1. PVC wood-plastic production process
PVC resin adding wood powder, calcium carbonate and auxiliary agent are mixed by a high-speed mixer to the required temperature, which is generally 115℃-125℃ according to the filling quantity, and then mixed to about 50-40 ℃ after natural cooling:
1, directly use the mixture of fine powder through the cone double extruder extrusion products this is a one-step method.One-step production has the advantage of no pelletizing, saving the investment of pelletizing equipment and the maintenance cost of water, electricity, labor and equipment, and reducing the loss of materials.But the quality and appearance of the products are not as good as the two-step method.Especially ecological wood is imitated wood for indoor and outdoor decoration needs to have the same wood grain that one step method is difficult (one step method can also produce wood grain such as density to do 1.0 or 1.2 above, but increase the cost).
2. The cooled powder is produced by tapered double pelletizing and extruded by single screw.The advantages and disadvantages are opposite to the above.The two - step method is ideal for ecological wood production.
Molding process and equipment
Good processing technology and equipment should ensure that materials and foaming agent mix evenly, and maintain a sufficiently high and stable head pressure, so that the pressure of the mouth mold is large enough and the pressure drops quickly enough, in order to obtain the bubble hole in good shape.
Mix and feed
Production technology of raw materials: wood fiber is the strong water imbibition material moisture content in 15% or more commonly, inorganic filler is around 5%, and the water content is of high and low impact especially wood plastic production stability and product quality of predators, such as impact foaming ratio, the bibulous rate of products, products of deformation, weather resistance and other physical properties.So it's best to keep it within 1%.Reasonable control the moisture content of fiber and packing -- -- -- -- -- to join high mixing machine -- -- -- -- -- in the mixing to 100 degrees -- - to join the right amount of coupling agent, mixed to 110-115 degrees, turn off the motor motionless mixer big open 2-3 minutes -- -- -- -- -- add PVC, stabilizer - mix to 80 degrees -- -- -- -- -- add lubricant additives and other -- -- -- -- -- 100 degrees and processing AIDS,Foaming agent ----120-125 powder discharge ---- after the powder discharge, the motor stops and then opens the big cover for 2-3 minutes and then mixes the next batch of material (it is better to mix the five hand material and clean the mixer) -- the powder in the mixing drum to make it to 40 degrees can be granulated or added to the twin screw production (the mixing drum must have circulating cooling water).In the mixing is must pay attention to observe the temperature and time as the general cold pot mixing raw material in 20-25 minutes or so, the hot pot in 12-15 minutes or so (the temperature is set to about 125 degrees), if the time difference is 3 minutes or more it may be the temperature line is wrong or the temperature control is not accurate, or the mixing machine horn knife wear is serious.This will affect the rate of foam stability, color.Granulation often to pay attention to the temperature control is accurate, the normal operation of the fan, the size of the current, particle size, surface, length of whether the material is sticky, feeding is stable, do not break the material.
The mixing process affects the dispersion of each component by affecting the contact and reaction between different components, and then affects the material properties.Mixing, should choose the appropriate feeding order, feeding temperature, feeding time.As the wood powder material is fluffy, the phenomenon of "building bridge" and "holding pole" is easy to appear in the process of feeding.Feeding instability will make the extrusion fluctuation, resulting in extrusion quality reduction, so it is necessary to make strict control of feeding method and feeding amount, generally using forced feeding device or hungry feeding, in order to ensure the stability of extrusion.PVC/ wood powder composite material extrusion foam molding is generally divided into two steps and one step process: two steps that is the first granulation after molding;One-step method eliminates the granulation process, and adopts the surface modified wood powder and PVC powder to be mixed at high speed and then directly added and extruded.The results show that the masterbatch method (two-step method) is beneficial to improve the mechanical properties of PVC/ WPC.
2. Molding temperature
Extrusion process:
Mainly pay attention to the following aspects
A. The key to setting the temperature of each section of the extruder is the compression section, the metering section and the mold.The accuracy of each temperature control such as temperature control is not allowed to affect the foam ratio and color.Foaming is mainly the setting of compression section and metering section temperature, molding is mainly the mold temperature.
B. Normal operation of each section of fan.
C. The magnitude and stability of the host current.If the main machine current fluctuation is large, it indicates that the lubricant. Processing AIDS. The dispersion between the fiber and PVC components is not very uniform.
D. The speed of the main engine must be kept the same, because the speed will affect the foaming rate and color.
The setting of extrusion molding temperature should take into account the physical action and chemical reaction of the material in the barrel of the extruder.The temperature of feeding section should not only ensure the material can melt quickly, prevent the escape of decomposition gas, but also prevent the foaming agent from decomposing in advance.The temperature setting of compression section and metering section should take into account the decomposition temperature and decomposition rate of chemical foaming agent, wood powder burning and PVC decomposition.The nose temperature should make the melt maintain good fluidity and at the same time have enough melt viscosity to keep the melt in the nose under high pressure and not foam in the nose.Yao zhuping thinks that low temperature extrusion should be used under the condition of full plasticizing.Screw and molding die and other equipment should also have low temperature extrusion characteristics to ensure that the bubble hole has a good shape and small diameter.The temperature of feeding section should be controlled below 165℃, the compression section and homogenization section should be between 160℃ and 180℃, and the head and die should be set below 160℃.
3. Screw speed
The influence of screw speed on extrusion foam is mainly reflected in the following aspects: first, the impact of extrusion pressure, the higher the speed, the greater the pressure in the extruder, so the more conducive to nucleation, nucleation of the number of bubbles, the higher the foaming rate.However, when the pressure is too high, the growth of nucleated vesicles is inhibited, which affects the full growth of vesicles.Second, the higher the screw speed is, the stronger the shear action is. When the shear action is too strong, it is easy to cause the bubble hole to merge or burst, which affects the quality of the foaming body and the formation of low-density foam plastics.Third, the screw speed is too high or too low, so that the residence time is too short or too long, easy to occur in advance of foaming or foaming agent decomposition is not sufficient phenomenon, is not conducive to the formation of uniform and fine bubble hole structure.Therefore, under the condition that other influencing factors remain unchanged, there is an optimal value of screw speed, which is generally between 12 and 18r/min.
4. Squeeze
Extrusion pressure is insufficient will cause products, surface roughness and low strength and high extrusion pressure can not only control gas head melt foaming in advance, and make the nose mouth mold inside and outside differential pressure big, so that the pressure drop rate is high, is advantageous to the bubble nucleation, increased the number of bubble nucleation, foaming rate increase, also is helpful to obtain even fine bubble pore structure.But too high extrusion pressure is not good for the growth of bubble hole.To obtain the appropriate head pressure, the screw speed, the head temperature and the shape of the die can be adjusted.
5. Molding equipment
The single screw extruder mainly transports materials by friction, the mixing effect is poor, the wood powder stays in the barrel for a long time, easy to burn, therefore, in the PVC/ wood-plastic composite material extrusion is more limited.In order to improve the mixing effect of PVC/ WPC, the single screw used for PVC/ WPC processing should be set up with mixing area, or granulated, and then extruded with granule, but this process consumes additives and reduces PVC performance.
5. Solutions to problems
The serial number
Abnormal phenomenon
why
The solution
note
1
Board face yellow
Insufficient stabilizer
Increased stabilizer fraction
Insufficient external lubrication and large friction cause material decomposition
Increase the score of outside slip
Setting the temperature too high
Reduce the temperature
2
The middle part of the plate is yellow
High local temperature setting of mold
Lower the temperature accordingly
Lack of outer slide
Increase the score of outside slip
The temperature in zone 5 of the extruder is high
Lower the temperature accordingly
3
Uneven plate thickness
Lip gap is unreasonable
Adjust die lip thickness
The choke block is improperly adjusted
Adjust the choke block
Outside the slide too much
Reduces the outside slip score
Slide in less than
Improved internal slip score
Unreasonable mold temperature setting
Adjust mold temperature
4
Plate brittle
Setting the extruder temperature too high
Reduce the temperature
The extruder temperature is set too low
Raise the temperature
Unreasonable formulation
Adjust the formula
5
The surface of the plate is not smooth
Lack of outer slide
Increase the score of outside slip
Insufficient processing AIDS
Score increase
Insufficient dispersion of fillers or auxiliaries
Adjust the content of fillers or additives
Mould temperature is set too low
Raise mold temperature
Temperature setting of extruder and mould is too high
Reduce the temperature
6
There are stripes perpendicular to the extrusion direction
The viscosity of foam conditioner is too high
Adjust the brand of foaming regulator
The extruder temperature is set too low
Raise the extruder temperature
Mould temperature is set too low
Raise mold temperature
Drag speed too fast
Reduced traction speed
7
There are large bubbles in the plate
Insufficient melt strength
Increase the dosage of foaming agent
The temperature in zone 5 of the extruder is too high
Lower the corresponding temperature
The corresponding mold temperature is high
Lower the temperature
There are impurities
Pay attention to raw material impurities
Back pad
Back to the flour
8
The plate bending
Unreasonable temperature setting of three rolls
Adjust temperature setting
The local temperature difference in the workshop is large or the air convection is too fast
Improvement of plant environment
9
Foam sheet foam hole
High extruder temperature setting
Reduce the temperature
Fewer foaming regulators
Improve the dosage
Improper lubrication adjustment
Adjust the proportion of
10
Sheet thickness is not easily controlled and moves back and forth
Outside the slide too much
Reduce the amount of outer slip
Mould temperature is not stable
Calibration thermometer to improve control accuracy
11
The sheet core part bubble hole is big, the surface bubble hole is small
High main temperature
Lower main engine temperature
Improper lubrication regulation
Adjust the proportion of
Insufficient melt strength
Add dosage of foaming regulator
Two, the shortage of PVC wood - plastic products
A discoloration problem
There are many causes of discoloration, such as ultraviolet light, temperature, humidity, air and the acidity of the product's environment.
How to prevent product discoloration:
A good color fastness, resistance to migration, high temperature resistance and heat resistance.
B choose a lubricant that is not easy to precipitate.
C add antioxidant, ultraviolet absorbent to improve the weatherability of the product.
D. Lower the processing temperature as much as possible to meet the processing requirements.
E product surface spray good weather resistance paint.
F. Materials with good weather resistance are co-squeezed.
B deformation problem
Deformation is mainly due to the low thermal deformation difference of vica of the product. To improve the thermal deformation, we mainly start from the following aspects:
A/add as little or as little as possible the additives that affect the deformation of the material, such as low melting point lubricants, CPE, DOP, epoxy soybean oil, etc.
B. Reasonable lubricating system and dosage.
C reasonable production process such as production speed, cooling water temperature.
D/reduce the internal stress in the product.
Reasonable design of e mold.
F. Placement and storage of semi-finished products.
In order to improve the relevant mechanical properties of wood-plastic, such as impact strength, bending strength, modulus, etc.
C flame retardant problem
The wood - plastic material group has the flame - retardant property.The key is to increase its oxygen index and reduce the amount of smoke emitted during combustion.Can be filled with flame retardants, plasticizers using chlorinated paraffin.
