The fold design of a blister heat seal packaging color card must balance forming function and heat sealing performance. The key is to minimize physical damage and stress concentration in the heat seal layer at the fold area through structural optimization. The interaction between material deformation behavior at the fold and the heat sealing process determines the final packaging's seal integrity and structural stability. This requires a systematic design approach based on three dimensions: material properties, fold shape, and processing sequence.
Material selection is the foundation of fold design. The substrate of a blister heat seal packaging color card must meet both folding toughness and heat sealing compatibility. Excessively soft paper is prone to cracking during folding, while overly hard board material will have difficulty forming a neat fold. High-density kraft paper or composite paper is typically used. Its fiber structure allows for stress dissipation through fiber slippage during folding, reducing the risk of surface fracture. To enhance heat sealing performance, a hot melt adhesive layer or a co-extruded heat sealing resin can be applied to the blister heat seal packaging color card surface. However, the adhesion between the coating and the substrate must be ensured to prevent detachment after folding to avoid seal failure due to coating delamination during heat sealing.
The geometry of a crease directly influences stress distribution. Sharp creases can easily create stress concentration points at the corners, leading to uneven material stretching during heat sealing. However, rounded creases distribute stress through a smooth transition, reducing local deformation. The crease radius should be determined based on the packaging structure. A radius of at least twice the material thickness is generally recommended to balance forming ease and heat sealing reliability. Furthermore, the crease depth must be precisely controlled. Too deep will cause a sudden drop in material thickness, leading to uneven heat transfer during heat sealing, while too shallow will prevent a clean fold. A crease depth of 60%-80% of the material thickness is generally appropriate.
Matching the crease direction with the fiber orientation is crucial. Paper fibers are anisotropic. Folding along the fiber direction promotes plastic deformation and resists breakage. Folding perpendicular to the fiber direction is more likely to cause fiber breakage and surface fuzzing. When designing, creases should preferably be parallel to the longitudinal fiber direction. If structural constraints necessitate a transverse fold, pre-indentation should be used to disrupt the transverse fiber connections and reduce folding resistance. For multi-layer composite blister heat seal packaging color cards, the fiber orientation consistency of each layer must also be considered to avoid warping after heat sealing due to interlayer stress differences.
Optimizing the processing sequence can reduce secondary damage. If the blister heat seal packaging color card is printed before folding and heat sealing, the flexibility of the printing ink must be compatible with the folding deformation. Otherwise, the ink layer may crack during folding, exposing the substrate and causing poor heat sealing. Using water-based or UV inks can improve flexibility. In addition, avoid using inks containing mineral powder to prevent powder from falling off during folding and affecting the heat seal interface. If localized hot stamping or lamination is required at the crease, ensure these processes are completed before folding, and ensure that the elongation difference between the additional layer and the substrate is less than 15%. Otherwise, separation between the layers may occur during heat sealing.
Heat sealing process parameters must be coordinated with the crease design. Uneven thickness due to material deformation in the crease area requires segmented temperature control or pressure compensation during heat sealing. For example, appropriately reducing the heat sealing temperature or increasing the pressure duration at the crease can compensate for heat loss caused by material thinning and ensure sufficient melting of the sealing layer. Furthermore, the shape of the heat-sealing mold must match the crease structure to prevent the mold edge from causing secondary compression of the crease during heat sealing, potentially leading to material cracking.
Verification of the crease design requires a combination of simulation testing and actual spot checks. During the prototype stage, folding and unfolding cycle testing can be used to observe whether white marks or cracks appear at the crease. White marks indicate irreversible plastic deformation in the material, potentially affecting heat-seal strength. In actual production, the heat-sealed packaging must be tested for leak tightness, focusing on the intersection of the crease and the heat-seal line. Negative pressure testing or dye penetration testing can be used to verify leak tightness and ensure that the crease design does not compromise the overall protective function of the packaging.
The crease design of the blister heat-seal packaging color card requires systematic control across a range of steps, including material adaptation, geometric optimization, directional control, sequence adjustment, parameter coordination, and validation testing. This ensures both folding functionality and heat-sealing performance, ultimately meeting product packaging requirements for leak tightness, structural strength, and appearance quality.
