A plastic processing technology. The main principle is to heat and soften a flat hard plastic sheet, then vacuum it to the surface of the mold, and then cool it into shape. Vacuum Forming, often called blister, is a plastic processing technology. The main principle is to heat a flat hard plastic sheet to soften it, then use vacuum adsorption on the surface of the mold, and then cool it to form. It is widely used in plastic packaging, lighting, advertising, decoration and other industries.
Principle
Vacuum forming is to fix the thermoplastic plastic plate or sheet on the mold, use a radiant heater to heat it to reach the softening temperature, and then use a vacuum pump to remove the air between the mold and the plate (sheet) to make the plate (sheet) The parison is formed according to the contour of the mold. As the degree of vacuum increases, the forming pressure below the parison is only 0.06-0.085MPa, while the air pressure above the parison remains at about 0.1 MPa. After cooling and shaping, compressed air is used to blow the product out of the mold and demould.
The materials processed by vacuum forming are thin sheets of polyvinyl chloride, polystyrene, polyethylene, etc.
Usage classification
Blister packaging: a general term for using blister technology to produce plastic products and using corresponding equipment to package the products.
Blister packaging products include: blister, tray, blister box, synonyms include: vacuum cover, blister, etc.
Main advantages
The main advantages of blister packaging are that it saves raw and auxiliary materials, is light in weight, easy to transport, has good sealing performance, and meets the requirements of environmentally friendly green packaging; it can package any special-shaped products, and no additional buffering materials are needed for packaging; the packaged products are transparent and visible. The appearance is beautiful, easy to sell, and suitable for mechanization and automatic packaging, which facilitates modern management, saves manpower and improves efficiency.
Production equipment
Blister packaging equipment mainly includes: blister forming machines, punching machines, sealing machines, high-frequency machines, and folding machines.
The packaging products formed by encapsulation can be divided into: plug-in cards, suction cards, double-blistered shells, half-blistered shells, half-folded blisters, three-folded blisters, etc.
Tri-fold blister packaging
Three-fold blister packaging is to fold the blister into three sides (front, bottom, and back) to form an extra bottom edge so that the product can stand on a flat surface. Its characteristic is that instead of using high-frequency edge sealing technology, buckles are made at certain positions of the bulb to connect the bulb. If necessary, staples can be added. In terms of material selection, PET hard sheets can be used to achieve environmentally friendly materials. purpose, suitable for large-diameter product packaging.
Issues that should be noted: 1. Since there is no high-frequency machine for edge sealing, the edges need to be cut with high quality on the cutting bed; 2. The tightness of the buckles must be moderate.
Process flow
Rough process: plastic sheet – cutting – sheet fixing – heating – forming – demoulding – edge removal – finished product
Material requirements for blister molding
- Blister molding can only produce products with relatively uniform wall thickness (generally the chamfers are slightly thinner), and cannot produce plastic products with widely varying wall thicknesses.
- The wall thickness of blister molding is generally within the range of 1 to 2mm or thinner (the most commonly used thickness of blister packaging sheets for small packaging is 0.15 to 0.25mm)
- The stretch degree of blister-molded products is subject to certain restrictions. The diameter-to-depth ratio of blister-molded plastic containers generally does not exceed 1, and in extreme cases it shall not exceed 1.5.
- The dimensional accuracy of blister molding is poor, and its relative error is generally more than one percent.
Method
Vacuum forming methods mainly include concave mold vacuum forming, punch vacuum forming, concave and convex mold vacuum forming successively, bubble vacuum forming, auxiliary punch vacuum forming and vacuum forming with gas buffer device.
Concave mold vacuum forming
Concave mold vacuum forming is the most commonly used vacuum forming method, as shown in Figure 1. Fix and seal the board (sheet) material around the top of the mold cavity. The heater heats the board (sheet) material until it softens [see Figure 1(a)], and then extracts the air in the cavity to form a vacuum, making the board ( sheet) The sheet) material is formed close to the mold cavity under atmospheric pressure [see Figure 1(b)]. After the plastic part is cooled and finalized, compressed air is introduced through the air extraction hole below to blow out the formed product [see Figure 1(b)]. c)].
The concave mold vacuum forming is suitable for products with a small depth. If the depth of the product is too large, the plastic plate (sheet) will stretch too much and the bottom will be too thin. The appearance and dimensional accuracy of the concave mold vacuum forming products are high.
Punch vacuum forming
As shown in Figure 2, the plastic plate (sheet) is clamped above the punch by the clamping frame and heated until softened [see Figure 2(a)]. Then the clamping frame moves downward, and the softened plastic plate (sheet) covers the punch like a tent, that is, it is cooled and loses its thinning ability [see Figure 2(b)]. Then the air between the plate (sheet) and the punch is extracted to form a vacuum, and the edges and surroundings of the plastic plate (sheet) are tightly attached to the punch and thinned to form [see Figure 2(c)]. The products formed by the punch vacuum forming method have high internal dimensional accuracy and the bottom is thick without thinning.
Punch vacuum forming is mostly used for thin-walled plastic parts with convex shapes, and the inner surface dimension accuracy of the molded plastic parts is high.
The concave and convex molds are vacuum formed successively
The convex and concave molds are vacuum formed successively as shown in Figure 3. First, the plastic plate is fastened to the die and heated, as shown in Figure 3(a). After softening, the heater is removed, and compressed air is blown through the male mold, while the female mold is evacuated to bulge the plastic plate, as shown in Figure 3(b). Finally, the punch is inserted downward into the bulging plastic plate and evacuated. At the same time, compressed air is passed into the die to make the plastic plate adhere to the outer surface of the punch to form, as shown in Figure 3(c).
This molding method blows the softened plastic plate to extend the plate before forming, so the wall thickness is relatively uniform and can be used to form deep cavity plastic parts.
Blowing vacuum forming
Some blister parts that require roughly uniform wall thickness can also be formed by blowing and vacuum forming. The mold structure is shown in Figure 4. Formed using a punch placed in a closed box. The sheet is first heated, as shown in Figure 4(a). Then compressed air is sent into the sealed box to blow the sheet outward, and then the punch is raised to form a sealed state with the sheet, as shown in Figure 4(b). Finally, the air holes on the punch are evacuated, and the outside atmospheric pressure is used to shape it, as shown in Figure 4(c).
This molding method is to thin all parts of the sheet at the same time in advance, so that the thickness of the plastic part is roughly the same during final molding.
Auxiliary punch vacuum forming
Auxiliary punch vacuum forming is divided into downward vacuum forming and upward vacuum forming.
Downward vacuum forming is shown in Figure 5. First, the plastic plate fixed in the concave mold is heated to a softened state, as shown in Figure 5(a). Then remove the heater and use the auxiliary punch to push down the plastic plate so that the air in the die is compressed. The softened plastic plate extends due to the thrust of the auxiliary punch and the movement of the enclosed air in the cavity, as shown in Figure 5 ( As shown in b), the concave mold is then vacuum formed.
Upward vacuum forming is shown in Figure 6. The advantage of upward vacuum forming is that the material does not contact the die during molding. The material expands and hangs after heating, as shown in Figure 6(a). At this time, the auxiliary punch rises upward and pulls the sheet into the initial shape without the concave die. This can make the thickness change of the sheet more uniform, as shown in Figure 6(b). If downward vacuum forming is used, the sheet first contacts the die, the contact point is cooled, the thickness no longer changes, and the molding effect is poor.
Simply relying on vacuuming and atmospheric pressure to form the sheet will cause uneven wall thickness of the plastic part due to the different deformation rates of each part. When the wall thickness is too thin, the plastic parts are often easily broken and lose their use value. Using auxiliary punch vacuum forming can improve the thinning of the bottom and corners of the plastic parts, as shown in Figure 7(a). The bottom and corners of deep-drawn blister are significantly thinned. As shown in Figure 7(b), in order to assist the vacuum forming of the punch, the thinning of the bottom and corner parts can be improved.
When the parison thickness is greater than 5mm. Auxiliary punch vacuum forming should be used. The thickness errors of plastic parts using different molding methods are shown in Figure 8.
Vacuum forming with gas buffer
As shown in Figure 9. This is a combination of plunger and compressed air. After heating the plastic plate and the frame, gently press it toward the die, then blow compressed air into the die cavity, blow the heated plastic plate, and the excess air escapes from the gap between the plate and the die. The heated air is blown from the top of the plate through the hole of the auxiliary punch. At this time, the plate is between the two air buffer layers, as shown in Figure 9 (a) and (b). The auxiliary punch gradually descends, as shown in Figure 9 As shown in (c) and (d). Finally, the blowing of compressed air into the auxiliary punch stops, and the concave mold is evacuated, so that the plastic plate is attached to the concave mold cavity and formed, and the auxiliary punch rises at the same time, as shown in Figure 9(e). The wall thickness of plastic parts formed by this method is more uniform, and deeper plastic parts can be formed.
Features
- Save raw and auxiliary materials, the product is light in weight, easy to transport, has good sealing performance, and meets the requirements of environmentally friendly green packaging;
- It can package any special-shaped products, and no additional buffering materials are needed for packaging;
- The packaged products are transparent and visible, beautiful in appearance, and easy to sell;
- The packaged products are suitable for mechanized and automated packaging, which facilitates modern management, saves manpower and improves efficiency.
Related concepts
Blister products
Blister products are processed with plastic. The product production principle is to heat and soften the flat plastic hard sheet material, then adsorb it to the surface of the mold with vacuum, and then cool it to form. Blister products are widely used and are mainly used in electronics and electrical appliances. Industry, food industry, hardware tools, cosmetics industry, toy industry, daily necessities industry, medicine, health care products, automobiles, stationery, cultural and sports supplies and other categories of industries.
Blister packaging
Blister packaging products mainly include: blister, tray, blister box, synonyms include: vacuum cover, blister, etc.
Bubble shell
The blister process is used to make transparent plastic hard sheets into specific convex shapes, which are covered on the surface of the product to protect and beautify the product. Also known as bubble cover, vacuum cover, plastic mask. According to the different forms of the bubble shell, it can be divided into: single bubble shell, double bubble shell, plug-in bubble shell and suction card bubble shell
Blister box
It is a kind of blister product with a cover and a bottom. The one with the bottom and the cover connected together is called a folding blister box, and the one with the bottom and the cover separated is called a bottom cover blister box.
Blister tray
Also called a plastic inner support, the plastic hard sheet is made into a plastic with a specific groove using a blister process, and the product is placed in the groove to protect and beautify the product.
Flocked inner support
It is a blister tray made of special materials. A layer of velvet material is glued on the surface of an ordinary hard plastic sheet, so that the surface of the tray has a velvet feel, which is used to improve the quality of the packaging.
Antistatic tray
It is a blister tray made of special material. The resistance value on the surface of the material is less than 10 11 ohms. Mainly used for blister trays for electronic and IT products.
Blister mold
Among the molds used in blister molding production, the lowest cost is the plaster mold, followed by the electroplated copper mold, and the most expensive is the aluminum mold. The mold is drilled with small holes for vacuum adsorption of heated hard sheets to form blister products.
