JPH0276484A - X-ray shielding projecting lens - Google Patents

Abstract

PURPOSE:To secure the flame resistance of a base body plastic and to execute the sure prevention of the leakage of an X-ray by manufacturing and assembling a lens barrel with the plastic material to mix a glass lens and an X-ray shielding material. CONSTITUTION:An inner lens barrel 17 fixes a plastic lens 2 and a glass lens 9 to a prescribed position. An outer lens-barrel 18 is for positioning and fixing a plastic lens 4. A lens fitting lens barrel 19 fits and fixes a cathode ray tube 7 and a lens. For the plastic material used for these barrels 17, 18 and 19, materials to shield an X ray, for example, lead compound, barium compound, strontium, titanium, zirconic acid, zinc, antimony, other heavy metal, metal, inorganic substance or the material to mix so as to have an X ray attenuation ratio necessary to shield the X ray to generate the mixture, compound substance, etc., from a tube 7 are used. At least, the front surface of the tube 7 is wholly covered, and the lens has the sealed construction so that the X ray to occur from the tube 7 cannot leak.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to video projectors and X-rays used for shielding harmful X-rays emitted from cathode ray tubes such as televisions and for enlarging and projecting images. This invention relates to a shielding projection lens.

Conventional technology In the past, high-precision optical lenses usually consisted of a combination of a glass lens and a metal barrel, but in recent years plastic molding and cutting techniques have been used to reduce weight. With the progress of lens development, plastic lenses are now being put into practical use.

Plastic lenses are rapidly being adopted for projection lenses that require high-precision, large-diameter lenses.

This type of lens is mostly used in video projectors - televisions;
When a TV malfunctions and a high voltage is applied to the cathode ray tube, X-rays that would not normally be generated are generated from the cathode ray tube's light emitting surface. In glass lenses and metal barrels, these X-rays are absorbed by the glass material of the lens and are not emitted to the front surface of the lens. In addition, X-rays passing through the outside of the glass lens were blocked by the metal lens barrel, and no X-rays leaked to the outside. However, projection lenses that use a combination of a plastic lens and a plastic lens barrel have the disadvantage that the plastic absorbs almost no X-rays, so the X-rays are not absorbed and are emitted to the front of the lens, and leak outside the lens barrel. Was.

Therefore, for the purpose of shielding X-rays, the present applicant previously filed Japanese Patent Application No. 59-219708 (Japanese Unexamined Patent Publication No. 61-98617).
proposed a projection lens as shown in the following publication.

A conventional projection lens will be described below with reference to the drawings.

FIG. 3 is a cross-sectional view of a first example of a conventional projection lens composed of three lenses, all of which are plastic lenses.

In the figure, 1 is a plastic lens barrel, and 2, 3.4 are plastic lenses. Reference numeral 7 denotes a cathode ray tube, and the image projected thereon is projected onto a screen (not shown) via a projection lens.

Similarly, X11A, B, C, D, and E are also emitted to the outside. Therefore, this X-ray must be shielded.

5 can shield the glass plate tear, XvAB, C, D, and E, but X$lA passes through the lens barrel 1 and leaks to the outside. 6 is an X-ray shielding frame that shields xwAA leaking from the lens barrel 1.

Reference numeral 8 denotes a back cover for shielding X-rays generated from the rear surface of the cathode ray tube 7.

As described above, in this conventional example, the glass plate 5 is mounted inside the lens barrel 1 to block the X-rays passing through the lenses 2, 3.4, and the shielding frame 6 and back cover 8 are used to prevent the X-rays from leaking from the lens barrel 1. It is characterized by blocking X-rays.

FIG. 4 shows a second conventional example. In this example, 2°4 is a plastic lens, and 9 is a glass lens. X-rays that try to pass through these lenses can be blocked by the glass lens 9, but X41A that passes outside the outer diameter of the glass lens 9
, F, and G cannot be shielded.

Therefore, X-rays are shielded by an X-ray shielding ring 10 made of an iron plate with an inner diameter hole having a diameter slightly smaller than the outer diameter of the glass lens and a dimension to be joined to the inner wall of the outer lens barrel 12. In this case, as in the first example, the X-ray A is transmitted to the outer lens barrel 12.
The glass lens attachment fixing rib 15 and the X-ray shielding ring fixing rib 16, which position and attach the glass lens 9 and the X-ray shielding ring 10, create a gap between the glass lens 9 and the X-ray shielding ring 10. As a result, it passes through this gap and leaks. Therefore, as in the first example, an X-ray shielding iron frame 14 is provided on the outside of the outer lens barrel 12, and an X-ray shielding iron frame 13 is provided on the outside of the inner lens barrel 11.
The X-rays passing through the lens barrels 11 and 12 must be shielded by the lenses 11 and 14.

Problems to be Solved by the Invention As described above, when using plastic for the lens barrel, unlike when using materials that shield X-rays such as iron, lead, and zinc steel plates for the lens barrel, parallel For X-rays, glass lens 9
However, it is not possible to shield oblique X-rays that are not parallel to the lens barrel and pass through the wall of the lens barrel. Therefore, in addition to the projection lens, the outer periphery of the lens barrel must be surrounded by X-ray shielding iron frames 13 and 14.

Even so, the adhesion between the lens barrel and the shielding steel frame is poor, and a small gap is created from which X-rays leak. Measures are being taken to prevent leaks. This requires metal press molds and parts costs, increases the number of parts, requires more man-hours for assembly, and has many other problems. Furthermore, after assembling the projection lens, it is necessary to measure the X-rays and find the leakage points, so the size and shape of the X-ray shielding steel frame cannot be made safe from the beginning and must be revised repeatedly.
There was a problem. Furthermore, it is well known that plastic lens barrels are required to be flame retardant, and that plastics with various degrees of flame retardancy are commercially available.

The UL standard is a well-known representative standard in the industry for this degree of flame retardancy, and this standard UL-94 includes:
. ■ in that order. (Hereinafter, flame retardancy refers to that based on this standard.) In order to make the base plastic, which is originally flammable, flame retardant, various flame retardants must be added to it. It's included. A typical example is Br in the molecule.
It is a halogenated hydrocarbon having a group, and there is also a mixture with polyvinyl chloride. When X-ray shielding additives such as various metals and inorganic substances are mixed into such flame-retardant plastics, the flame retardancy often disappears.

The present invention eliminates the drawbacks of plastic lenses and plastic lens barrels as described above, and provides a projection lens that maintains flame retardancy and has an X-ray shielding effect.

Means for Solving the Problems The present invention maintains the flame retardancy of the base flame retardant plastic,
In addition, the plastic contains a material that shields the X-rays generated by the cathode ray tube, that is, antimony trioxide, barium sulfate, and a mixture of the two, so as to have an attenuation rate necessary to shield the generated X-rays. The invention is characterized in that it has a structure that blocks X-rays by manufacturing a lens barrel using the lens and combining a plastic lens and a glass lens with the lens barrel.

According to the present invention, it is possible to provide an X-ray shielding projection lens configured to shield X-rays generated from a cathode ray tube without using a separate shield and to enlarge and project an image of the cathode ray tube. .

EXAMPLE An example of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of an embodiment of the present invention. In the figure, 17 is an inner lens barrel that fixes the plastic lens 2 and the glass lens 9 in predetermined positions. 18 is an outer lens barrel for positioning and fixing the plastic lens 4. Reference numeral 19 denotes a lens barrel for attaching and fixing the cathode ray tube 7 and the lens. These inner lens barrel 17, outer lens barrel 18, and lens mounting lens barrel 19 are an X-ray shielding plastic lens barrel that shields X-rays from emitting outside the projection lens in the structure of the X-ray shielding projection lens of the present invention. It is. This inner barrel 17
The plastic material used for the outer barrel 18 and the lens barrel 19 shields X-rays generated from the cathode ray tube 7, so it is made of materials that shield X-rays, such as lead compounds, barium compounds, strontium, titanium, and zirconate. , zinc, alloy (Pb-3n), antimony, other heavy metals, metals,
An inorganic substance, a mixture thereof, a composite substance, etc. mixed into plastic is used so as to have an X-ray attenuation rate necessary to shield the X-rays generated by the cathode ray tube.

It has a sealed structure that covers at least the entire front surface of the cathode ray tube 7 and prevents X-rays generated from the cathode ray tube 7 from leaking from the projection lens.

In the case of a video projector-television, the X-rays generated when high voltage is applied to the cathode ray tube 7 may cause some kind of malfunction, as the chassis (electrical circuit) used differs depending on the size and type of the video projector-television. The high voltage applied at this time also varies, but the design target value is usually 42 KV, but it is sufficient to consider a margin of 45 to 46 KV. The current value varies depending on the electric circuit and cathode ray tube used, but as shown in Table 1, it is 1500 μA, 2000 μA,
The amount of X-rays generated at a current value of 2500μA and a voltage of 45-46KV is 4.115.2.5.7mR/hr
The higher the current value, the greater the X-ray dose. As shown in Table 1, the X-ray attenuation rate to achieve the standard 0.5 mR/hr is 0.122000 for 1500 u A and 46 KV.
a A ・46KVte is 0.0962500 u A
・45KV Te is 0.088, and if it clears the most severe attenuation factor of 0.088, it can be used as a material for X-ray shielding lens barrels.

Under the above conditions, the present invention aims to find out what kind of X-ray shielding material should be mixed with plastic to maintain flame retardancy and
Select materials from among various materials to see if they can shield radiation.

Lead is commonly used for X-ray shielding. Therefore, lead oxide (hereinafter referred to as pbo) was mixed with plastic, and a 2500μA
The results of measuring the attenuation rate at , 45KV are as shown in Table 2. With a 10% mixture, even if the wall thickness of the lens barrel is 10mm, the attenuation rate is 0.
．． It was unlikely that it would fall below 088. Normally, when X-rays pass through a plastic lens barrel, the thickness is 3 mm at the thin end and 10 mm at the thick end. Pb02
When mixed at 0%, it can be used in areas with a wall thickness of 5.5 mm or more. In the case of a 30% Pb0 mixture, it was found that X-ray shielding was sufficient even with a wall thickness of 3.2 mm at 0.088 or less, but the flame retardancy was lost. Therefore, we mixed plastic with a material that maintains flame retardancy and has an X-ray shielding effect, and conducted flame retardant experimental tests and measured the X-ray attenuation rate. The results are shown in Table 2. Antimony trioxide (sb2O3) Barium sulfate (BaSO,) was found to be good. Other materials have lost their flame retardant properties.

Table 1 Table 2 Therefore, an antimony compound or a barium compound may be used as the lens barrel of the X-ray shielding projection lens. The structure of the lens barrel at this time must be designed depending on the type of shielding material. Figure 2 shows typical X-ray attenuation curves depending on the content of the shielding material and the thickness of the material. In terms of design, in order for the X-rays generated by the cathode ray tube to pass through the wall of the lens barrel, the wall thickness must be at least 2.9 mm, which intersects the line with the minimum X-ray attenuation rate of 0.088. Become. In the case of X-ray A in FIG. 1, this can be done by setting the diagonal passing distance of the outer lens barrel 18 to 2.9 mm or more. Further, in the case of X-ray H, the structure of the lens barrel may be designed so that the total passage distance of the two lips of the inner lens barrel 17 and the wall thicknesses of the inner and outer lens barrels is 2.9 mm or more. Further, in the case of plastic containing 30% of 5bzO,l, a minimum passing distance of 2.5 mm is sufficient.

In this way, we create X-ray attenuation curves based on the X-ray shielding materials and their content in advance, and select X-ray shielding plastic materials with appropriate attenuation curves for the amount of X-rays generated by various cathode ray tubes. All you have to do is select one, design the wall thickness of the lens barrel, and manufacture an X-ray shielding projection lens. Normally, a projection lens has a structure that uses an inner lens barrel and an outer lens barrel for focusing. Therefore, the wall thickness of the lens barrel can be secured at 5 mm or more in the passageway of the XwAH, so there is no need to worry about it, but the X119! 2.5 to 3.0ffiII in passage A
The wall thickness may be +, but the wall thickness at this location should be 5 to 6.
It is very easy to make a design of
5bzo3 and B a S
In a mixture of Oa, it varies depending on the mixing ratio of the two types, but 1
It is sufficient if it is 0% or more. Further, the upper limit of the content is desirably 50% or less in order not to significantly deteriorate the physical properties of the base plastic other than X-ray shielding. Furthermore, FIG. 2 and Table 2 are given as examples, and there are many other shielding materials, and depending on the purpose of use, various shielding materials can be incorporated into plastic and the attenuation curves measured for use.

Effects of the Invention As is clear from the above explanation, the present invention solves the problems of base plastic by manufacturing and combining a lens barrel with a glass lens and a plastic material mixed with an X-ray shielding material (particularly Sb, O, Ba5Oa). Flammability can be ensured and leakage of X-rays can be reliably prevented.

Unlike conventional lenses, there is no need to separately install expensive X-ray shielding glass elements (glass plates) or metal rings just for x#I shielding, or use iron frames or lead tape for X-ray shielding. This configuration achieves the purpose of X-ray shielding.

Therefore, the number of parts and assembly time can be reduced with a simple configuration, and a projection lens can be manufactured at low cost.

Figure 2 is a cross-sectional view of the lens, and Figure 2 is a characteristic diagram showing an example of the attenuation curve depending on the content and wall thickness of the shielding material that maintains the flame retardancy of the base plastic and has an X-ray shielding effect, Figures 3 and 4. The figure is a sectional view of a conventional projection lens.

2.4...Plastic lens, 7...
・Cathode ray tube, 9...Glass lens, I7・Old・
・Plastic inner lens barrel containing X-ray shielding material, 18...
Plastic outer barrel containing X-ray shielding material, 19...
Lens mounting barrel.

Claims (4)

[Claims] (1) An X-ray shielding projection lens installed at the front of the cathode ray tube in order to project an image projected onto the cathode ray tube; at least one lens including at least one glass element that blocks X-rays; and a lens barrel disposed in front of the cathode ray tube and around the lens, the lens barrel supporting the lens. 1. An X-ray shielding projection lens characterized in that the X-ray shielding projection lens is made of flame-retardant plastic and is mixed with a material that effectively shields X-rays emitted from the cathode ray tube. (2) covering at least the entire front surface of the cathode ray tube with a projection lens including at least one glass element incorporated by a lens barrel made of plastic mixed with a material that effectively blocks X-rays; The X-ray shielding projection lens according to claim 1, wherein the X-ray shielding projection lens has a structure that prevents X-rays generated from the cathode ray tube from leaking from the projection lens. (3) Compared to the amount of X-rays generated by the cathode ray tube, the amount of X-rays leaking from the projection lens is at least 0.5 mR/Hr.
The X-ray shielding projection lens according to claim 1, wherein the X-ray shielding material is mixed and the wall thickness of the lens barrel is set so as to have the following X-ray attenuation rate. (4) The lens barrel is made of antimony trioxide (Sb_2O_3), which is a material that effectively blocks X-rays and maintains flame retardancy.
2. The X-ray shielding projection lens according to claim 1, wherein a mixture of or at least one of barium sulfate (BaSO_4) is mixed therein. (5) The addition ratio of the X-ray shielding material is Sb_2O_3:10% or more,
or BaSO_4:20% or more, or Sb_2O
Using a plastic made of a mixture of _3 and BaSO_4 of 10% or more, with a maximum of 50% or less, the thickness of the lens barrel is made so that the X-ray attenuation rate is I/Io = 0.088 or less. The X-ray shielding projection lens according to claim 4, characterized in that the thickness is set.