EP1512153A1

EP1512153A1 - X-ray resistant lining system

Info

Publication number: EP1512153A1
Application number: EP03705560A
Authority: EP
Inventors: Michael Stuart Mcrae Greig; Gordon Frederick Disher
Original assignee: Fletcher Building Holdings Ltd
Current assignee: Fletcher Building Holdings Ltd
Priority date: 2002-02-21
Filing date: 2003-02-21
Publication date: 2005-03-09
Also published as: AU2003206481B2; AU2003206481A1; WO2003071556A1; EP1512153A4; NZ517385A

Abstract

A wall or ceiling lining system with a required level of X-ray transmission resistance includes a plurality of X-ray transmission resistant wallboards (2, 3) with at least one joint (4) or gap between an adjacent two or more of said X-ray transmission resistant wallboards. Each of the joints or gaps is provided with a wallboard jointing material (8) including at least 30 per cent by weight of barium sulphate or an equivalent. A method of lining a wall or ceiling with a wall or ceiling lining system having a required level of resistance to the transmission of X-rays is also disclosed.

Description

X-Rav Resistant Lining System Technical Field

The present invention relates to improvements in and relating to X-ray barriers, and in particular to a system including a wallboard and complimentary wallboard jointing compound which provides a required level of X-ray transmission resistance.

Background Art

For the purposes of this specification, X-rays are defined as the spectrum of electromagnetic radiation with a wavelength shorter than that of visible light and which exhibit a high level of penetration and are suitable of use in internal imaging of humans.

In many situations, particularly in the industrial and health sectors, X-ray machines or CAT scan machines of various types, are required to be operated and in situations where during operation the human operators, or observers or occupants of adjacent rooms, have a risk of exposure to the X-rays.

As is well recognised in medical literature, exposure of a human being to X-rays above a threshold level over any prolonged period can be detrimental to health and in particular in respect of an enhanced risk of cancer.

Typically the X-ray machines or the like, will be situated in a room dedicated for this purpose and it is well recognised that the walls, ceilings and floors in such rooms need to be resistant to the transmission of X-rays in order to ensure that the occupants of adjacent rooms or spaces are not subjected to unacceptable levels/doses of the X-rays.

In specifying a resistance to the transmission of X-rays this is typically measured in relation to lead of varying thickness equivalents, the most common, at least in New

Zealand, being lead equivalents of 1 millimetre and 2 millimetres.

To the present time various proposals have been put forward to achieve this X-ray resistance in wall and ceiling structures, in particular: (i) Lining the framed walls or ceilings with a sheet type building material which has an appropriate thickness of lead sheet adhered to the back of the sheet;

(ii) solid plastering the walls and/or ceilings with a gypsum plaster to which barium sulphate has been added;

(iii) lining the framed walls and/or ceilings with sheets of glass fibre reinforced gypsum to which barium sulphate has been added;

(iv) lining the walls with sheets of paper faced machine manufactured gypsum wallboard (ASTM C 36, C 1396) which has been manufactured to contain a proportion of barium sulphate.

In the above proposals, barium sulphate has been identified as a preferred X-ray transmission resistant substance or compound and it will be referred to later in this context. However, it will be appreciated that other substances or compounds having an equivalent or better blocking effect may be available, or become available, and such are intended to be included within this specification as alternatives to barium sulphate as appropriate. Appropriate barium sulphate equivalents may include other heavy metal salts, such as lead or uranium, or the actual metal particles. From a health and safety point of view barium sulphate, the material used in barium meals, is the safest and most cost effective.

At present barium sulphate is the only cost effective heavy metal salt, but this may change in the future. If cost effective, lead particles could also be used.

In the above proposals it is, of course, important that the walls are completely X- ray secure up to the specified lead equivalent and up to a specified height. However, even where two boards of specified lead equivalence are very tightly butted together, the

X-rays will be able to penetrate even small gaps between the sheets and thus reducing the X-ray security of the room.

In recognising this problem various solutions have been proposed where sheet type X-ray transmission resistant materials are being used, (there being no equivalent problem with a solid plaster wall if a uniform thickness is maintained), namely: (i) placement of a lead strip of appropriate thickness approximately 50 millimetres wide, the full length of the framing behind the intersection of the sheets;

(ii) in the use of paper faced X-ray transmission resistant gypsum wallboard, in either a 1 or 2 layer system, the placement of a 50 millimetre wide strip of the same thickness board the full length of the framing member where the two boards are joined.

The above proposals all suffer to some extent from problems relating to effectiveness, complexity, lead related health issues and/or cost.

Throughout most of the world the standard form of construction, including in most hospitals, is Drywall. This consists of a vertical framing of steel or timber studs. Sheets of paper faced gypsum plasterboard manufactured worldwide on special high speed machines, are fixed to these studs with screws or nails and adhesive. The board has a recess [or taper] on the two long edges.

When assembled, the recess is filled with three coats of a gypsum setting compound or a calcium carbonate based air drying compound or a combination of the two types of jointing compound. A paper or fibre glass mesh tape is commonly inserted in the recess [ embedded in the jointing compound] to reinforce the joint. The recess is overfilled with jointing compound and flushed out to a width of 150mm or more on either side of the joint. The compound when dry is lightly sanded to provide a smooth surface which after decoration with paint or a paper or vinyl lining, presents a continuous surface with no signs of the joints.

The sheets of plasterboard currently used produce a readily assembled system that may also provide, fire, sound and moisture protection. However, plasterboard as currently manufactured and assembled provides virtually no x-ray protection. The benefits of the current system are that plasterboard is manufactured and jointed in the normal fashion, but also provides X-ray resistance.

Examples of related publications in the area include the following. Derwent Abstract No.60786 E/29 "Radiation shield filling material - comprising natural, synthetic, or silicone rubber, heavy metal (cpd) and neutron absorber "(Japanese Patent number 57-096296 A) relates to a silicon based flexible filling material which contains barium sulphate in order to provide a radiation shielding effect.

A feature of the sealant is that it is able to elastically deform while still providing a required radiation shielding performance.

One problem with such a substance is that it may be unsuitable for use as a jointing compound for use between adjacent sheets of X-ray transmission resistant wallboard. The flexible nature of the compound may mean that it is not easily trowelled or sanded, meaning that it is difficult to provide the smooth monolithic surface normally achieved with gypsum based wallboard systems.

European Patent number 125889 A "Radiation shielding putty-like composition" relates to a putty which has a radiation shielding effect.

The putty uses barium in the form of a metal soap as a thickener rather than to provide an X-ray shielding effect. An inorganic binder with a density of not less than 5 is used to provide the radiation shielding.

This putty may also be difficult to sand or trowel and so may not be suitable for use as a wallboard jointing compound.

US 4437013 "Neutron and Gamma Radiation Shielding Material, Structure, and process of making a structure", describes a shielding material consisting of 95-97% by weight SiO₂ and 5-3% by weight sodium silicate.

The material is suitable for shielding against neutrons and gamma rays but not X- rays.

Derwent Abstract No 87-077443/11 "Shielding piping passage of a wall or floor - comprises fitting a burying sleeve in to a thru-hole of the wall or floor, passing a piping covered with a corrugated plate thru the sleeve and packing Pb hair in the gap between sleeve and piping" (JP 064273) relates to a method of neutron shielding which involves filling gaps with lead. German patent number 3542668 relates to a flexible silicon rubber compound which is not suitable for use as a wallboard jointing compound for the reasons cited above with relation to Derwent Abstract No.60786 E/29.

The Applicant does not concede that any or all of the patents and abstracts referred to above necessarily form part of the common general knowledge of a skilled addressee, or are necessarily patents or abstracts which would be discovered by a diligent searcher.

Object of the Invention

It is an object of the present invention in to provide a wall or ceiling lining system having a required level of X-ray transmission resistance and/or method of lining a wall or ceiling with a wall or ceiling lining system having a required resistance to the transmission of X-rays which will overcome, or at least ameliorate, problems with existing systems and/or methods, or which at least will provide the public with a useful choice.

Further objects will become apparent from the following description. Summary of the Invention

According to one aspect of the present invention there is provided a wall or ceiling lining system having a required level of X-ray transmission resistance, the system including a plurality of X-ray transmission resistant wallboards wherein at least one joint or gap between an adjacent two or more of said X-ray transmission resistant wallboards is provided with a wallboard jointing material including at least 30 per cent by weight of barium sulphate or an equivalent.

Preferably, the X-ray transmission resistant wallboard may be paper faced gypsum wallboard.

Preferably, the X-ray transmission resistant wallboard may be formed by a continuous process. Preferably, the wallboard jointing material may be provided as a ready to use paste air-drying compound holding the barium sulphate in a homogenous mixture.

Preferably, the wallboard jointing material may be provided as a dry powder premixed with spray dried synthetic binders

Preferably, the wallboard jointing material may include between 30 per cent and 80 per cent by weight barium sulphate or equivalent in the ready to use paste.

Preferably the wallboard jointing material may include between 50 per cent and 75 per cent by weight barium sulphate in the ready to use paste.

According to a further aspect of the present invention there is provided a method of lining a wall or ceiling with a wall or ceiling lining system having a required resistance to the transmission of X-rays, the said method including lining said ceiling or wall with a plurality of sheets of X-ray ray resistant wallboard such that there is at least one joint or gap between an adjacent two or more of said wallboards, the method further including filling said at least one joint or gap with a jointing material including at least 30 per cent by weight of barium sulphate or an equivalent.

Preferably, the method may include providing the wallboard jointing material as a ready to use paste air-drying compound holding the barium sulphate or equivalent in a homogenous mixture.

Preferably, the method may include providing the wallboard jointing material with between 30 per cent and 80 per cent by weight barium sulphate or equivalent in the ready to use paste.

Preferably, the method may include providing the wallboard jointing material with between 50 per cent and 75 per cent by weight barium sulphate in the ready to use paste.

According to a further aspect of the present invention a wall or ceiling lining system having a required resistance to the transmission of X-rays is substantially as herein described with reference to any one of Figure 2, Figure 4, Figure 5a, 5b or 5c or Figure 6a, 6b or 6c. Further aspects of this invention which should be considered in all its novel aspects will become apparent from the following description given by way of example and with reference to the accompanying drawings.

Brief Description of the Drawings

Figure 1 : Shows a wall lining fastened to a wooden stud prior to the application of a wallboard jointing compound.

Figure 2: Shows the wall lining of Figure 1 provided with a jointing compound according to a preferred embodiment of the present invention.

Figure 3: Shows a similar wall lining system to Figure 1 mounted to a metal stud.

Figure 4: Shows the wall lining of Figure 3 provided with a jointing compound according to a preferred embodiment of the present invention.

Figures 5a-c and 6a-c: Show very diagrammatically plan cross-sectional views of rooms featuring joint and gap material according to one possible embodiment of the invention.

Brief Description of Possible Embodiments

As mentioned above, in providing the wall or ceiling system for a room which requires a particular level of X-ray transmission resistance, any joint or gaps in the wall or ceiling lining system provide an avenue for the penetration through the wall system of the X-rays and into adjoining rooms or spaces.

In the construction of a gypsum wallboard based wall or ceiling (also termed a dry wall) joint or jointing compounds will be typically used to fill any gaps in order to provide a δ seamless wall for the purpose of providing an attractive decorative finish.

An important factor in providing such a finish is the jointing compounds ability to be trowelled into the gaps in the wallboard, and to be sanded to a smooth finish after setting or drying.

Paper or fibreglass reinforcing tape is typically embedded in the jointing compounds in order to reduce the likelihood of the joint cracking with any movements of the underlying structure.

Typically in New Zealand and Australia, the joint compounds used for embedding of the reinforcing tapes will be of a setting type based on gypsum plaster (which is mixed with water prior to use) or an air drying type joint compound (either as a premixed ready to use paste or a premixed powder which is mixed with water prior to use) utilising a calcium carbonate filler together with a synthetic polymeric type binder. Setting type compounds are typically utilised for first and second coats of compound in the jointing process (not for the finishing or top coats) whereas air drying joint compounds may be formulated as either taping compounds and/or finishing or topping compounds.

Typically air drying joint compounds may include:

1. An inert filler, usually a finely ground calcium carbonate such as calcite or limestone, but which may include portions of fillers such as perlite and/or mica to impart additional properties such as light weight and crack resistance.

2. A binder which may include but is not limited to styrene-butadiene copolymers, polyvinyl acetates and polymers. based on acrylic monomers as either an emulsion or a dry powder and may include polymeric materials of natural origin such as a starch or casein.

3. Modified celluloses and clays to provide thickening and appropriate rheological properties.

4. Fungicides which may be designed to protect the joint compound from fungal and bacterial attack both before and after use. 5. Water in order to achieve a desired viscosity.

6. Small quantities of other additives in order to modify trowelling, drying and other properties.

Typically an air drying ready mix joint compound may contain between 60 and 80 percent by weight of calcium carbonate or other similar inert fillers and between 15 and 25 percent by weight of water.

In one embodiment, the system of the present invention includes a wallboard joint compound which has been formulated to provide an air drying ready mixed formulation including between 30 and 80 percent by weight of a barium sulphate (or an equivalent as herein defined), and preferably between 50 and 75 percent of that material. Preferably the barium sulphate may be dispersed homogeneously throughout the compound in order to ensure that the level of resistance to X-ray transmission is consistent.

In an alternative formulation the air dried joint compound of the present invention may be provided as a dry powder premixed with spray dried synthetic binders and between 30 and 95 percent by weight of barium sulphate, and preferably between 50 and 93 percent of that material, to which water is added and mixed prior to application to the joint, gap or fastener head.

In an alternative formulation in a dry powder setting type joint compound the present invention may provide between 25 and 75 percent by weight of barium sulphate and preferably between 50 and 70 percent with hydraulic binders including but not confined to gypsum plaster.

Gypsum wallboard is conventionally manufactured by enclosing a core containing an aqueous slurry of calcined gypsum (stucco or calcium sulphate hemihydrate) between two sheets of paper under high speed continuous conditions. Typically the longitudinal edges of the face paper are wrapped to contain the slurry. A recess or taper is typically incorporated on the face side of each of the longitudinal edges of the gypsum wallboard to facilitate the wallboard jointing operation.

Gypsum wallboard with X-ray transmission resistance is manufactured in a conventional manner with the addition of sufficient barium sulphate to provide the required X-ray resistance. The ratio of barium sulphate to stucco may be easily varied to provide a wide range of X-ray transmission resistant performance.

X-ray transmission resistant gypsum wallboards typically have a stucco to barium sulphate ratio of between 0.3 and 0.7. The effectiveness of these X-ray transmission resistant gypsum wallboards as a component in an X-ray barrier system is expressed as equivalent to a specific thickness of lead sheeting when measured at a specific X-ray intensity. A typical X-ray intensity for these tests would be 100 kVp.

Table 1 shows the results of the Applicant's tests regarding the relationship of lead equivalent and mass of barium sulphate per unit area of 13mm thick wallboard at an X-ray intensity of 100kVp.

Table t

The equivalent lead thickness will increase proportionally with increased barium sulphate weight per square metre, which can be increased by increasing board thickness, or increasing number of layers of board.

In a preferred embodiment, the jointing compound may contain 72.8% barium sulphate by weight in the readymix compound.

A joint compound with a high level of barium sulphate, such as 72%.8 by weight in the wet or ready to use compound, may, when dried, contain 1.8kg per square metre of barium sulphate per millimetre of dried thickness in the joint. By comparison, a 13mm wallboard might have just 0.75 kg of barium sulphate per square metre per mm of board thickness.

Those skilled in the art will therefore appreciate that the jointing compound of the present invention provides a relatively greater X-ray transmission resistance than the wallboard. In addition, in some cases the flow of joint compound into the gap between adjacent boards may result in some jointing compound flowing behind the board and further increasing the X-ray transmission resistance.

It may be desirable to leave a small gap between the edges of the X-ray transmission resistant wallboards to allow for penetration of the X-ray transmission resistant jointing compound between and/or behind the sheet edges. A further embodiment would be to generate machine made edges on the X-ray transmission resistant wallboards with a rounded profile to enhance penetration of the X-ray transmission resistant jointing compound into the joint. Alternatively the machine made edge of the X-ray transmission resistant wallboard may be 'lightly buttered' with the joint compound prior to fastening to the framing.

Referring to the accompanying drawings, Figure 1 shows very diagrammatically a cross section through part of a wall system of a room which is required to provide a specified resistance to X-ray transmission.

The wall system 1 is shown including a pair of abutting X-ray transmission resistant gypsum wallboards 2, 3 which although butted tightly edge to edge is still likely to create a gap along the adjacent edges indicated by arrow 4. The wallboards 2, 3 which will provide X-ray resistance to the required level, are shown secured to a vertical wooden stud 5 behind which is the wallboard 6 of an adjacent room or space.

In Figure 2 a joint is shown provided between the boards 2, 3 and utilising a jointing compound 8. Depending on whether it is an air drying ready mix joint compound or a dry powder setting compound this may preferably contain between 30 and 80 percent of barium sulphate or an equivalent, although the percentage may be lower or higher.

The boards 2, 3 will also provide X-ray transmission resistance of a suitable level but unlike the jointing compound 8 will be typically composed of a gypsum to barium sulphate ratio of between 0.3 and 0.7.

Referring to Figures 3 and 4, the same reference numerals have been used as in

Figures 1 and 2 where appropriate. However, in this embodiment wooden stud 5 is shown replaced by a metal stud 7.

Referring now to Figures 5a-c and 6 a-c, again with the alternative use of metal or wooden studs 7, 5, diagrammatic cross sectional views across a wall system for a room are shown. The jointing compound is shown provided in joints along the wall faces and joints 8A in the wall corners. Figures 5a, 5b, 6a and 6b show the overlapping joints preferred when two or more layers of X-ray transmission resistant wallboard 2, 9 are used.

Any fasteners in the field of face of the X-ray transmission resistant gypsum wallboard will require application of a coat of X-ray transmission resistant jointing compound.

In experimental tests the present invention has been shown to provide a required X-ray transmission resistance for a wall lining system despite the existence of joints or gaps in the wall system which would previously have affected the X-ray resistance capability of the wall lining system.

Those skilled in the art will appreciate that the present invention provides a wall or ceiling lining system which may be provide most or all of the benefits of a standard gypsum wallboard interior cladding (or drywall) while also providing a required level of resistance to transmission of X-rays.

Where in the foregoing description reference has been made to specific components or integers of the invention having known equivalents then such equivalents are herein incorporated as if individually set forth.

Although this invention has been described by way of example and with reference to possible embodiments thereof, it is to be understood that modifications or improvements may be made thereto without departing from the scope of the appended claims.

Claims

Claims:

1. A wall or ceiling lining system having a required level of X-ray transmission resistance, the system including a plurality of X-ray transmission resistant wallboards wherein at least one joint or gap between an adjacent two or more of said X-ray transmission resistant wallboards is provided with a wallboard jointing material including at least 30 per cent by weight of barium sulphate or an equivalent.

2. The wall or ceiling lining system of claim 1 wherein the X-ray transmission resistant wallboard is paper faced gypsum wallboard.

3. The wall or ceiling lining system of claim 1 or 2 wherein the X-ray transmission resistant wallboard is formed by a continuous process.

4. The wall or ceiling lining system of claim 1 , 2 or 3 wherein the wallboard jointing material is provided as a ready to use paste air-drying compound holding the barium sulphate in a homogenous mixture.

5. The wall or ceiling lining system of any one of the previous claims wherein the wallboard jointing material includes between 30 per cent and 80 per cent by weight barium sulphate or equivalent in the ready to use paste.

6. The. wall or ceiling lining system of any one of claims 1 to 4 wherein the wallboard jointing material includes between 50 per cent and 75 per cent by weight barium sulphate in the ready to use paste.

7. A method of lining a wall or ceiling with a wall or ceiling lining system having a required resistance to the transmission of X-rays, the said method including lining said ceiling or wall with a plurality of sheets of X-ray ray resistant wallboard such that there is at least one joint or gap between an adjacent two or more of said wallboards, the method further including filling said at least one joint or gap with a jointing material including at least 30 per cent by weight of barium sulphate or an equivalent.

8. The method of claim 7 including the step of providing the wallboard jointing material as a ready to use paste air-drying compound holding the barium sulphate or equivalent in a homogenous mixture.

The method of claim 7 or 8 including the step of providing the wallboard jointing material with between 30 per cent and 80 per cent by weight barium sulphate or equivalent.

The method of claim 7 or 8 including the step of providing the wallboard jointing material with between 50 per cent and 75 per cent by weight barium sulphate or equivalent.

A wall or ceiling lining system having a required resistance to the transmission of X-rays substantially as herein described with reference to any one of Figure 2, Figure 4, Figure 5a, Figure 5b, Figure 5c, Figure 6a, Figure 6b or Figure 6c.