Heat-seal film manufacturer: Heat-shrink films are primarily used for labeling, heat-shrink outer packaging, or as packaging films. The polymers commonly employed to produce heat-shrink films include PVC, PE, PS, and PET. After heating, the film is stretched, cooled, and set—typically without undergoing additional thermal setting—to yield a heat-shrink film. Near the polymer’s glass transition temperature (Tg), the molded polymer is subjected to biaxial stretching followed by heat treatment, which locks the polymer chains into a contracted state and forms the heat-shrink film. From raw material to finished heat-shrink film, the process involves a decrease in entropy, resulting in an inherently thermally unstable state. Once the heat-shrink film undergoes tempering, its molecular chains rapidly revert to a disordered, coiled configuration, causing the film to contract. This characteristic makes heat-shrink films particularly suitable for producing labels on irregularly shaped bottles. Heat-seal film manufacturer: From a functional standpoint, heat-shrink sleeve labels offer waterproofing, corrosion resistance, impact resistance, tear resistance, and odorlessness; they can also serve as anti-counterfeiting markers and protect consumers from accidents caused by damaged or broken containers. Such labels are recyclable, providing significant environmental and cost‑saving benefits. However, designing heat-shrink sleeve labels presents numerous challenges. Heat-seal film manufacturer: Polyethylene heat-shrink film is a widely used substrate in the market for manufacturing heat-shrink waterproof sleeve labels. This type of film boasts moisture resistance, fire safety, high transparency, high gloss, and excellent shrinkage. Nevertheless, when burned, the material readily releases harmful gases, posing environmental concerns. Heat-seal film manufacturer: As a new material, heat-shrink film is an environmentally friendly, skin‑contact packaging solution. It features high strength, superior rigidity, excellent gloss, high shrinkage rates, and compliance with food‑safety standards.

Sealing is a common method used in stretch‑wrap film. Seal‑to‑seal compressive strength is one of the criteria for certifying product quality. Aside from ambient temperature, sealing pressure also follows certain patterns. During production, it is important to maintain an appropriately balanced pressure.

This method yields better sealing performance, but during production, the pressure can sometimes remain unstable. What causes uneven sealing pressure in stretch‑wrap film? 1. Deformation of the heat‑seal blade: Heat‑seal blades are typically made from aluminum or copper, materials that offer excellent thermal conductivity at a reasonable cost. Both of these materials are relatively soft; therefore, if the fastening screws are tightened improperly during use, the heat‑seal blade may not bear the intended load.

Moreover, even after frequently replacing the dedicated tooling, the heat‑sealing blade can still become deformed. Therefore, when using a heat‑sealing blade, it is essential to follow the appropriate installation procedure. 2. Low dimensional accuracy of the heat‑sealing blade Poor machining accuracy of the heat‑sealing blade can result in an uneven surface, leading to non‑uniform sealing pressure during the sealing process and compromising the compressive strength of stretch‑wrap packaging. 3. Contamination or damage to the heat‑sealing blade surface Surface contaminants, irregularities, or scratches on the heat‑sealing blade can also cause uneven sealing pressure. In addition, if molten epoxy resin adheres to the blade surface and is not promptly removed, it will adversely affect the sealing strength.

Therefore, during knife alignment, the epoxy resin inside the heat-sealing blade must be thoroughly cleaned. 4. Strength and Elasticity of Silicone Rubber The quality of silicone rubber is a critical factor in ensuring uniform sealing pressure. Consequently, the silicone rubber must possess adequate strength and elasticity.

After prolonged operation, if the silicone rubber deteriorates—losing its elasticity due to aging—the sealing pressure may no longer be adequately maintained. Scratches on the silicone rubber surface can lead to bubble formation after sealing, which will severely compromise the seal strength.

When selecting silicone rubber, be sure to pay attention to its strength and elasticity. The typical strength requirements for silicone rubber are as follows: for sealing aluminum‑foil pouches, a strength of HS70 is specified; for sealing general materials, a strength of HS50–HS60 is required.