Field of Invention

This invention relates to sheeting, in particular, to sheeting for use in contamination control situations.

Background to the Invention

Maintaining a controlled environment is essential in many academic, industrial and medical settings, and controlling contamination entering that environment is very important. For example, many hospitals, factories, food preparation areas, spray-paint booths and laboratories utilise a controlled environment, which may be referred to as a cleanroom. Precautions are taken such as subjecting cleanroom staff to strict clothing regulations and using a gowning room where the staff can change clothes under "controlled" conditions so as to prevent any particulates from entering from the outside environment. Certain areas in a cleanroom may have more stringent measures than others, with packaging areas, corridors, gowning rooms and transfer hatches being incorporated to maintain strict contamination control measures.

In hospitals, cleanroom precautions can be used to try to reduce the incidence of infectious diseases spreading. In industry, particularly in the pharmaceutical, electronics, aerospace, catering, automotive, biomedical, IT, nuclear, optical and medical devices industries, it is often essential to ensure that products are free from contamination. Contamination of a controlled environment poses a threat to product processes, the consequences of which are lower product yields, raised costs and decreased profits.

Contaminants are particles that enter an environment where they may potentially have a negative effect. There are many types of contaminants and they can have a wide variety of effects on different environments. Contaminants can be bacteria or other organisms that are potentially harmful to their surroundings. More familiar contaminants can be things such as dust and dirt. Contaminants can be carried on any surface entering a controlled environment, or in the air. Particles can be suspended in the air for hours where they undergo rapid proliferation, contaminating the surrounding environment. Once there is no movement and turbulence stops, airborne contaminants fall. If they fall onto a surface such as an unprotected floor they may rise again and be redistributed into the air as a result of the vortices created by the movement of personnel and wheeled traffic.

Studies have shown that contamination enters a controlled environment through entrances and exits, mostly at or near floor level. As a result of this, attempts have been made to reduce the contamination entering a controlled environment by using particular floor coverings.

It is known to use particular floor coverings in entry and exit areas to controlled environments to attract, collect and retain foot and wheel borne contaminants, thereby reducing the contamination entering the controlled environment.

One type of flooring, known as polymeric matting, is particularly effective in certain situations in controlling particulate contamination. It is semi-permanently installed and can be cleaned as required. Dycem's Protectamat flooring system is an example of this. The polymeric matting comprises a single layer of polymer, usually a specially blended polymer formulation comprising polyester plasticisers leading to a tack that can attract and bind contaminants. This is typically at least 7mm thick, to provide sufficient strength and weight to resist tearing or crumpling as traffic moves over the matting. However, this thickness makes the matting hard to manoeuvre. As noted above, this is a semi-permanent or permanent solution, in that the polymeric matting is particularly long-lasting and can be used for 3-5 years before replacement. This works very well when long term contamination control is required and the operator has sufficient resources to invest in such a system. However, it is less suitable for a situation where contamination control flooring is needed for a short period or at a low cost, for example, a testing laboratory, where testing is going on for a few days or for a few weeks, or temporary control over a contamination zone such as during asbestos removal. "Peel off mats, also known as adhesive floor mats or tacky mats, are also used in contamination control situations particularly where the need for contamination control is short lived, or if there is not enough resource to fund installation of permanent contamination control flooring. These mats comprise a laminate of thin (0.1 to 0.2 mm) synthetic material layers, typically thirty layers, which are stuck together by a pressure sensitive adhesive to form a mat which is several millimetres thick. The mat is then placed on a floor to capture contaminants, for example, from feet or the wheels of trolleys. In use, the upper layer of a mat is removed from the base on a regular basis, exposing a new clean layer.

These "peel off mats have several disadvantages. Firstly, and most importantly, the peel off mats do not work very well in comparison to polymeric matting. The surface tack degrades immediately after initial contact and does not retain nearly as many contaminants. Second, adhesive can be removed from the uppermost layer to adjacent floor surfaces by feet and wheels which can itself attract contaminants, meaning that peel off mats can be counterproductive by actually encouraging contaminants into the controlled area. Third, when an upper layer is removed from the mat it creates a considerable volume of waste which is difficult to recycle. Fourth, when removing an upper layer, contaminate particles can be released which may be hazardous to a user who may breath them in. Fifth, as layers are removed, the mat becomes progressively weaker.

It is an object of the invention to overcome, or at least to mitigate, the disadvantages of prior art products.

Summary of the Invention

According to a first aspect, the invention provides a contamination control sheet comprising: a support layer which is coated on a top surface with a polymeric contamination control layer; wherein the support layer comprises a polymer, is 0.1 mm to 1 mm thick, and the bottom surface of the support layer is coated with an adhesive; and wherein the polymeric contamination control layer is 0.1 mm to 2.5 mm thick, and is transparent or translucent, so that the top surface of the support layer is visible through the polymeric contamination control layer.

By using a polymeric support layer coated on a top surface with a polymeric contamination control layer, the invention provides a sheet with the contamination control of a polymeric mat but in a much thinner and more easily handled format. In contrast to the 7 mm thick polymer mats of the prior art, the present invention can provide a functioning contamination control sheet with a thickness of about 0.2 mm to about 3.5 mm. By reducing the amount of polymer required the sheet is less expensive to manufacture. The reduced weight and increased flexibility of a thinner material also benefit packing, transport and installation operations. Owing to the thinness of the sheet, the strength and weight to resist tearing or crumpling is reduced. However, use of the adhesive overcomes this and makes use of the thinner sheet possible. By having the bottom surface of the support layer adhered to a surface, the strength of the surface is employed to help prevent tearing or crumpling of the sheet. The present invention therefore provides a sheet that can be conveniently used as a temporary installation, avoiding the waste generated by a peel off sheet typically used in this situation. The sheet can be rapidly and easily installed. The sheet is also economical and may be treated as disposable, one-use contamination control sheeting.

This sheeting is light in weight and held firmly in place by the adhesive. It can therefore be used on vertical surfaces, such as walls and doors, as well as horizontal surfaces such as floors and worktops. The sheeting can be used as a mat for flooring.

Furthermore, as the appearance of the top of the sheet is different from the bottom, a visual cue is provided to help prevent installation of the sheet in an upside down configuration.

The polymeric contamination control layer can be 0.2 mm to 0.7 mm thick.

The polymeric contamination control layer can comprise a blend of polymer and polyester plasticisers. This allows the polymeric contamination control layer to have appropriate flexibility and contamination control properties. The polymeric contamination control layer can comprise at least one anti-static additive.

The contamination control can operate simply by trapping contaminants such as microbes. In addition, the polymeric contamination control layer may comprise at least one antimicrobial agent to actively kill microbes that contact the mat. The antimicrobial agent may be silver nitrate.

Printing may be desired, for example, to provide a border that guides users over the contamination control area. However, any printing on the top of the mat would be exposed to traffic and cleaning operations that could lead to damage. Printing on a contamination control polymeric layer may also interfere with contamination control properties. Equally, contamination control substances may interfere with the stability of the printed ink. In the past, printed material has been presented on edging strips to the contamination control area rather than on the contamination control area itself.

In a preferred embodiment of the present invention, it is the top surface of the support layer that is printed and not the polymeric contamination control layer or a separate edging strip. The printing would be visible through a transparent or translucent polymeric contamination control layer. The invention provides a way of displaying printing that is protected, but without sacrificing the thinness of the contamination control sheet. This is because the contamination control surface provides three discrete functions: a) contamination control; b) protection of printing on the top surface of the support layer; and c) visibility of printing on the top surface of the support layer.

The whole top surface of the support layer may be printed. This may assist with adhesion of the polymeric contamination control layer.

The top surface of the support layer may have a printed border. The border may outline the contamination control zone such that users are directed to use the contamination control zone. Optionally, the entire top surface of the support layer may be printed. For example, the entire top surface could be printed with a single colour, which would provide the colour of the contamination control sheet in general. This would be in contrast to tinting the support layer or contamination control layer polymers. The top surface could also be printed with a single background colour and also letters, numbers, words, phrases, patterns, images, or combinations thereof in different colours.

The top surface of the support layer may have printing on it that comprises an ink that is cured using ultraviolet (UV) light. UV curable inks such as Oce IJC258 manufactured by Canon work particularly well. Such inks are cured without bleeding of the ink occurring. The printed surface is where two layers join. UV curable inks are particularly good at preventing delamination of the two layers in the region of the UV curable ink.

Usually, the contamination control sheet would consist of the support layer and the polymeric contamination control layer with a release liner often used to cover the adhesive. However, it is possible to have further layers. At least one layer may be interposed between the support layer and the polymeric contamination control layer. Such a layer must also allow the support layer to be visible. An interposed layer may provide features such as further support or further contamination control properties. The bottom face of the support layer may also be coated with a further layer, for example an insulating layer, grip layer or layer that further distinguishes the top of the sheet from the bottom.

According to a second aspect, the invention provides a method of providing contamination control, the method comprising deploying a contamination control sheet according to the first aspect of the invention in an environment where contamination is to be controlled, by adhering the exposed adhesive layer to a surface in the environment where contamination is to be controlled. Where a release liner is present, this is first removed.

According to a third aspect, the invention provides a method of making a contamination control sheet according to the first aspect of the invention, the method comprising the steps of a) providing a support layer comprising a polymeric layer which is coated on a bottom surface with an adhesive, wherein the adhesive is covered by a release liner, and b) coating a top surface of the support layer with a transparent or translucent polymeric contamination control layer. The method may also comprise the step of printing the top surface of the support layer before step b). The top surface may be coated with a liquid polymer precursor and the liquid polymer precursor cured. Curing may be done using methods well known in the art, such as by heating.

Brief Description of the Drawings

The invention will now be described by way of example only with reference to the accompanying drawing, Figure 1, which is a schematic view of a sheet that is an embodiment of the invention.

Description

The invention provides a contamination control sheet comprising a support layer which is coated on a top surface with a polymeric contamination control layer. By support, we mean that the layer generally assists with providing strength to the sheet in this case by being able to adhere to supportive surfaces in addition to through its inherent strength. Suitable supportive surfaces include floors, door panels and walls.

The support layer has a top surface. By top surface, we are referring to one of the two opposing large surfaces of the support layer. The top surface is coated with a polymeric contamination control layer. By this, we mean that the area of the top surface of the support layer is substantially covered with a polymeric contamination control layer.

The polymeric contamination control layer is transparent or translucent. By this, we mean that the polymeric contamination control layer is sufficiently transparent or translucent that the top surface of the support layer is visible through the contamination control layer. The contamination control layer may be coloured, or tinted, as long as the transparency or translucency properties of the layer are preserved. By stating that the top surface is visible through the polymeric contamination control layer, we mean that the top surface is also visible through any other layers interposed between the polymeric contamination control layer and the printing.

The bottom surface of the support layer is coated with an adhesive. Any suitable adhesive can be used. The adhesive should cover the majority of the bottom surface of the support layer so that the majority of the area of the support layer is held against the surface it is adhered to. This is in contrast, for example, to using strips of double- sided adhesive tape. Such a method would not provide such a durable solution as tears or crumples could readily propagate through sections of the sheeting not adhered to a surface.

The adhesive is usually covered by a release liner. Release liners are well known and typically comprise a plastic, silicone or waxed paper sheet. Release liners are commonly used on items such as stickers and plasters to prevent the adhesive layer from prematurely adhering to a surface or becoming denatured by binding unwanted matter such as dust. The release liner is usually removed just prior to use, and separates to expose the layer of adhesive without taking any adhesive material with it. The adhesive layer is then stuck to the intended surface.

The support layer is 0.1 mm to 1 mm thick and the polymeric contamination control layer is 0.1 mm to 2.5 mm thick. The support layer may optionally be 0.2 mm to 1 mm thick or may optionally be about 0.5 mm thick. The contamination control layer may optionally be about 0.5 mm to 2 mm thick, or may optionally be about 0.8 mm to 1.8 mm thick.

Contamination control materials are known in the art and are used to protect controlled environments. They attract and retain contaminants by having a high surface tack. In other words, particulate contaminants such as dust, spores or bacteria will adhere to the polymeric contamination control layer due to its high surface tack. The high surface tack of the polymeric contamination control layer is provided by a high coefficient of friction, for example, the coefficient of friction may be at least 1.5μ or at least 2μ or at least 2.5μ. Preferably the coefficient of friction of the polymeric contamination control layer is about 3μ or about 3.5μ. The coefficient of friction may be the dynamic coefficient of friction. Methods for determining the coefficient of friction will be familiar to the skilled person and may be as described in BS EN 13893 :2002.

The polymeric contamination control layer may comprise a blend of polymer and polyester plasticisers. The plasticiser contributes to the high surface tack of polymeric control layer. Suitable materials are known to those skilled in the art and are described in GB 1399191, GB1475366 and GB2025319(A). Transparent and translucent polymers and plasticisers for use with these polymers are well known to those skilled in the art.

The support layer may comprise a single colour. Generally, the support layer will not be transparent or translucent and will be of a colour that provides a good contrast to any printed material and/or the polymeric contamination control layer. For example, the support layer may be white and the printing black.

The contamination control sheet usually has two layers. However, in a different embodiment, at least one layer may be interposed between the support layer and the polymeric contamination control layer. Any interposed layers must allow the support layer to be visible through the polymeric contamination control layer. Further layers may also be interposed between the support layer and the adhesive. For example, a further layer may help to hold the adhesive to the sheet.

The polymeric contamination control layer may comprise at least one anti-static additive. Such additives are well-known to those skilled in the art.

The contamination control sheet may comprise an antimicrobial agent. By this, we mean an agent with antibacterial or antifungal properties. Such agents are well known. One example is silver nitrate. Other silver compounds or metallic silver can also be used. The antimicrobial agent can be included at a level of between 0.05% and 5% by weight of the polymeric contamination control layer. It preferably comprises between 0.05% and 1% by weight of the polymeric contamination control layer, more preferably 0.05% to 0.2%, or around 0.1% by weight of the polymeric contamination control layer. One example of a commercially available antimicrobial agent suitable for inclusion in the contamination control sheets is Biomaster 999.

The support layer may comprise a print receptive polymer substrate. By this, we mean that the polymer should be able to bind with at least one type of ink such that once the ink has dried it is not easily smudged.

The top surface may be printed. In other words, the top surface may have printing on it. The printing may have been performed by any standard automated printing apparatus or by hand. An ink that is compatible with the polymer layers should be used for the printing. The printing may be of a letter, number, word, phrase, pattern, image, or combination thereof. The printing may be of any colour, however, a colour that is in contrast to the colour of the support layer would assist with visibility. The entire area of the top surface may be printed, for example, with a single colour.

The top surface of the support layer may be printed with a border. The border is a strip that runs around the outer edges of the sheet to mark the border of the contamination control zone. The border may be a solid colour, a pattern, an image or combination thereof. The printing may provide other information, such as a logo or safety warning.

Examples of printable polymer layers with printing on one side and an adhesive and a release liner on the other side are known. An example is the Orafol (RTM) Orajet (RTM) film, typically used for sticking decorative or advertising images to the bodywork of vehicles. In the present invention such a film can be used but, after printing, a contamination control layer is coated onto the film. The ability to stick an image to a surface is retained, but the entirely new function of providing a low-cost and lightweight contamination control sheet that is durable in the short term is generated.

The support layer may comprise a single colour. By this, we mean that the support layer may be the colour of the polymer, or the colour of a pigment or pigments included with the polymer. Alternatively, the colour of the support layer may be a colour printed onto the surface of the support layer.

According to a second aspect, the invention provides a method of providing contamination control using a contamination control sheet according to the first aspect of the invention. If a release liner is present, it is removed to expose the adhesive on the bottom surface of the support layer, and the bottom surface stuck to a surface where contamination control is needed. The release liner may be removed entirely prior to sticking the contamination control sheet to the floor. Alternatively the release liner may be removed gradually, for example, as a roll of contamination control sheeting is unrolled across a floor. To remove the contamination control sheeting, it is detached from the floor and disposed of. If the contamination control sheeting is removed by rolling the sheeting, the adhesive can act to hold the sheeting in the rolled conformation. This provides two distinct advantages. First, the sheeting is held in an easy to handle form. Second, any contaminants held by the contamination control layer are further secured by being sandwiched between the rolls of the sheeting.

In addition to use on a floor as contamination control flooring, the sheet of the first aspect of the invention can also advantageously be used on a door. Doors into medical facilities such as hospitals, doctors' surgeries or into toilets can become a dangerous breeding ground for bacteria and viruses. For example, if an unwell person with microbes on their hands pushes a door push plate, the bacteria or virus can be transferred to the plate. The next person touching it can then pick up the bacteria or virus and may go on to become infected. Currently an antimicrobial spray is often provided by the side of the door but there is usually no protection on the door itself. The antimicrobial spray is obviously only effective if people use it, which many do not.

The present inventors have found that a sheet according to the present invention can advantageously be used to cover a door pull handle or push plate. When the sheet comprises an antimicrobial agent, this will inhibit the growth of bacteria, which may be present, thus reducing the risk of cross contamination. This may enhance current cross contamination reduction procedures. According to a third aspect, the invention provides a method of manufacturing a contamination control sheet according to the first aspect of the invention. Initially a support layer is provided, which is coated on a bottom surface with an adhesive and a release liner. The top surface can then be printed on. The top surface of the support layer is then coated with a transparent or translucent polymeric contamination control layer. The top surface may be coated by means that are already well known. For example, the top surface may be coated with a liquid polymer precursor and the liquid polymer precursor polymerised, or cured, to generate a polymer.

Figure 1 shows a schematic perspective view of a contamination control sheet 10 according to an embodiment of the invention. The sheet 10 comprises a polymer support layer 16 that is coated on a top surface with a polymeric contamination control layer 12. The support layer 16 and polymeric contamination control layer 12 are connected at large surfaces and are flush with one another. A border 17 has been printed onto the top surface of the support layer 16. The printed border 17 runs around, and extends inwards from, the periphery of the top surface of the support layer 16. The polymeric contamination control layer 12 is transparent so that the top surface of the support layer 16, and the border 17, are visible through the polymeric contamination control layer 12. The sheet 10 further comprises a release liner 18 that is shown partly removed from the bottom surface of the support layer 16. The release liner 18 can be removed by pulling the corner of the release liner 18 in the direction of the arrow.

The sheet 10 further comprises a section 13 printed on the top surface of the support layer 16.

In use, the release liner 18 is completely removed and the sheet 10 is stuck to a floor where contamination control is required. The sheet 10 is positioned such that the contamination control layer 12 is above the support layer 16.

Of course, other embodiments and further additions would be apparent to a person skilled in the art. For example, the contamination control sheet may further comprise a section for writing an installation date or keeping a cleaning log. The contamination control sheet may comprise a tapered edging region, or further layers that allow, for example, delayed release of antimicrobial agents.