Over recent months there has been huge demand for protective screens for schools. This demand has been caused by the need to prevent person to person transmission of the Covid 19 virus.
This post is intended to provide information about the options for clear transparent protective screens for schools to those who have little experience in plastics. In this post we will discuss some of the more basic information. In an upcoming post we will discuss some of the flammability issues and regulations.
Types of clear plastic.
There are a number of types of clear plastic. These include polystyrene, acrylic, PET-G and polycarbonate.
Polystyrene
The most brittle of these is the polystyrene. Polystyrene is used to make the old CD jewel cases. These are very delicate and can be easily broken. Although polystyrene sheets are cheap, they would quickly become broken. Even worse in a school environment, any breakages would lead to sharp edges. These edges would be a safety hazard. Despite the cost advantage, we would not recommend using polystyrene sheets for protective screens.
Acrylic (Plexiglas)
Acrylic is known by the trade name Plexiglas. It is a very optically clear material, but it is also prone to breaking., although it is better than polystyrene. For applications where the protective screen can be fixed or secured, Acrylic is a valid option. Where the screen is not secured and could be knocked over, we would not recommend it. To counter the breakage issue, you can use a thicker piece of acrylic, but this does add significantly to the weight. We will discuss thickness and weight later.
Acrylic does have an advantage of being one of the most scratch resistant of the clear plastics. However, it is still not totally immune to scratches and a key or pencil could easily scratch the material.
PET-G
PET-G is much more resistant to breakage than Acrylic. It also has the advantage of being about the same price. PET-G is often used for face-shields and would be a good choice for protective screens.
Polycarbonate
Polycarbonate is virtually unbreakable. You cannot break polycarbonate from a reputable supplier even with a hammer. The downside of polycarbonate is that it is about 25% more expensive than acrylic and PET-G.
Polycarbonate is also prone to surface scratches. This can be improved by adding a hard coat to the surface, but this can double the cost of the sheet.
Thickness and Weight
The weight of the sheet is an important factor in the school environment. You would not want a heavy sheet to fall on a small child. To give you an idea of the weight we have the following approximate calculation for all of the above materials. For each 1/8″ thick of material the sheet will weigh 0.75 lbs per square foot.
Using this calculation if we assume we are using 3/8″ thick material and installing a 3′ high and 6′ long protective screen, the weight of the sheet would be 3 x 18 sqft x 0.75 lbs/sqft = 40.5 lbs. You would obviously not want a 40lb sheet falling on a small child.
It is therefore important to keep the weight down or make sure that the sheet is permanently secured to prevent falling. The most obvious step to weight reduction is to keep the width and length to the minimum required. Keeping these dimensions low is also important in regard to the thickness. If you use a large size sheet, the sheet can be very flexible and not rigid. This can cause its own set of problems. If the screen is small, say less than 2′ x 2′ it may be possible to use an 1/8″ thick sheet. As you get larger, you may need to increase to 1/4″, 3/8″ or thicker to maintain rigidity. For example in hockey rinks we routinely use 1/2″ thick sheets for 6′ x 8′ sheets.
You can see that keeping the size and thickness down is important to keeping the weight of the sheet down. A 1/8″ x 2′ x 2′ sheet would weigh about 3 lbs which is a much more manageable weight than the 40 lbs sheet that we discussed earlier.
Cutting the sheet
It is possible to cut plastic sheet yourself, but for protective screens we would strongly recommend that you do not. There are a number of hazards to consider. The edges of a poorly cut sheet could be very sharp. Also the corners need to be professionally rounded. Also any fixing holes need to be professionally drilled to prevent sharp points.
We would recommend that a plastic distributor or fabricator cuts the screens for you. In the purchase order that you place with them we recommend that you use the following language:
- All cut or routed edges are to be smooth to the touch.
- All edges are to be broken to eliminate sharp points.
- All corners are to be rounded
- All holes drilled or routed are to be smooth to the touch.
We see many cases of poorly manufactured screens that could be a safety hazard due to sharp edges.
Where to buy protective screens.
If you only need a few protective screens for schools (say less than 20), we would recommend that you just buy them off the internet and buy a standard design. The cost per protective screen may be reasonably high, but it is not going to be any cheaper trying to get someone to design a custom screen. We would strongly recommend that you do not try and fabricate your own screen as the potential for causing hazards is high. You are also unlikely to achieve any significant cost saving.
If you need several hundred screens, and particularly if you need custom designs, we would recommend that you contact a national Plastics distributor such as Laird Plastics, Curbell Plastics or Polymershapes. They have plastic materials and fabrication equipment on site and will be able to assist in any design.
If you need several thousand screen for a large school district, please feel free to contact us at HighLine and we will be able to advise you on how to manage your project.