Membrane pressing process

Operating procedures
1、 Requirements for the use of film pressure adhesive
Membrane pressure adhesive is a two component adhesive with an activation temperature of around 60 ℃. The storage environment temperature must be between 5 ℃ -30 ℃, and flocculence may occur below 5 ℃. The rubber bucket should not be placed directly on the ground, but should be placed on wooden brackets, especially in winter. The validity period of the film pressure adhesive is 6 months from the date of leaving the factory without disassembling the original packaging.
Film pressure adhesive preparation ratio: main agent: curing agent=20:1. When mixing the main agent with the curing agent, the main agent should be kept in a stirring state, and the curing agent should be slowly added and stirred for at least 3 minutes. The amount of glue prepared each time should be ensured to be used up within 4 hours. After mixing the glue, the glue bucket should be tightly covered.
2、 Spraying process requirements
The spraying sequence is end face → front linear → front+linear → end face, and the flat part can be sprayed once; Two coats of spray are required at the end face and flat line.
The activity time after mixing the main agent and curing agent is 4-6 hours, and the sprayed workpiece should be processed within 4 hours to achieve the best bonding effect. Otherwise, due to the crosslinking reaction of the adhesive, the activation temperature needs to be increased. Although the bonding effect is good from the appearance, the temperature resistance has significantly decreased. If the adhesive is sprayed twice, it will show adhesive marks on the surface of PVC.
After spraying, the surface turns white and dry, and there is no stickiness when touched by hand or obvious gloss of the adhesive film after drying. The drying time is 30-50 minutes (depending on the temperature, humidity, and spraying quality of the environment).
The commonly used fan is 1.5-2.0 meters away from the workpiece and aimed at the workpiece to blow away moist air, in order to avoid PVC blistering caused by high humidity of the workpiece.
In winter, in order to increase the temperature of the workpiece, a small insulation room can be used to heat the workpiece to 20-25 ℃ (temperature exceeding 35 ℃ is prohibited, otherwise the workpiece will deform). Glue spraying should be carried out on a water curtain machine in an environment not lower than 16 ℃.
Glue spraying operators should wear masks to protect their physical health.
3、 The use of silicone film in membrane press
Select different thicknesses of silicone film based on the characteristics of the workpiece line shape (such as arc value, edge angle, width and depth of the line shape, etc.).
Due to frequent heating and stretching, the sagging degree of silicone film can increase. It should be installed in a timely manner according to the sagging degree of the silicone film to reduce sagging.
In order to extend the service life of the silicone film and prevent quality issues with the workpiece, it is necessary to regularly change the direction of use of the silicone film, such as changing the front end to the rear 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 using silicone and a film repair machine. When repairing, compact the top with a flat heavy object, dry for 24 hours, and then use 240 # sandpaper to level the repair area for normal use.
4、 Setting of process parameters
The spacing between film pressing workpieces: for narrow and long workpieces with a width less than 100mm, the spacing between workpieces should not be less than 80mm; For workpieces with a width greater than 100mm, the spacing between workpieces shall not be less than 60mm; The distance between the workpiece and the workbench frame shall not be less than 80mm. The spacing between the horizontal and vertical directions should be in a straight line to reduce the resistance of air flow.
Workpiece backing plate: The width and length of the backing plate should be 6-10mm smaller than the width and length of the workpiece. The edges and corners around the upper surface of the backing plate should be rounded with a radius of 3mm to 5mm or rounded with a radius of 3mm to 5mm × 45 ℃ angle to ensure that the air between PVC and the workpiece is thoroughly extracted, achieving the effect of PVC firmly bonding 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 PVC is not pulled white.
Setting temperature: According to the different types of PVC, the setting temperature should be between 130 ℃ -160 ℃. The temperature of ordinary PVC (relative to high gloss PVC) should be higher, and high gloss PVC should be lower (to avoid loss of light due to excessive temperature).
Setting time: The preheating time should be between 30s and 50s (depending on the color of PVC, the preheating time should also be different. Light colored PVC should be appropriately extended, dark colored PVC should be appropriately shortened; thick PVC should be appropriately extended, and thin PVC should be appropriately shortened), the vacuum pumping time should be around 8s, and the pressurization time should be around 10-20s plus the preheating time. The time to reach the set pressure should not be too long, it should be around 5 seconds to ensure that the PVC on the workpiece end surface quickly adheres to the substrate and does not excessively stretch the PVC on the workpiece when it reaches the activation temperature.
Set pressure: Set the positive pressure to 3.8-4.2bar and the negative pressure to 0.7-0.8bar, that is, positive pressure+negative pressure=about 4.5-5.0bar.
For excessively thick workpieces, high gloss PVC, and thin PVC with a thickness less than 0.3mm, the set temperature should be appropriately reduced, the preheating time should be appropriately increased, and the height of the entire bottom plate of the workbench should be increased to shorten the distance between the workpieces and the heating plate, in order to reduce or avoid PVC discoloration issues.
When laminating wood (veneer), use milky white latex adhesive, and the temperature of the veneer should not be lower than 105 ℃; The greater the pressure, the better, but the time to reach the set pressure should be longer, that is, slowly pressurize.
5、 Edge trimming requirements
The workpiece processed by the press should be left for 20 minutes (to ensure initial curing of the adhesive) before edge trimming can be carried out.
After trimming, use a special tool to scrape the edges or chamfer with 120 # -180 # sandpaper to make the PVC lower than the surface of the workpiece. And clean the adhesive marks on the back with thinner such as alcohol. Check the quality during edge trimming, repair the parts that can be repaired on site, and select and handle the parts that cannot be repaired separately.
The workpiece after membrane pressing should be placed face to face and back to back on a flat material rack. 50 pieces per stack, with heavy objects pressed on top to prevent deformation of the workpiece. The storage time should not be less than 24 hours. The time for the membrane pressed workpiece to achieve mid-term curing is 24 hours, and complete curing takes 7 days. Therefore, it is necessary to ensure that the workpiece is aged for more than 24 hours before packaging.
6、 Temperature resistance test of membrane pressure workpiece
The temperature resistance performance of membrane pressed workpieces can be tested through temperature resistance tests. The temperature resistance test first needs to collect relevant parameters of the test piece, such as environmental parameters, process parameters, adhesive type (including activation temperature, factory date, number of adhesive sprays), PVC parameters (thickness, adhesive backing, manufacturer, etc.), processing time, aging time, etc.
Conduct temperature resistance tests in a constant temperature box at temperatures of 40 ℃, 50 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃, and 80 ℃, respectively. Place it at each temperature point from low to high for 1 hour, and then check whether the PVC on the surface and edges of the test piece has peeled off or opened edges. If the lower temperature has not peeled off or opened edges, but when the higher temperature has peeled off or opened edges, the temperature resistance of the test sample is the lower temperature. If a test piece is tested at 40 ℃ for 1 hour without PVC peeling or edge opening, and at 50 ℃ for 1 hour with PVC peeling or edge opening, the temperature resistance of the test sample is 40 ℃.
7、 The main causes of common quality problems
1. Pleats
(1) The spacing between narrow and long workpieces is too small; (2) The edges and corners around the upper surface of the base plate are not chamfered; (3) The distance between the horizontal and vertical directions of the workpiece is not in a straight line, which increases the resistance of air flow; (4) The set temperature is too high; (5) The time to reach the set pressure is too long.
2. La Bai
(1) The set temperature is too high; (2) The time to reach the set pressure is too long; (3) The line type is not suitable.
Edge not firmly adhered:
(1) The quality of the adhesive is not good; (2) The activation temperature of the adhesive is too high; (3) The temperature of the equipment cannot reach the required activation temperature at the edge of the workpiece; (4) Improper workpiece pad; (5) Poor or no PVC backing adhesive performance; (6) The adhesive has expired or does not meet the storage requirements; (7) Leakage or improper spraying method.
When quality problems occur, the process or parameters should be adjusted one by one based on the above reasons and recorded. It is strictly prohibited to adjust multiple process parameters or processes simultaneously, otherwise the true cause of quality problems will be difficult to identify, and it is also difficult to establish and adjust process standards for the production environment to provide objective basis.