Most people at the first sight of PK Sleeve will normally say "What a good idea !" . But they have never realized that inside the appearance it has taken years of research.
The mechanics of PK Sleeve involves the study of strength of a narrow corrugated cardboard strap subjected to the combined stresses of tensile and shear. Until the invention of PK Sleeve, the corrugated cardboard has never been applied as a tension material since there are so many cheaper and stronger materials available. But since the PK sleeve is totally made of corrugated cardboard, to satisfy a liftable yet reliable function, a careful study is inevitable.
The first PK Sleeve prototype, cut by hand, could not withstand 100 grams. Now, it can handle at least 2,700 grams and allow more than 500 times back and forth swinging while carrying 16 oz of coffee. So, It is not just a "good idea", it is a "technology"
A Perfect Coupling of Aesthetics and Mechanics by Nature
There are at least 7 key technologies behind the looks. Ignoring any of them may result in the sleeve unusable, damaged, costly, or inconvenient to use.
Corrugated cardboard used for cup sleeve is commonly consisting of a face liner( for printing), a base liner and a flute layer. It is a composite material and presenting ani
sotropic property in the aspect of strengths. It means that the tension and anti-tearing strengths are significantly different in machine direction and cross direction. In order to achieve the best performance of the straps, we have used three dimensional numerical method to analyze the stress distribution and developed a strap with gradient arc shape. This particular shape would warrant the straps with the longest length and strongest strength. The bonus is when two straps buckled, it forms a beautiful handle. We have no intention to design the strap by this shape, it is called by nature. So we always said PK Sleeve is A Perfect Coupling of Aesthetics and Mechanics by Nature
Single-loop versus Double-loop Handle Structure
A liftable facility such as a plastic bag with two ears (loops). When we hold together these two ears it becomes a strong handle. If we tear off one of the fixed ends of each ear and tie the two straps together it will form a much longer single-looped handle than the oringinal (Double-loop). Therefore, the single-loop structure will generate almost twice the length than that of double-loop for the same sleeve size. This is important since for the regular size of cup sleeves, the double-loop structure can never provide sufficient space for lifting.
Single-loop is weaker than Double-loop ?
To most of the applications, single-loop structures are weaker than the double-loop. But It is not true in this application. Due to the configuration of the double-loop structure, the fixed-ends of the straps are comparatively rigid that would subjected to excessive moment stress when the cup is shaked or swinged laterally. This moment stress will turn into a tearing force along the cross direction of the corrugated cardboard and damage the fixed-ends of the straps. The single-loop structure, in our design, at the end of the strap is similar to a hinged-end device thus minimize the moment stress. The hinged-end device is implemented by cutting an inclined angle at the end of the strap. Unfortunately, the double-loop can not do the same due to the limitation by its configuration.
PK Sleeve Allow Carring Two to Three Cups with One Hand
Single-loop structure inherents a very flexible handle. The handle can be easily moved in all directions. Therefore we can carry 2 to 3 cups of coffee with one hand easily. 