The edge warping phenomenon of the printed silicone heat transfer label is usually caused by multiple factors such as materials, processes, operations and environment. The following is an analysis of the specific reasons:
1. Material factors: The bonding foundation is not solid
The glue does not match the substrate
Material conflict: If the substrate is a difficult-to-bond fabric such as nylon, Lycra, or a black fabric (the dye contains heavy metals that cause silicone "poisoning"), ordinary glue cannot form an effective bond and is prone to warping.
Glue aging: Long-term storage or use of expired glue will significantly reduce its viscosity, resulting in a weakened bond between the label and the substrate.
Insufficient glue coating: In order to reduce costs and reduce the amount of glue coating, the glue layer is too thin to cover the tiny bumps on the surface of the substrate, reducing the bonding strength.
The label surface material is incompatible with the adhesive
The surface material is too hard: When hard paper (such as thick cardboard) is used on a curved surface or soft bottle body, the rebound force will cause the edge of the label to warp.
Wrong adhesive type: Adhesive is not selected according to the purpose of the label (permanent/removable). For example, removable adhesive is used for long-term pasting scenarios, which is prone to warping due to insufficient viscosity.
Abnormal lamination tension
If the lamination tension is too tight, the label will warp after being peeled off from the backing paper, and it will not be able to fit the surface of the substrate flatly after labeling.
2. Process parameter out of control: Defects in thermal transfer process
Insufficient or uneven temperature distribution
Too low temperature: The hot melt adhesive is not fully dissolved and cannot penetrate the substrate fiber, resulting in weak bonding. For example, the heat press machine displays 150℃, but the actual hot plate temperature is reduced due to the wrapping cloth, and an infrared thermometer is required for multi-point testing.
Temperature fluctuation: Failure of the equipment temperature control system causes the temperature to fluctuate, affecting the consistency of glue curing.
Insufficient or too long time
Too short time: The hot melt adhesive is not completely fused and the bonding strength is insufficient. For example, the cloth pressure must be ≥0.2KG/cm² and maintained for a sufficient time, otherwise it is easy to warp.
Too long: High temperature causes deformation of the substrate or excessive carbonization of the glue, reducing the viscosity.
Uneven or insufficient pressure
Too low pressure: Air remains between the label and the substrate, forming bubbles and causing the edge to curl up. For example, a hard bottle body requires a pressure of ≥0.8KG/cm² to ensure fit.
Uneven pressure distribution: The pressure of the pressure wheel or heat press machine is uneven, and the local area is not firmly bonded.
Wrong tearing time
Hot tearing: The silicone heat transfer lettering film needs to be cold-torn (3-6 minutes after hot stamping). Hot tearing will cause the film to not solidify, and the adhesion is not strong, causing the edge to curl up.
Too fast tearing speed: Rapid tearing may destroy the combination of the glue layer and the substrate, causing the edge to peel off.
3. Omission of operation details: human factors
Incomplete surface cleaning
Dust, oil, plasticizer or paper scraps remaining on the surface of the substrate will hinder the direct contact between the glue and the material and reduce the bonding strength. For example, plastic containers need to be wiped with isopropyl alcohol + compressed air.
Improper labeling process
Uneven manual pressing: No step-by-step pressing or insufficient pressure, resulting in partial non-sticking of the label. For example, a bamboo scraper is required to be scraped flat at 45° in one direction (pressure 0.3-0.5kg/cm², speed 2cm/s).
Positioning deviation: The label is not aligned with the center or edge of the substrate, resulting in one side warping. For example, a positioning hole is required for a bottle with a diameter <5cm.
The hanging test does not meet the standard
After labeling, the adhesion test is not performed (such as the ASTM standard requires a 1kg weight to be hung at 25°C for >120 minutes). If it falls off within 2 hours, it means that the glue oxidation rate is too fast or the adhesion is not strong.
4. Interference from environmental factors: temperature and humidity have a significant impact
Low temperature environment
In winter, the viscosity of the glue decreases, and a special low-temperature resistant glue (such as a special PE material) needs to be used, and it needs to be left to cure in an environment of 15°C+ for 24 hours. If the label is directly applied, it is easy to cause warping due to incomplete activation of the glue.
High humidity environment
In summer, single self-adhesive materials are prone to moisture absorption and curling. You need to use 95-150g plastic-coated thick bottom paper, or unpack and leave for 24 hours to balance the humidity before labeling. Otherwise, the edge of the label will curl up due to moisture absorption and expansion.
Ultraviolet radiation
Long-term exposure to sunlight will decompose the photosensitive components in the glue, resulting in reduced viscosity. For example, labels used outdoors need to use anti-UV glue.
5. Additional risks in special scenarios
Soft bottle body (such as silicone products)
Silicone labels need to reserve 5% shrinkage margin, and the text height should be ≥3mm. If no shrinkage space is reserved, the edge of the label is prone to curling up when it shrinks.
Labeling on large curvature surfaces
When installing on curved surfaces, if the ratio of the surface material to the glue layer is not appropriate (such as 80g coated paper with a 25-30μm glue layer), or if the film material is not selected, the rebound force will cause the label edge to peel off.
Hot-fill container labeling
High-temperature liquids cause the container to deform or the glue to soften. If high-temperature resistant adhesives are not used, the label is prone to warping due to thermal expansion and contraction.