First, ASA-PVC co-extruded WPC profile
ASA-PVC co-extruded wood is extruded from two extruders PVC wood-plastic substrate and ASA co-extruded coating material, and then through the coextrusion composite die, the ASA coating attached to the substrate with the extrusion The substrate surface, in order to achieve the purpose of covering the substrate due to the different raw materials used in the coating, co-extrusion coating performance is also different, the current co-extruded coating materials are mainly PMMA, PVC and ASA, Co-extrusion methods are as follows:
1. PMMA-PVC color coextrusion: refers to the exterior of the profile co-extruded layer of PMMA coating. PMMA is excellent weathering materials, and rich colors, decorative, good thermal stability, surface brightness, but PMMA brittle, bump or sawing incision easily lead to chunk cracks and chipping, the coating material has a lower drop impact weight.
2.PVC-PVC co-extrusion coating: refers to the dry mixing of PVC materials made of particles co-extruded pellets, this material due to poor aging resistance of PVC layer, easy to change color; but the modified PVC -PVC co-extruded coating also has good resistance to aging and weathering.
3.ASA-PVC co-extrusion: refers to the ASA coating material and PVC dry mix, the separate runner before leaving the die confluence, ASA melt in very thin thickness and PVC melt large area composite and together Extrusion die, and then stereotypes and cooling water tank stereotypes; after polishing, traction after the paste protective film, saw the final length of the final.
Second, the structure and performance of the ASA
ASA refers to a terpolymer of acrylonitrile (A), styrene (S) and acrylate (A) having the formula:
-CH2-CH (C5H5) -CH2-CH (CN) - 'n- or
-'-CH2-CH (C5H5) -CH (CN) -CH2-n-
ASA's performance characteristics can be summarized as follows:
1.ASA is an amorphous terpolymer that is a saturated backbone with no double bonds and is therefore very resistant to UV light. The carbonyl and nitrile groups in the macromolecular chains are highly UV resistant The benzene ring is a typical stable structure, it is difficult to photochemical reaction. Therefore, ASA has a strong UV resistance, color stability, excellent weather resistance.
2. Due to the introduction of acrylate rubber into the ASA structure, its copolymer has excellent impact resistance, especially low temperature impact resistance.
3. Due to the nitrile group contained in the ASA structure, it is highly resistant to chemicals.
4.ASA and PVC solubility parameters are very close, the two have good compatibility, rheological properties, thermal expansion coefficient closer.
5.ASA in the process of thermal stability, heat distortion temperature up to 92 ℃, co-extruded profiles and PVC profiles of the same strength welding.
Third, the configuration of co-extrusion equipment and requirements
Co-extrusion equipment
Co-extrusion machine is the main co-extrusion equipment, the general selection of single-screw extruder. Due to the complexity and variety of section profiles, co-extruded surface may appear in four directions up and down about, so require co- Flexible adjustment, the general choice of 45/25 single-screw extruder.
2. Co-extrusion mold
When designing the coextrusion die, the substrate and the co-extrusion layer must have the same flow rate in the shaping section and a certain compression ratio to ensure good coextrusion profile extrusion and uniform co-extrusion thickness.In China, ASA The design and manufacture of coextrusion molds are based on the experience of other coextrusion profiled molds.
3 co-extruded fittings
There are many differences in the production of ASA co-extruded WPCs compared to other coating materials, including the connection of the die to the coextrusion machine, the feeding of co-extrudates, etc. The quality of the products varies with the way they are used. In addition, due to the softer ASA coating co-extruding, the surface is prone to quality defects such as scratches in the co-extrusion production, making the surface gloss more difficult to control. Therefore, it is necessary to increase the light-adding / polishing equipment.
There are several ways to add light equipment: First, add heating equipment in the die forming place to increase the temperature of the ASA forming surface to improve the gloss and quality of the co-extruded surface; secondly, after the cooling and setting, add the polishing equipment and the ASA surface is polished , So that the surface quality is uniform, consistent luster. General lighting equipment has the following:
(1) heating rod: In the extrusion of the M-mode template along the co-extrusion surface to install a heating wire, just out of the extruded surface of the ASA material heating, improve ASA gloss.
(2) hot air: close to the extrusion template, the ASA surface with hot air heating, increase the surface gloss. By adjusting the amount of hot air to control the surface gloss.
(3) Polishing: After the profile is cooled and profiled, a polishing device is added to polish the ASA surface to make the ASA surface uniform in quality and consistent in gloss.
4. Co-extrusion connectors
Co-extruded connector is a coextrusion die connected with the coextrusion unit, basically designed in accordance with the design of the die interface, but found in use, some connectors inconvenient to use, difficult to disassemble, and some materials in the stream of poor flow, There are co-extruded connectors can not be heated, the flow channel is too long, the material has been cooled inside, is not conducive to ASA material forming and surface co-extruded surface finish. Therefore, the design of co-extruded connectors to note the following : The runner should be as short as possible, the inner wall should be smooth and smooth; the disassembly should be convenient and the operation should be facilitated; the heating ring should be equipped to control the temperature.
5. Co-extrusion feed method
Co-extrusion feeding methods vary due to the manufacturer's design, mold design should give priority to the co-extruded noodles, co-extruded noodles as far as possible in the design above, in order to observe the co-extruded surface of the surface conditions.Generally, co- Profile above, the use of the feeding method; co-extrusion side or below, the use of side feed. Side feed to choose the operator across the feed, or not easy to operate, co-extruded connectors can be classified according to different directions Processing, the above feed can be used as a co-extruded connector, the side of the feed is another kind of co-extruded connectors.
Co-extrusion die debugging
ASA co-extrusion die debugging according to the different mold structure using different methods, and some are the main ingredients, after the transfer ASA cladding material; and some must be transferred at the same time, which co-extrusion die head design.
(1) adjust the main material, after the transfer ASA coating material: In the initial mold test, no coating material, only the main profiles, to be section size basically meet the requirements, plus ASA coating material, adjust the total Squeeze the thickness and uniformity and debugging in place.
(2) the main ingredient and coating material at the same time transfer: This mold design features ASA material has independent flow channel, ASA material and the main ingredient is not the same time adding, the main material from the composite layer feeding chamber backwards, debugging When the first open the coextrusion machine, ASA should be filled with material flow channel and then squeeze out the main ingredient; or at the same time extrusion, and then adjust the main ingredient extrusion system, the material trimming to make the main material out of uniform, good cross-sectional size and then adjust ASA covering material, repaired co-extruded flow channel, so that the co-extrusion layer uniform .Finally, by adjusting the co-extrusion process parameters, the co-extrusion layer thickness to meet the quality requirements.
Fourth, the process and process points
1. Co-extrusion process flow chart:2 process points
2.1 raw materials processing
PVC wood plastic is made of PVC resin, wood flour, stabilizer, lubricant, filler, modifier, etc. It is the same as the general PVC mixing process. ASA material should be dried before processing to prevent the surface Occurrence of pitting, not only defects, drying conditions: 85 ℃ -95 ℃, 3-6 hours.
2.2 process conditions
(1) co-extrusion machineFifth, the production should pay attention to the problem
1. Raw material processing
ASA material must be dried, the first drying time to be slightly longer, not less than 4 hours. The choice of drying temperature according to the specific circumstances, the temperature is high, the time can be shorter; low temperature, the time may be extended , But the longest can not exceed 24 hours.
2. Surface scratches treatment
After the product is demolded, the surface of the ASA is not scratched and is very smooth and even; after cooling and setting, the powdery substance appears on the surface; after being completely cooled, obvious scratches will appear on the surface. In this regard, Within the relatively smooth, no right-angle transition joints, scratches less; stereotypes die shorter, less surface scratches, 2 stereotypes die products than 4 stereotypes die less product planning; the 4-stage stereotypes Mode 3 after the appropriate treatment, the production of almost no scratches the product, the surface conditions greatly improved.
3. Co-extrusion layer thickness control
The thickness of the ASA coextrusion layer is related to the weatherability, coverage and processing properties of the ASA coating and the thickness of the coextrusion layer is controlled by controlling the amount of extrusion from the coextrusion machine. ASA is extremely weatherable And PVC have a good compatibility, the combination of the two very solid, therefore, the general ASA co-extruded layer thickness of 0.2-0.3mm to meet the quality requirements. Thickness is too thin, some lighter colors will appear dew white; thickness too Thick, sometimes produced bending profiles appear, so control the thickness of the co-extrusion layer to ensure product quality is very important.
VI Conclusion
ASA-PVC co-extruded wood and plastic are also widely used in the fields of gardens, transport, construction, home improvement, vehicle interior and ship decoration, etc. With the global depletion of forest resources and the rising awareness of environmental protection, the wood-plastic industry has been well developed. How to further promote industrial development, improve technology, provide people with better wood-plastic products, these are as a wood-plastic people should be carefully considered questions.In my opinion, ASA-PVC co-extruded wood plastic in the specific technical issues , Such as raw material selection, process points, equipment configuration, mold design and other technical problems, we have to work together to solve.