) or with a thickness measuring device on a microscale, the roughness R _Z must be measured as the arithmetic mean roughness depth value R _t of 5 different but subsequent measuring areas; The value R _t is defined as the height difference between the highest peak and the lowest valley. A device suitable for such microscopically minute measurement is a perthometer, which allows the surface texture to be measured by ANSI B46.1 (1985) published by The American Society of Mechanical Engineers.

The value of R _z for a layer thickness d of about 8 μ, at which advantageous image sharpness is obtained, is at least 3.0 in order to reach a value between the two parameters of at least 0.35.
This value, which should be μ, is referred to as V _Rd and is represented by the notation V _Rd = R _Z : d.

The roughness of the top coating of the intensifying screen is substantially avoided even after the phenomenon of sticking between the film in the cassette and the intensifying screen is in intimate contact due to the pressure generated in the cassette device. Provide the benefits that can be achieved.

In connection with the transport properties of the film in the cassette, the use of an X-ray conversion phosphor screen having an overcoat with an embossed structure favors practically friction-free loading and unloading of the cassette. , Significantly reduce the accumulation of static electricity. Microchannels formed by the embossed structure of the protective coating allow air to escape between the phosphor screen and the contacting film, thereby
Good screen-film-screen contact without the inclusion of large bubbles improves image quality (image sharpness).

According to a preferred embodiment, the coating of the protective layer is carried out by screen printing (silk screen printing).

The screen printing method is a paste consistency coating composition (viscosity of at least 1000 mPa.s at coating temperature) with a fairly small thickness, for example a coating thickness in the range of 2 to 15 μ.
Is preferred.

For more information about screen printing on manual, automatic or semi-automatic printing presses, see the following references, eg Dover Publications Inc. 1963, New York, JIBi.
egeleisen, The Complete Book of Silk Screen Pri
nting Productions and Delmer Publishers In of the US
c. 1988, J. Michael Adams, Printing Tec
hnology 3rd edition, pp. 431-445. Standard screen printing devices have a piece of cloth or screened screen printing frame. For printing (not for simple coating), the sieve is image-wise blocked to form a stencil. A flexible squeezer is used to force the ink (here the radiation curable coating composition) through the sieve opening to reach the substrate, deposit the ink or coating composition on the substrate and separate the sieve. After that, it is dried or cured.

In a preferred embodiment, the protective coating composition is applied by a rotary screen printing device as described in detail in European Patent Application No. 91201009.7 filed April 26, 1991. The above specification is schematically illustrated by the accompanying drawings.

A rotary screen printing device, operating as a coating device, applies a coating composition of paste-like consistency through a seamless rotary screen in the form of a sleeve. Adjustablely placed flexible squeeze blades (made of stainless steel) in the clamp press the paste onto the substrate through the perforated screen wall of the screen. According to the invention, the substrate is, for example, a film support coated with a phosphor-binder layer. The substrate in the form of a web is guided by opposed pressure rollers. The paste-like coating composition is fed through a distribution pipe located inside a rotating screen mounted at the sleeve end to a ball bearing free rotating annulus. The screen is axially tensioned pneumatically. As known to those skilled in the art, thin-walled screens can be made by weaving with natural or synthetic polymeric threads or fine metal wires. According to another method, the screen is made by electrodepositing a metal such as nickel in a screen-like pattern.

A screen having a screen fineness of 10 to 500 lines / cm and an open area percentage (permeation percentage) of 5 to 45% of the total screen surface area is 1000
It has been found that radiation-curable liquid coating compositions having viscosities in the range of up to 5000 mPa.s have been found to give satisfactory results, the viscosities being smaller when the opening structure of the screen is fine. The thickness of the sieve or screen is 50 ~
It may be 150μ, preferably about 100μ, especially smooth, thin flexible protective coatings are 10-1
Thickness in the range of 10μ, 3000 to 45 for 1 cm ²
It can be made using a screen printing device operating with a screen having 00 holes and a hole diameter of 80-40 μm.

A particularly useful high viscosity liquid radiation curable coating composition is a chemically inert polymer dissolved in an addition polymerizable liquid monomer up to the viscosity desired for use in accordance with the present invention. And / or made by addition-polymerizable liquid prepolymer.

A very useful radiation curable composition for forming a protective coating comprises (1) a crosslinkable prepolymer or oligomer, (2) a reactive diluent monomer, and
(3) In the case of UV curable formulations, it contains a photoinitiator.

Typical amounts of these main components calculated on the total coating composition are 30 to 10 for the prepolymer.
0% by weight, 10-70% by weight for reactive diluents, 0-10% by weight for photoinitiators. A small amount of non-reactive organic solvent for the prepolymer (eg 5 wt) may be present if desired.

Examples of suitable prepolymers for use in the radiation curable compositions applied according to the present invention are: unsaturated polyesters such as polyester acrylates; urethane modified unsaturated polyesters such as urethane-polyester acrylates. Liquid polyesters having acrylic groups as end groups, for example saturated copolyesters provided with acrylate end groups, are described in published EP-A 0207.
257 and Radiat. Phys. Chem. 33, No. 5, 443-.
Pp. 450 (1989). The latter liquid copolyesters are substantially free of low molecular weight unsaturated monomers and other volatile substances and have low toxicity (Adaesion 1
990, No. 2, p. 12). German published patent 2 for the production of many types of radiation curable acrylic polyester
838,691. 2 of the prepolymer
Mixtures of more than one species may be used. A survey of UV curable coating compositions can be found, for example, in Coating 1988 September 348-.
Pp. 353.

Other abrasion resistant topcoats can be obtained by using prepolymers, also referred to as oligomers of the group of aliphatic and aromatic polyester-urethane acrylates. The structure of polyester-urethane acrylate is based on Fe, Philadelphia, PA, PA, USA.
R. Constanza, APSilv published in June 1986 by deration of Societies for Coatings Technology
Radiation Cured Coatings by eri and Joseph A. Vona
Given on page 9 of.

The structure of a particularly useful aromatic polyester-urethane acrylate prepolymer has the general formula:

[0039]

[Chemical 1]

In the formula, R is a C ₂ -C ₆ alkylene group.

In the synthesis of the aromatic urethane, tolylene-2,4-diisocyanate was first used in the polyaddition reaction with the aliphatic diol, and the polymerizable double bond terminal structure was used as a terminal isocyanate group and a diisocyanate group. Introduced by reaction with hydroxyl acrylate. Alkylene diisocyanates such as 1,6-diisocyanate hexane are used in the synthesis of aliphatic urethane acrylates.

Examples of the preparation of aliphatic polyester-urethane acrylates are US Pat. No. 4,983,505 and DE 25308.
96.

The introduction of a plurality of acrylic double bonds per polymer chain of the prepolymer is carried out by first partially esterifying the polyol, for example pentaerythritol, with acrylic acid, followed by the still free HO groups of the polyol and the polyfunctional. By reaction with a polar acrylate.

Examples of free radically polymerizable liquid monomers that preferably act as solvents for the prepolymer and are therefore called diluent monomers are: methyl (meth)
There are acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate, n-hexyl acrylate, lauryl acrylate, tetrahydrofurfuryl methacrylate and the like.

The monofunctional diluent monomer does not necessarily have to be used with an unsaturated prepolymer, but with saturated polyesters such as polyethylene terephthalate and polyethylene isophthalate to form a radiation curable composition having good abrasion resistance. Can be used for Preferred monofunctional monomers for use together are methyl methacrylate and tetrahydrofurfuryl methacrylate.

Examples of suitable bifunctional monomers include 1,6-
Hexanediol diacrylate, 1,6-hexanediol dimethacrylate, silicone diacrylate,
There are neopentyl glycol, 1,4-butanediol diacrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate, pentaerythritol diacrylate, and divinylbenzene.

Bifunctional acrylates such as hexanediol diacrylate are preferably used as reactive diluents in an amount of 0 to 80% by weight, preferably 10 to 30% by weight.

Examples of trifunctional or higher functional monomers include trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, dipentaerythritol hexaacrylate, acrylates of ethylenediamine, aliphatic and aromatic urethane acrylates. And a monomer according to general formula (I) described in European patent application 91200468.6 filed on Mar. 5, 1991, published in the above-mentioned application for the production of said monomer. Application 35
22005, 3703080, 3643216, 370
3130, 3703080, 3917320 and 374
3728 is quoted.

When radiation curing is carried out using ultraviolet radiation (UV), a protective layer composition which acts as a catalyst for initiating the polymerization of the monomers and optionally their cross-linking with a prepolymer A photoinitiator is present in the coating composition to act as a catalyst that causes the curing of the.

A photosensitizer may be present to enhance the effect of the photoinitiator.

Suitable photoinitiators for use in UV curable coating compositions are organic carbonyl compounds, for example benzoin ether compounds such as benzoin isopropyl, isobutyl ether; benzyl ketal compounds; ketoxime esters; benzophenone, o. Benzophenone-based compounds such as benzoylmethylbenzoate; acetophenone, trichloroacetophenone, 1,1-dichloroacetophenone, 2,2-diethoxyacetophenone,
Acetophenone-based compounds such as 2,2-dimethoxy-2-phenylacetophenone; thioxanthone-based compounds such as 2-chlorothioxanthone and 2-ethylthioxanthone; and 2-hydroxy-2-methylpropiophenone and 2-hydroxy-4'- It belongs to the group of isopropyl-2-methylpropiophenone, 1-hydroxycyclohexyl phenyl ketone, and the like.

A particularly preferred photoinitiator is 2-hydroxy-
2-Methyl-1-phenyl-propan-1-one, the product of which is E. Merck, Darmstadt, Germany.
Marketed under the trademark DAROCUR 1173.

The above-mentioned photopolymerization initiators can be used alone or as a mixture of two or more kinds.

Examples of suitable photosensitizers are eg GB-P1.
314556, 1486911, US-P425551.
There are special aromatic amino compounds as described in US Pat. No. 3, and merocyanine and carbostyril compounds as described in US Pat. No. 4,282,309.

A radiation curable coating composition, a storage stabilizer,
Colorants and other additives may be added, which are then dissolved or dispersed therein to form a coating liquid for the protective layer. Examples of colorants that can be used in the protective layer are MAKROLEX ROT EG, MAKROLE
X ROT GS and MAKROLEX ROT E2
Including G. MAKROLEX is a registered trademark of Bayer AG, Lefarksen, Germany.

When using UV radiation as the curing source, the photoinitiator that needs to be added to the coating solution will also absorb the light emitted by the phosphor, to some extent.
This impairs the sensitivity of the radiographic screen, especially when using phosphors that emit UV or blue light.
If a green-emitting phosphor is used, the photoinitiator should be selected so that its absorption range overlaps the emission range of the phosphor to a minimum extent, the preferred photoinitiator being DAR.
OCUR1173 ™.

The amount of photoinitiator used was prepolymer 10
It is preferably in the range of 0.01 to 5 parts by weight with respect to 0 parts by weight. In particular, it is preferable to use the photoinitiator in an amount of 0.5 to 3 parts by weight and within a range of 3 to 7 times the amount of the radical generating compound used.

The protective coating of the luminescent article of the present invention provides an embossed structure by passing the uncured or slightly cured coating through the nip of a pressure roller following the coating step.
In this case the roller in contact with said coating has a micro-relief structure, for example the coating is embossed in order to obtain a relief portion having a height such that the ratio between roughness and thickness is at least 0.35. give. A suitable method for forming patterned structures on plastic coatings by engraving chill rolls is described in US-P 3,959,546.

According to another embodiment, the pattern or embossed structure is pre-treated in the coating step with a radiation curable liquid coating composition having a Heppler viscosity of 450 to 20000 mPa.s at a coating temperature of 25 ° C. It is obtained by applying the paste-like coating composition using a gravure roller or a screen printing device.

A device known as a Heppler viscometer and its use for measuring the viscosity of radiation curable coating compositions used in accordance with the present invention is Interscience Publi, a division of John Wiley & Sons in New York and London.
shers 1963, JR Van Wazer, JWLyons,
Viscosity and Flow Mea by KYKim and REColwell
It is described on pages 276-279 of the surement book. 1 mPa.s is 1 centipoise.

To avoid smoothing of the embossed structure under the influence of gravity, viscosity and surface shear forces, radiation curing is carried out immediately or almost immediately after application of the liquid coating. The rheological behavior or rheological properties of radiation-curable coating compositions can be controlled by so-called flow agents. Therefore, lower alkyl (C _1-
The C ₂₎ and higher alkyl (C ₆ ~C ₁₈₎ alkyl acrylate ester copolymer containing ester groups can be used as shear controlling agents lowering the viscosity. Addition of facial mucilage such as colloidal silica increases the viscosity.

Various other optional compounds in the radiation-curable coating composition of the radiographic article of the present invention, such as compounds for reducing electrostatic charge accumulation, plasticizers, matting agents, lubricants, defoamers, etc. Europe Those described in patent application 91 / 201009.7 may be included. In the above-mentioned specification, not only an apparatus and a method for curing but also a description of a binder for an X-ray conversion screen phosphor, a photostimulable phosphor and a phosphor-containing layer are given.

The thickness of the phosphor layer, which can vary depending on the sensitivity of the radiographic screen to radiation, the type of phosphor, etc., is from 10 to 1000 μ, preferably from 50 to 500.
It can be in the range of μ, and more preferably in the range of 150 to 250 μ.

Two or more phosphor layers having different thicknesses and / or different binder to phosphor ratios and / or different phosphor particle sizes can be used.

Radiographic screens, especially those containing conventional non-stimulatory phosphors as described above, are of gradual screens, ie screens having a gradual sensitization along their length and / or width. It can also be in the form. Increasing properties are provided by the phosphor by increasing the thickness of the phosphor layer over the length and width of the screen, or in the protective layer or in the intermediate layer between the protective layer and the phosphor-containing layer. This can be achieved by incorporating increasing amounts of dye that can absorb the emitted light. According to another convenient method, increasing properties are obtained by halftone printing of dye or ink compositions which absorb the light emitted by the screen. By varying the size of the screen dots during halftone printing, i.e. by gradually varying the% dot area over the length or width of the screen, incrementality can be obtained to any degree. Halftone printing can be done on the phosphor-containing layer coated on top with a protective layer, or by applying a protective coating by halftone printing, eg gravure roller or silk screen printing. ..

Non-limiting examples of support materials include cardboard, plastic films such as cellulose acetate, polyvinyl chloride, polyvinyl acetate, polyacrylonitrile, polystyrene, polyester, polyethylene terephthalate, polyamide, polyimide. , Films of cerylose triacetate and polycarbonate; metal sheets such as aluminum foil and aluminum alloy foil; plain paper,
Includes baryta paper; resin-coated paper; pigment paper containing titanium dioxide and the like; paper sized with polyvinyl alcohol and the like.
Preference is given to using a plastic film as support material.

The plastic film can contain a light absorbing material such as carbon black. Alternatively, it can contain a light-reflecting material such as titanium dioxide or barium sulfate.
The former is suitable for making high-resolution radiographic screens, while the latter is suitable for making light-sensitive radiographic screens.

Examples of preferred supports are transparent or blue-coloured or black-coloured polyethylene terephthalate (eg LUMIRR marketed by Toray Industries, Japan.
ORC type X30), TiO ₂ or BaSO ₄
There is polyethylene terephthalate filled with.

These supports may have a thickness which may vary depending on the material of the support, generally 60
~ 1000μ, more preferably 80 ~
It can be 500μ.

Method for coating phosphor layer, solvent and dispersant useful for binder of phosphor-containing layer, useful plasticizer,
Useful fillers and basecoat or interlayer compositions are described in European patent application 91 / 201009.7, among others.

The present invention is illustrated by the following examples, but the invention is not limited thereto. Ratios and percentages are by weight unless otherwise noted.

Example

Production of X-ray conversion screen

A phosphor coating composition was made by intimately mixing the components shown below.

Gd ₂ O ₂ S: Tb polyethyl acrylate (30% in ethyl acetate) methyl ethyl ketone methyl glycol 2-butanone dispersant GAFAC RM610 ™ ethyl acetate

A green light-emitting terbium-doped gadolinium oxysulfide phosphor (80%) was predispersed in a binder low viscosity presolution (20%).

The pre-solution was 7% polyethyl acrylate,
18% ethyl acetate, 50% methyl ethyl ketone, 24.5% methyl glycol and 0.5% GA
It consisted of FAC RM610 ™. Subsequently, a polyethyl acrylate binder and an ethyl acetate solvent were added to the phosphor pre-solution to obtain a solution having a solid content of 70% and a binder of 89% with respect to 11% of the binder. A 200 μm thick polyethylene terephthalate support subbed with the above composition was doctor blade coated at a phosphor coverage of 60 g / m ² and dried. It has to be said that well-known phosphors or phosphor mixtures, either normal or photostimulable, could be coated as this layer.

Production of UV curable protective overcoat

A radiation curable topcoat layer composition was prepared by adding 60/4
It was made by mixing prepolymer and diluent monomer hexanediol diacrylate (HDDA) in a ratio of 0. The mixture of prepolymers comprises (1) an aliphatic polyether-urethane acrylate having 6 acrylic double bonds per polymer chain, an average molecular weight of 1000 and a Heppler viscosity at 20 ° C. of 100,000 mPa.s. , And (2)
Having three acrylic double bonds per polymer chain,
The prepolymer consisted of a 70/30 ratio of aliphatic polyester-urethane acrylate having an average molecular weight of 1500, said prepolymer being mixed with 15% HDDA [(2) Heppler viscosity was 30,000 mPa.s at 60 ° C. ].

Photoinitiator DAROCUR 1173 ™
Was added at a ratio of 5% to the coating composition.

The radiation-curable coating composition had a Heppler viscosity of 1000 mPa.s at a coating temperature of 20 ° C.

In fact, a WORK operating on a cylindrical Stork DLH sieve having a circumference of 64 cm and used as template
Coating was carried out by screen printing using a TM printer PD-IV (mesh 155, thickness 110 μ, opening area 6-8%, diameter of circular opening 43-49 μ). The thickness d of the obtained coating was 8-10 μm. Printing is 4m /
It was done at the speed of minutes. The doctor blade was made from stainless steel with a length of 20 mm and a thickness of 0.2 mm. Further adjustments to the coating machine include 6 units of doctor blade pressure and 2 units.
The height of the doctor blade was 1 unit.

UV radiation curing

The applied radiation-curable coating composition was cured with UV radiation using a Labcure Unit marketed by Technigraf GmbH of Graf-en-Wiesbacher, Germany (air cooling, energy output 80 W / cm,
Speed 4 m / min, distance between UV source and substrate 11 cm).

A series of screens were made with varying roughness R _Z from 1 to 8μ as defined by the persometer measurements described above. To obtain said series of changes, the fluidity was determined, which determined parameters such as doctor blade pressure and height, amount and concentration of solvent added to the phosphor predispersion, squeezing pressure and coating speed.

Transport and operating characteristics were simulated using the vacuum aspiration experiment. In principle, a rubber suction cup was placed on the X-ray conversion screen and a vacuum was created between the suction cup and the screen surface by vacuum suction. Experimentally, the time can be measured at the end of vacuum suction and when the contact between the screen and the cup is broken. Therefore, “Automatic Bekk Smoothness Tester, code 131E” from Buechel-Van Der Korput BV in Benendal, The Netherlands.
D "can be used, can record the relationship between the contact time as shown in FIG. 1 t and screen roughness R _Z. Figure 1 shows roughness R _Z
Indicates that the larger is the shorter the contact time between the screen and the contact material after vacuum suction is due to the easier air transfer between said contact materials.

As can be seen from FIG. 1, the roughness R
_{Z corresponds} to the above-mentioned V _Rd value of at least 0.35 3
When increasing from μ to 8μ, the above-mentioned Automatic Bekk S
The good transport properties associated with the short contact times measured with the moothness Tester are advantageous.

An overall thickness of 8-10 μm for the protective layer favors image sharpness.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between contact time t and screen roughness R _Z.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jean Emile van Avenberg Berg 2070 Zveundlek, Leuvellican Larn 18 Belgium

Claims (12)

[Claims] 1. A luminescent article comprising a self-supporting or supported layer of phosphor particles dispersed in a resin binder, provided with a protective coating having an embossed structure. 2. An embossed surface roughness such that the protective layer has a layer thickness d of 1 to 50 μ and a ratio between the roughness R _Z and the thickness d referred to as V _Rd of at least 0.35. The luminescent article according to claim 1, having R _Z. 3. The thickness d of the protective layer includes 2 to 30 μm.
The light-emitting article according to claim 2, comprising: 4. The thickness d of the protective layer includes 3 to 25 μm.
The luminescent article according to claim 2, which comprises: 5. The luminescent article according to claim 2, wherein the protective layer is a radiation-cured coating. 6. A phosphor-containing layer having a viscosity of at least 450 mPa.s as measured by a Heppler viscometer at the coating temperature and not permeating into the phosphor-containing layer to a substantial extent. 6. A luminescent article according to any one of claims 1 to 5, characterized in that it comprises the steps of coating a liquid radiation curable composition, (2) giving the coating an embossed structure, and (3) curing the coating by radiation. Manufacturing method. 7. The radiation curable liquid coating composition comprises 450-20000 mP at 25 ° C. as measured by a Heppler viscometer.
7. The method of claim 6 having a viscosity in the as range. 8. The radiation curable liquid coating composition is applied by screen printing.
Or the method of 7. 9. The method of claim 8 wherein said screen printing is produced on a rotary screen printing device. 10. The method according to claim 6, wherein the radiation curing is performed by ultraviolet radiation and electron beam radiation. 11. A roughness R _Z is obtained by passing a screen with an uncured or only slightly cured protective coating through the nip of a pressure roller, the roller contacting the coating having a microrelief structure. Claim 6
10. The method according to any one of 10 to 10. 12. The method according to claim 6, wherein the roughness R _Z is obtained in the coating step by applying the coating composition by means of a gravure roller or a screen printing device.