AU2003206481B2

AU2003206481B2 - X-ray resistant lining system

Info

Publication number: AU2003206481B2
Application number: AU2003206481A
Authority: AU
Inventors: Gordon Frederick Disher; Michael Stuart Mcrae Greig
Original assignee: Fletcher Building Holdings Ltd
Current assignee: Fletcher Building Holdings Ltd
Priority date: 2002-02-21
Filing date: 2003-02-21
Publication date: 2008-07-31
Anticipated expiration: 2023-02-21
Also published as: EP1512153A1; AU2003206481A1; NZ517385A; WO2003071556A1; EP1512153A4

Description

WO 03/071556 PCT/NZ03/00033 X-Ray 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: WO 03/071556 PCT/NZ03/00033 2 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 Xray 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: WO 03/071556 PCT/NZ03/00033 3 placement of a lead strip of appropriate thickness approximately 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 ofl50mm 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.

WO 03/071556 PCT/NZ03/00033 4 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 SiO 2 and 5-3% by weight sodium silicate.

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

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 3542338 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 0 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 C" 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 drywall wall or ceiling lining system having a required level of X-ray transmission resistance, the system including a plurality of X-ray transmission resistant gypsum 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 drywall jointing compound including at least 30% by weight of barium sulphate.

Preferably, the X-ray transmission resistant gypsum wallboard may be lead backed gypsum wallboard.

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

Preferably, the X-ray transmission resistant wallboard may be formed by a continuous process.

Preferably, the drywall jointing compound may be provided as an air-drying ready mixed formulation holding the barium sulphate in a homogeneous mixture.

Preferably the drywall compound may include between 30% and 80% by weight barium sulphate.

Preferably, the drywall jointing compound may be provided as an air-drying type dry powder jointing compound containing between 30% and 95% barium sulphate, to which water is added prior to use.

Preferably, the dry powder jointing compound contains between 50% and 92% barium sulphate.

Preferably, the drywall jointing compound may be provided as a setting type dry k powder jointing compound containing between 25% and 75% barium sulphate, to which water is added prior to use.

Preferably, the dry powder jointing compound may contain between 50% and barium sulphate.

According to a further aspect of the present invention there is provided a method of oO 0 lining a wall or ceiling with a drywall wall or ceiling lining system having a required Iresistance to the transmission of X-rays, the said method including lining said ceiling or Swall with a plurality of sheets of X-ray resistant gypsum wallboard such that there is at least one joint or gap between an adjacent two or more of said wallboards, the method Sfurther including filling said at least one joint or gap with a drywall jointing compound including at least 30 per cent by weight of barium sulphate.

Preferably, the method may include the step of providing the drywall jointing compound as an air drying ready mix formulation holding the barium in a homogenous mixture.

Preferably, the method may include the step of providing the drywall jointing compound with between 30% and 80% by weight barium sulphate.

Preferably, the method may include providing the drywall jointing compound with between 50 per cent and 75 per cent by weight barium sulphate.

Preferably, the method may include the step of providing the drywall jointing compound as an air drying type dry powder compound containing between 30% and barium sulphate, the method further including the step of adding water to said air drying type dry powder compound before use.

Preferably, said dry powder compound may contain between 50% and 92% barium sulphate.

Preferably, the method may include providing said drywall jointing compound as a setting type dry powder jointing compound containing between 25% and 75% barium sulphate, the method further including the step of adding water to said setting type dry powder jointing compound prior to use.

Preferably, said dry powder jointing compound may contain between 50% and barium sulphate.

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.

WO 03/071556 PCT/NZ03/00033 7 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.

Ficures 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 orjointing compounds will be typically used to fill any gaps in order to provide a WO 03/071556 PCT/NZ03/00033 8 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 polymersbased 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.

WO 03/071556 PCT/NZO3/00033 9 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 percent by weight of calcium carbonate or other similar inert fillers and between 15 and 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 WO 03/071556 PCT/NZO3/00033 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 100OkVp.

Table 1.

Mass of Barium Sulphate per m of Equivalent lead thickness (mm) (approx) wallboard (kg/m 2 6 9 0.75 12 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 WO 03/071556 PCT/NZ03/00033 11 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 WO 03/071556 PCT/NZ03/00033 12 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

2. The wall or ceiling lining system of claim 1 wherein the X-ray transmission 10 resistant gypsum wallboard is paper faced gypsum wallboard. (Ni
3. The wall or ceiling lining system of claim 2 wherein the X-ray transmission resistant gypsum wallboard is formed by a continuous process.
4. The wall or ceiling lining system of claim 1, 2 or 3 wherein the drywall jointing compound is provided as an air-drying ready mixed formulation holding the barium sulphate in a homogenous mixture. The wall or ceiling lining system of claim 4 wherein the drywall jointing compound contains between 30% and 80% by weight barium sulphate.
6. The wall or ceiling lining system of claim 5 wherein the drywall jointing compound contains between 50 and 75% by weight barium sulphate.
7. The wall or ceiling lining system of any one of claims 1 to 3 wherein the drywall jointing compound is provided as an air-drying type dry powder jointing compound containing between 30% and 95% barium sulphate, to which water is added prior to use.
8. The wall or ceiling lining system of claim 7 wherein the dry powder jointing compound contains between 50% and 92% barium sulphate.
9. The wall or ceiling lining system of any one of claims 1 to 8 wherein the drywall jointing compound is provided as a setting type dry powder jointing compound containing between 25% and 75% barium sulphate, to which water is added prior to use. The wall or ceiling lining system of claim 9 wherein the dry powder jointing compound contains between 50% and 70% barium sulphate.
11. A method of lining a wall or ceiling with a drywall 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 resistant gypsum wallboard such that there is at least one joint or gap between an adjacent two or more of said 00 0 -14- wallboards, the method further including filling said at least one joint or gap with a drywall Sjointing compound including at least 30% by weight of barium sulphate.
12. The method of claim 11 including the step of providing the drywall jointing compound as an air-drying ready mixed formulation holding the barium sulphate in a homogenous mixture. 00 13. The method of claim 12 including the step of providing the drywall jointing Scompound with between 30% and 80% by weight barium sulphate. t 14. The method of claim 13 wherein the drywall jointing compound contains between and 75% by weight barium sulphate.
15. The method of claim 11 including the step of providing said drywall jointing compound as an air drying type dry powder compound containing between 30% and barium sulphate, the method further including the step of adding water to said air drying type dry powder compound before use.
16. The method of claim 15 wherein said dry powder compound contains between 50% and 92% barium sulphate.
17. The method of claim 11 including providing said drywall jointing compound as a setting type dry powderjointing compound containing between 25% and 75% barium sulphate, the method further including the step of adding water to said setting type dry powder jointing compound prior to use.
18. The method of claim 17 wherein said dry powder jointing compound contains between 50% and 70% barium sulphate.
19. A drywall 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.