Application of the coldest stamping forming hard s

The application of cold stamping forming hard pieces

the rapid expansion of the capacity of battery diaphragm by aluminum plastic blister packaging of drugs is also known as blister packaging; PTP packaging for short. The packaging material diaphragm is formed by heating, vacuum forming or cold stamping to form grooves suitable for tablets, capsules and other shapes, and then filled with drugs. Then heat seal the drug packaging with aluminum foil coated with heat sealing coating to form unit packaging

the covering material of aluminum-plastic blister packaging of drugs is generally aluminum foil (called aluminum foil for drug blister packaging), and the foam forming substrate is generally polyvinyl chloride (PVC) hard sheet. However, with the continuous development of the pharmaceutical industry, the traditional packaging method has exposed its shortcomings. Due to the limited barrier performance of PVC hard sheets, it is difficult to ensure that the quality of drugs will not change during their service life. In view of the limited barrier performance of ordinary blister packaging, people developed cold stamping and pressing hard films in the early 1980s with a new concept. Cold stamping molding uses stamping molding instead of vacuum Blister molding of the original ordinary blister packaging, so that the blister packaging sheet can use pure aluminum foil composite as the foaming material. The application of high-strength alloy aluminum foil in cold stamping hard films also makes cold stamping hard films have extremely high water vapor, oxygen and light insulation properties that can not be achieved by any other materials

Figure 1: the cold stamping hard film of aluminum plastic blister packaging of drugs is generally composed of three functional layers: surface support strength layer, intermediate aluminum foil barrier layer and inner surface heat sealing layer. The surface support layer can be printed with the color or pattern required by the customer, and the layers are bonded together to form a composite film as a whole. The surface support strength layer of the cold stamping formed hard sheet requires smoothness, good transparency, high mechanical strength, excellent impact resistance, and certain wear resistance and puncture resistance, which plays a mechanical protection role for the whole package. The surface support layer of cold stamping hard sheet generally adopts biaxial tensile nylon film (BOPA) with high strength and excellent impact resistance. Due to the great impact and tension of the cold stamping formed hard sheet in the cold stamping bubble forming process of the package, 15 μ M-thick BOPA can not meet its requirements. Except for shallow stamping, 25 is generally used μ M thick BOPA is used as the surface support strength layer. For shallow stamping occasions, in order to save costs, biaxially stretched polyester film (BOPET) or biaxially stretched polypropylene film (BOPP) can also be used to replace biaxially stretched nylon film

in addition to the barrier function, the intermediate aluminum foil barrier layer used for cold stamping forming also has the functions of strength support, stamping tensile resistance and so on. Therefore, different from the intermediate aluminum foil barrier layer used for cold stamping forming of general soft packaging, in addition to the barrier function, it also has the functions of strength support, impact resistance, compression tensile as an important part of the instrument, such as the fixture of electronic tensile testing machine, Therefore, it is different from general aluminum foil for flexible packaging. The aluminum foil used in cold stamping is not ordinary pure aluminum foil, but alloy aluminum foil with high strength and good extensibility. Because of the cold stamping, the hard pieces need to be stamped. Therefore, the thickness of aluminum foil used is much thicker than that of ordinary composite film, generally 45 μ For m-thick aluminum foil, the thickness of aluminum foil can be appropriately reduced for the occasion of stamping into shallow bubbles, and generally the minimum can be reduced to 3 μ M thick. For occasions where the stamping bubble is particularly deep (≥ 15mm), or where the cold stamping forming hard sheet is required to have good stiffness, the thickness of aluminum foil can be appropriately increased, and the maximum thickness can be increased to 70 μ m。

the heat sealing layer on the inner surface of the cold stamping forming hard sheet is generally PVC hard sheet, so the cold stamping forming hard sheet can be heat sealed with PTP aluminum foil for drug packaging like PVC hard sheet for ordinary blister packaging. The PVC used for cold stamping hard sheet is different from ordinary PVC. Considering the factors such as compounding and stamping, ordinary plasticizers and lubricants are usually not used, but the internal plasticization and internal lubrication are carried out by grafting plasticizer factors into the PVC molecular chain segment. At the same time, in order to improve the impact resistance of PVC, more reinforcing agents are added to PVC hard sheets than ordinary PVC hard sheets, so that it has good composite properties and stamping forming properties. The thickness of PVC in cold stamping hard sheet is generally 60 μ m. When the product is required to have high rigidity and stiffness, the thickness of PVC can be increased appropriately, up to 100 μ M thick, polypropylene and polyethylene can also be used in some special occasions; Polyester and Surlyn resin are used as heat sealing layers

Figure 2: PVC hard sheet for cold stamping. The surface support strength layer, aluminum foil barrier layer and inner surface heat sealing layer in the cold stamping forming hard sheet are bonded by adhesive, which organically combines them into a composite material. In order to ensure that the hard sheet formed by cold stamping will not separate and fracture under the strong impact molding force, the selection and use of its adhesive is very critical. Generally, the bonding strength of aluminum foil with surface support strength layer and heat sealing layer after bonding is required to reach more than 8n/15mm. The ratio of soft segment and hard segment of molecular chain segment in polyurethane adhesive should also be controlled in the process of formula design; To meet the requirements of cold stamping. Ordinary adhesives are difficult to meet the above requirements, so the adhesives used for cold stamping hard films are generally specially prepared special adhesives

although the cold stamping blister packaging has good appearance and extremely high barrier performance, the product has many characteristics different from other packaging materials in the use process, and the following problems often occur in the use process:

1. Cracks and pinholes of aluminum foil occur on the blistered blisters of the cold stamping hard sheet during foaming; As well as the separation between composite membranes, the reasons for these defects mainly include the following three categories:

the first category is the quality problems of cold stamping hard films. Cold stamping hard sheet is a product with high technical content, which has many special requirements for raw materials and production technology. If all links in production are not well controlled, it is very easy to have quality problems. The quality problem of cold stamping formed hard films can be easily determined by replacing cold stamping formed hard films of different batch numbers or even different manufacturers

the supporting strength layer of the cold stamping forming hard sheet is mainly 25% of the biaxially stretched layer on the outer surface μ M thick nylon film. The hardness of nylon film is low; It is easy to be scratched by hard objects; Once the nylon surface is scratched, even a slight scar; Will greatly reduce the strength of the nylon film, resulting in the fracture of the aluminum foil and nylon film at the scratched part of the cold stamping hard piece during the stamping bubble forming process. In the actual production process, the scratch, especially the slight scratch, of the cold stamping forming hard sheet is difficult to be found with the naked eye, and it is often found when stamping bubbles; Thus causing losses. The scratch of cold stamping formed hard film is generally caused by the inflexible rotation of the guide roller during the operation of the composite film, the foreign matters on the guide roller, and the contact of the composite film with the fixed part of the equipment (such as electrostatic brush). The scratched and huge market demand may be generated not only in the production process of the manufacturer, but also in the packaging equipment of the user

Figure 3: Biaxially Stretched Nylon film on the outer surface of cold stamping formed hard film

cold stamping formed hard film contains hygroscopic nylon material. After nylon absorbs moisture, it is easy to cause the separation of nylon film and aluminum foil during the stamping process of cold stamping formed hard film, and lead to the rupture of tin foil or pinholes, thus reducing the foaming rate of cold stamping formed hard film. Even for the finished products of cold stamping blister packaging, the foam forming part is easy to separate the nylon and aluminum foil after being parked in a wet environment (it does not separate the layer when it is first produced, but it separates the layer after being parked in a wet environment for a period of time), so the cold stamping hard sheet and its double aluminum blister packaging products. Store in a dry environment

the second kind is that the stamping die design is defective. The cold stamping forming hard sheet uses mechanical stamping to generate a blister. During the stamping process, the force and tensile deformation of the cold stamping forming hard sheet are very large, which is almost close to the limit of the material. If the stamping die is not designed properly, it may lead to the cracking of aluminum foil in stamping forming. The design of the die includes the material of the die and the geometry of the punch

generally speaking, polyoxymethylene molds have lower friction coefficient and better stamping performance than stainless steel molds, and polytetrafluoroethylene molds have lower friction coefficient and better stamping performance than polyoxymethylene molds. A low friction coefficient is conducive to reducing the friction in the stamping process, avoiding the uneven stress of the cold stamping materials, and greatly avoiding the aluminum foil cracks and the separation of the composite film in the stamping process. For drugs of the same size, reducing the friction coefficient can have a larger stamping drawing ratio, so as to effectively reduce the area of packaging materials and reduce costs. The friction coefficients between PTFE, POM and stainless steel molds and the PVC surface of cold pressed hard sheets are 0.4, 1.2 and 2.1 respectively. For drugs with the same packaging and the same depth, the required foaming area ratio is 1:1.2:1.4. The use of polytetrafluoroethylene punches can effectively prevent the cracking of aluminum foil and the separation of composite film in the stamping process, and at the same time, it can save packaging materials. Therefore, except for shallow stamping occasions, polytetrafluoroethylene is generally used as the stamping die. Of course, polytetrafluoroethylene also has a disadvantage, that is, the hardness is not high enough, and the stamping die is easy to be damaged and scratched. Using the damaged die head to punch bubbles, it is easy to cause aluminum foil pinhole cracking and increase the scrap rate

in addition to the material of the die formed by cold stamping, the size and geometry of the punch have a great impact on the cracking of aluminum foil and the separation of composite film. There are generally two types of stamping die heads: smooth transition type and stepped transition type. The blister punched out by the smooth transition die is beautiful, but relatively speaking, its performance of stamping depth resistance and stamping fracture resistance is poor. The stepped transition die head is divided into several angular steps, which are stretched in stages during the stamping process. The cold stamping formed hard piece has less contact area with the stamping die head during the stamping process, which is conducive to uniform stretching and foaming. Because the size of the stamping die is very easy to cause traffic accidents and the shape has a great impact on the foaming rate of stamping forming, people have specially developed the corresponding computer software, which can automatically design the best shape of the stamping die according to the overall size of the packaged tablets. So as to avoid the local stress and tension of the cold stamping hard sheet in the stamping bubble forming

the third type is improper stamping process control. The hard sheet formed by cold stamping is extruded into bubbles by mechanical stamping. As a metal layer material, the elongation of aluminum foil in cold state is limited, although the aluminum foil used for cold stamping is special