PVC film vacuum blister technology and use method

PVC film pressing technology is very important in the furniture industry, especially in the production of door panels and cabinets. Medium and high-density substrates are processed into various linear shapes and then blister-formed with various matt, high-gloss, color and texture PVC films, making the products colorful and dazzling, creating a lot of choice for consumers. However, products manufactured using this technology. Its quality varies greatly. The reasons for these differences are in addition to the factors of the base material and the facing material PVC blister film itself, the control of the process parameters during the processing is also very important. The following takes a certain type of imported positive and negative pressure vacuum blister machine as an example, using a two-component plastic absorbing machine imported from Germany to explain the entire process.

1. The working principle of the positive and negative pressure vacuum blister machine

　　Using the plasticity of the PVC film, through the adjustment and control of the film pressure time, the temperature in the equipment cavity and the air pressure, the PVC film is heated and pressurized, and the PVC is coated on the surface of the workpiece.

work process:

(1) The workpiece is placed on the workbench;

(2) The workbench enters directly below the heating plate;

(3) Close the heating plate and the workbench;

(4) The air between the heating plate and the silica gel film is drawn out, and the silica gel film is adsorbed on the heating plate to be heated;

(5) After the set time is reached, compressed air is injected between the heating plate and the silicone film, the silicone film and the PVC blister film are in close contact, the workpiece and the PVC blister film are heated, and the PVC blister film is softened, and the edge of the plate The temperature reaches the activation temperature of the glue;

(6) The air between the workbench and the PVC blister film is quickly drawn out to form a vacuum, and then compressed air is injected between the PVC blister film and the heating plate, and the PVC film is covered under the action of the set pressure and temperature. On the board.

2　 operating procedures

　　2.1　Use requirements for plastic suction

　　 absorbing plastic is a two-component glue, the activation temperature is about 60 degrees. The storage temperature must be between 5°C and 30°C, and flocculation may occur below 5°C. The plastic bucket should not be placed directly on the ground, but should be placed on a wooden bracket, especially in winter. The validity period of the blister is 6 months from the date of leaving the factory without opening the original packaging.

　　 plastic compounding ratio main agent: curing agent = 20:1, when the main agent is mixed with the curing agent, the main agent should be kept under stirring, and the curing agent should be slowly added and stirred for at least 3 minutes. The amount of glue prepared each time should be used up within 4 hours. The plastic bucket should be tightly closed after mixing.

　　2.2　 glue spraying process requirements:

　　2.2.1　The spraying sequence is end surface-front line type-front + line type-end surface, the plane part of it can be sprayed once; the end surface and the flat line type need to be sprayed twice.

　　2.2.2” The active time after mixing the main agent and the curing agent is 4-6 hours, and the glue-sprayed workpiece should be processed within 4 hours to obtain the best bonding effect. Otherwise, the activation temperature needs to be increased due to the cross-linking reaction of the glue. Although the glue effect is good from the appearance, the temperature resistance has been significantly reduced. If the glue is sprayed twice, glue marks will appear on the surface of the PVC film.

　　2.2.3　After spraying the glue, the surface is white and dry. It is not sticky to the hand or has obvious gloss after drying. The drying time is 30-50 minutes (depending on the temperature, humidity and spray quality of the environment).

　　2.2.4　A fan is usually used 1.5-2.0 meters away from the workpiece to aim at the workpiece and blow away the moist air to avoid PVC bubbling due to high humidity of the workpiece.

　　2.2.5　 In winter, in order to increase the temperature of the workpiece, a small holding room can be used to heat the workpiece to 20-25°C (it is forbidden to exceed 35°C, otherwise the workpiece will be deformed). Glue spraying should be carried out on a water curtain machine at an environment not lower than 16°C.

　　2.2.6　 glue spraying operator should wear a mask to protect the health of the operator.

　　2.3　 Use of Silicone Film for Blister Machine

　　 According to the characteristics of the workpiece line type (such as arc value, edge angle, line width and depth, etc.), choose different thickness of silicone film.

　　Silicone film is often heated and stretched, and its sag will increase. It should be installed in time according to the degree of sag of the silicone film to reduce the sag.

　　In order to prolong the service life of the silicone film and prevent the quality problems of the workpiece, the direction of use of the silicone film should be changed regularly, such as the front end to the back end and the left end to the right end.

　　 If there are holes or short cracks in the corners of the silicone film, it can be repaired with silicone and a patching machine. When repairing, the top is compacted with a flat heavy object. After drying for 24 hours, the repaired area can be used normally with 240# sandpaper.

　　2.4　 process parameter setting

　　2.4.1” Film pressure workpiece spacing: narrow and long workpieces with a width less than 10cm, the workpiece spacing is not less than 8cm; for workpieces with a width greater than 10cm, the workpiece spacing is not less than 6cm; the spacing between the workpiece and the worktable frame is not less than 8cm. The horizontal and vertical spacing should be in a straight line to reduce air flow resistance.

2.4.2 　 Workpiece backing plate: The width and length of the backing plate should be 6-10mm smaller than the width and length of the work piece. The edges and corners around the upper surface of the backing plate should be rounded with a radius of 3mm-5mm or a 3×45°C corner. , In order to ensure that the air between the PVC film and the workpiece is completely exhausted, so that the PVC film is firmly glued to the edge of the workpiece. The thickness of the backing plate should be about 3/4 of the thickness of the workpiece, which is one of the important measures to ensure that the PVC is not drawn white.

2.4.3 　 Set temperature: According to the different PVC film, the set temperature should be between 130℃ and 160℃. The temperature of ordinary PVC film (compared to high-gloss PVC film) should be higher, and the temperature of high-gloss PVC film should be lower (avoid Loss of light due to high temperature).

2.4.4 　 Setting time: preheating time should be between 30s-50s (different PVC film color, preheating time should be different, light color should be appropriately lengthened, dark color should be appropriately shortened; thick PVC film should be appropriately lengthened , The thin PVC film should be shortened appropriately), the vacuuming time should be about 8s, and the pressurizing time should be the preheating time plus 10 to 20s. The time to reach the set pressure should not be too long, it should be about 5s to ensure that the PVC film and the substrate are quickly adhered to the substrate when the end surface of the workpiece reaches above the activation temperature, and the PVC film on the workpiece is not excessively stretched (that is, no lines are eliminated) .

　　2.4.5　 set pressure: set the positive pressure to 3.8bar-4.2bar, and the negative pressure to 0.7bar-0.8bar, that is, positive pressure + negative pressure = about 4.5bar-5.0bar.

For over-thick workpieces, high-gloss PVC films and thin PVC films with a thickness of less than 0.3mm, the set temperature should be appropriately lowered, the preheating time should be appropriately increased, and the height of the entire bottom plate of the worktable should be increased to shorten the distance between the workpiece and the heating plate to reduce Or avoid the discoloration of PVC film.

　　When pressing veneer (wood veneer), use milky white latex adhesive, the temperature of veneer should not be lower than 105℃; the higher the pressure, the better, but the time to reach the set pressure is longer, that is, slow pressure.

　　2.5　 Trimming requirements

　　The workpiece processed by the press can be left for 20 minutes (to ensure the initial curing of the glue) before trimming.

　　 After trimming, scrape the edges and corners with special tools or chamfer the edges with 120#-180# sandpaper to make the PVC film lower than the surface of the workpiece. And use thinner such as alcohol to clean up the glue marks on the back. Check the quality when trimming, repair on-site if it can be repaired, and sort out those that cannot be repaired separately.

　　The work piece after film pressing should be placed face to face and back to back on a flat rack. A stack of 50 pieces, with heavy objects pressed on it to prevent deformation of the workpiece, and the storage time should not be less than 24 hours. It takes 24 hours for the film-pressed workpiece to reach the mid-term curing, and it takes 7 days to fully cure, so make sure that the workpiece is stored for more than 24 hours before packaging.

3　Temperature resistance test of film pressure workpiece

　　The temperature resistance performance of the film pressure workpiece can be checked through the temperature resistance test. The temperature resistance test must first collect the relevant parameters of the test piece, such as environmental parameters, process parameters, glue types (including activation temperature, factory date, number of glue spraying times), PVC film parameters (thickness, adhesive, manufacturer, etc.), processing time , Chen Fang time, etc.

　　 The temperature resistance test is carried out in a thermostat. The test temperatures are 40°C, 50°C, 60°C, 65°C, 70°C, 75°C, and 80°C. Put it at each temperature point from low to high for 1 hour, and then check whether the PVC film on the surface and edge of the test piece is peeled or open. If there is no peeling or open edge at the lower temperature, it will peel off when the temperature rises by one level. Or if the edge is opened, the temperature resistance of the test sample is one level lower. When a test piece is tested at 40℃ for 1 hour without peeling or opening of the PVC, and testing at 50℃ for 1 hour, the PVC is peeled or opened, then the temperature resistance of the test sample is 40℃.

4　The main causes of common quality problems

　　4.1 Wrinkles

(1) The distance between narrow and long workpieces is too small;

(2) The edges and corners around the upper surface of the backing plate are not chamfered;

(3) The horizontal and vertical spacing of the workpiece is not in a straight line, which increases the air flow resistance;

(4) The set temperature is too high;

(5) The time to reach the set pressure is too long.

　　4.2 Pull white

(1) The set temperature is too high;

(2) The time to reach the set pressure is too long;

(3) The line type is inappropriate.

　　4.3 The edges are not sticky:

(1) The quality of the glue is not good;

(2) The activation temperature of the glue is too high;

(3) The temperature of the equipment cannot reach the activation temperature required by the edge of the workpiece;

(4) The workpiece backing plate is not suitable;

(5) PVC adhesive performance is not good or no adhesive;

(6) The glue has expired or storage does not meet the requirements;

(7) Leaking glue or improper glue spraying method.

When quality problems occur, the processes or parameters should be adjusted one by one for the above reasons and recorded. Do not adjust multiple process parameters or processes at the same time, otherwise the real cause of the quality problem will be difficult to identify, and it will be difficult to formulate and adjust the production environment. Process standards provide an objective basis.

5 Conclusion

　　 The parameters provided above are based on relevant knowledge and operating experience. Due to differences in regions, equipment, working conditions, and materials, further tests are required, and process records are made at the same time to obtain process parameters that meet the quality requirements, and finally form process standards for operators to comply with. Although it is not convenient to directly test the bonding strength of the PVC film and the substrate after the PVC film is pressed, if the operation is carried out in strict accordance with the process standards suitable for the company's production environment, I believe that the final product can meet the quality requirements, which is also the important part of the process control method. .