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I'm sure everyone has at least heard of these concepts! But what exactly are the true meanings of these concepts, you may not know! Today, let's come together with the editor to take a look at these meanings.
Tensile strength
Tensile strength is a measure of the ability of paper to resist external tension. It refers to the maximum tensile force that a certain width of paper or paperboard sample can withstand, with the unit being kN/m. The former unit was kgf/15mm (1kgf/15mm = 0.6538kN/m).
Breaking length can eliminate the influence of different weights and is convenient for comparison with tensile strength.
Breaking length refers to the length required for a certain width paper strip to break under the gravitational force of its own weight.
The tensile strength of the cross-section of paper refers to the tensile force per unit area on the cross-section of the sample, with the unit being KPa. The former unit was kgf/cm2 (1kgf/cm2 = 98KPa).
Elongation is an indicator measuring the toughness of paper and paperboard. It refers to the percentage increase in length of the sample when it is stretched to break compared to its original length.
Compressive strength
Compressive strength refers to the maximum pressure that a material can withstand until it collapses under compression.
Since most packaging boxes are often stacked multiple layers during transportation and storage, packaging boxes need to have certain compressive strength to ensure that the contents are not damaged.
The compressive strength of paper boxes mainly depends on the compressive performance of the constituent materials, so the compressive strength of the paper box can be indirectly evaluated by testing the compressive strength of the paperboard used to make the paper box.
The compressive strength of paperboard is expressed in terms of the compressive ability per unit length and per unit area.
The main indicators characterizing the compressive strength of paperboard are ring compressive strength, flat compressive strength and edge compressive strength.
Breaking strength
Breaking strength refers to the maximum uniform pressure that a paperboard can withstand per unit area, expressed in Pa. The former unit was kgf/cm2 (1kgf/cm2 = 98KPa).
Breaking strength is an important property of paper bags, packaging paper and paperboard. It is affected by the bonding force between fibers and the average length of fibers. It is a composite function of tensile strength and elongation. Most of the stress is a tension formed by the pressure difference across the paper sheet when it breaks.
Since the deformations in all directions are basically equal, an equilibrium stress is generated in the paper.
Due to the small longitudinal elongation of the paper, it becomes a longitudinal tension after being compressed, so the cracks of the sample are generally perpendicular to the longitudinal direction of the paper.
Penetration strength
Penetration strength of paperboard refers to the work required to pass a certain-shaped cone through the paperboard, including the work required to start the penetration and to tear and bend the paperboard into a hole. It is expressed by the total energy loss of the cone, with the unit being kgf.cm (1kgf.cm = 0.098J), and the international unit is J.
Penetration strength belongs to dynamic strength, simulating the strength performance of paperboard when it is suddenly subjected to an impact force.
For example, in the loading and unloading, transportation and other processes of paper packaging boxes, they are often damaged due to the impact of sharp and hard objects.
The essential difference between penetration strength and breaking strength is that breaking strength is uniformly applying pressure to burst the sample, which belongs to static strength; while penetration strength is suddenly applying an impact force to puncture the paperboard, which belongs to dynamic strength.
Therefore, for paperboard packaging materials, penetration strength is more practically significant.
Tensile strength
Tensile strength is a measure of the strength performance of paper and paperboard in resisting bending, also indicating its softness or stiffness. Tensile strength is closely related to the thickness of paper and paperboard.
Theoretically, tensile strength is proportional to the cube of thickness. For example, when the tightness remains constant, the increase in tensile strength is proportional to the cube of thickness; when the weight remains constant, the increase in tensile strength is proportional to the square of thickness; when the thickness is constant, tensile strength is proportional to the tightness.
Paper with high pulp consistency has greater tensile strength.
Therefore, paper and cardboard with a certain amount of straw pulp added have better stiffness.
The rigidity of cartons reflects the ability of the cartons to resist deformation, and it mainly depends on the stiffness of the cardboard.
If the cartons are subjected to compressive loads or filled with items and have insufficient bending resistance, they are likely to deform or even rupture.
Tear resistance
Tear resistance of paper and cardboard refers to the number of times the tested sample undergoes a certain angle of repeated folding under a certain tension.
The longitudinal tear resistance is obtained by testing the longitudinal sample, and the transverse tear resistance is obtained by testing the transverse sample.
Generally, the longitudinal tear resistance is higher than the transverse tear resistance, which is due to the arrangement of fibers and the strong bonding force of longitudinal fibers.
However, there are abnormal phenomena, which involve the flexibility and fluidity of paper and cardboard.
Tear resistance is a disguised tensile strength test, and its result is greatly affected by the flexibility of the paper.
Tear strength
Tear strength of paper and cardboard refers to the force required to continue tearing the cut sample for a certain distance, also known as internal tear strength, expressed in mN. The former unit was gf (1gf = 9.807mN).
Edge tear strength is the force required to tear along one side of the sample with a pre-set cut, along the same plane, for a certain length, expressed in N.
The work done in tearing paper and cardboard includes two parts, namely the work done in pulling the fibers apart and the work done in breaking the fibers.
Fiber length is an important factor affecting the tear resistance of paper and cardboard.
An increase in fiber length leads to an increase in tear resistance, because an increase in fiber length means an increase in the work done in pulling the fibers apart.
Internal tear strength is one of the important testing items for bag paper, packaging paper, and packaging cardboard.
For banknote paper and candy packaging paper, edge tear strength has specific significance.
Corrugated cardboard bonding strength
Bonding strength describes the bonding performance between the crests of corrugated cardboard and the surface paper (or core paper) of the unit. The unit is N/m.
The principle of testing corrugated cardboard bonding strength is to insert a needle-shaped accessory between the crests of the corrugated cardboard sample and the surface paper (or core paper), and then apply pressure to the needle-shaped accessory inserted into the sample to make it move relative to each other until the separated parts are separated.
