There are two basic types of paper plate designs made on modern thermoforming paper plate machines: smooth scored and fluted. Generally, the fluted plate is recognized as an older design for inexpensive, picnic plates while the smooth scored paper plate is a more recent development used for partyware and high graphics.
A. Smooth Scored
Generally, the blank size of a smooth scored paper plate will be between 105.0% and 107.3% of the finished size. Factors affecting this are the sidewall angle, depth and curved portions of the design. Two point scoring rule is used to provide the scoring of the blank which is generally placed at increments of 9º – 15º depending upon the depth and sidewall angle. The deeper the paper plate and the steeper the sidewall angle, the more scores that are required to take up the excess paperboard as the diameter of the blank is being reduced, and the slower the thermoforming paper plate machine will run.
One of the most important factors affecting the rigidity of the paper plate is the design of the contour. Most high quality, smooth scored paper plates use a sidewall angle of 25º-35º as measured from vertical. Generally, the steeper the sidewall angle the more rigid the paper plate although the plate becomes increasingly more difficult to form. Also, the steeper the sidewall angle, the more blank diameter reduction that occurs making a smaller finished plate for the given blank.
The deeper a paper plate is formed, the more paperboard that must be gathered into the wrinkles or pleats providing a double layer of paperboard in those areas. Therefore, if those pleats are well pressed, the plate will be more rigid than its shallower counterpart. Most smooth scored paper plates have a depth to finished outside diameter ratio of .070 – .078. Of course the deeper the plate, the smaller the OD will become from a given blank.
Indenting or forming a raised bottom in the container will provide additional stiffness to the paper plate. In addition, this “trough” formed around the perimeter of the bottom between the indention and the first curved portion will provide a recess for excess liquid from foods put onto the paper plate during normal use. This indention will also prevent the paper plate from spinning and will ensure that it sits flat on the table. Indentions are usually formed to be .09 – .15 as deep as the overall depth for paper plates. In other words, if the plate depth is .75 inches, then the raised portion should be between .0675 inches and .1125 inches (or approximately 1/16” and 1/8”).
The first curved portion of the paper plate (connecting the sidewall to the bottom) should have a radius of .055 – .065 of the OD of the plate. The smaller this radius, the stiffer the plate. However, a smaller radius is more difficult to form and will require more paperboard than a larger one.
The second curved portion of the plate (connecting the sidewall to the rim) should have a radius of .020 – .035 of the OD of the plate. As is the case above, the smaller this radius, the more rigidity to the design. Once again, the smaller the radius, the more difficult it is to form the plate on the paper plate machine and the more paperboard that will be required.
Within reason, the wider the rim on the paper plate, the more rigid the plate will be. The rim when taken into account structurally with the sidewall and bottom panel form a partial “I” beam shape. Overforming of the rim, or turning it downward on the die by 10 to 15 degrees will also result in increased strength.
Finally, the outside lip of the paper plate can play an important role in the design. For rigidity purposes it is best to turn this down to a 45° – 55° angle from vertical. However, this makes the plate difficult to form and also can cause uneven appearing stacks of plates due to the critical nature of locating the blank in the exact position each stroke of the machine. Compromises such as a radius on this outside lip can add some strength without causing much difficulty in the forming process. Other possibilities include the use of more complicated die designs to compensate for the issues surrounding the turned down lip. However, the more complicated the design, the slower the paper plate machine must be run to achieve high quality paper plates.
B. Fluted Plates
Fluted plates are the type of paper plates that generally do not use scores and pleats or wrinkles to take up the excess paper in the paper plate thermoforming process, but rather, use a series of “hills and dales” or indentions. Because it is not possible to take up as much paper using this system as it is with scores and pleats, it is therefore not advisable to make deep or steep sidewall angled plates as they require more diameter reduction. If deep or steep sidewall angled plates are attempted using only flutes, the result will be a paper plate with many uncontrolled wrinkles.
Because fluted paper plates are generally made shallower and with less steep sidewall angles, it is therefore possible to use less paperboard in making the standard finished sizes of 6”, 7”, 8”, 9” and 10”. By far the most popular sizes of fluted plates are the 6” and the 9”.
In addition, because fluted plates are shallower and less steep, it is possible to form several plates in the same stroke of the die by inserting two, three or four blanks of paperboard into the die simultaneously. This is known in the industry as “multi webbing” and is accomplished by simply running multiple webs of paperboard thorough the paper plate machine at the same time. If multiple webs are being utilized, it is important that the dies have been machined with the proper clearances. Otherwise, it is likely that the paperboard will fracture and tear as it is being formed.
In designing a fluted paper plate, it is important that the number and size of flutes are correctly designed to the amount of paperboard made available by the diameter reduction. If the flutes are too few or too small in terms of surface area, excess wrinkles will occur. If the flutes are too large or too many, the paperboard will fracture and tear in the fluted areas.
When the correct number and size of flutes are designed into the plate, and they are pressed properly in the thermoforming process, they also serve as areas of strengthening ribs. In a few instances, flutes are combined with scores in order to provide rigidity rather than areas for paperboard take up.