Moisture-proof and Mildew-proof Polymer Composites

Chemical products such as gunpowder, explosives, primers, and other materials with high moisture absorption are prone to damp failure; electronic instruments and core plates, precision machinery, instrumentation, etc. are subject to moisture and rust or mold erosion. The national military standard GJB1444-92 stipulates that the water vapor permeability of packaging materials <3g·30d can meet the moisture-proof performance requirements of chemical products for packaging materials.
The production process of moisture-proof packaging materials should be designed according to the inherent properties of the polymer film and the moisture-proof mechanism. A biaxially oriented polypropylene (BOPP) film with good mechanical strength and good moisture resistance was selected. After vacuum aluminum plating, a PVDC (polyvinylidene chloride) emulsion with excellent moisture resistance was coated to obtain a composite material with excellent barrier properties. .
The vacuum aluminum plating process is to heat and melt aluminum metal to evaporation in a high vacuum state. The aluminum atoms condense on the surface of the polymer material to form a dense barrier layer—aluminum layer. Aluminizing process requirements: vacuum degree shall not be lower than 10-3Mpa, so as to avoid brown streaks or uneven thickness of aluminum layer; control the system tension, open the cooling system to avoid tensile deformation of the film by heat, and accurately control the take-up speed (280 ~320mmin), aluminum delivery speed (0.4~0.7mminΦ2mm aluminum wire) and evaporation boat heating current to obtain better aluminum layer thickness (250!! or more). Aluminum atoms block the voids in the molecular chain or between the molecular chains, greatly enhancing the water vapor barrier properties of the film.
PVDC emulsions are obtained by emulsion polymerization of vinylidene chloride and acrylic esters. The emulsion was coated on the surface of a VMBOPP (polypropylene aluminized) film, plasticized and crystallized into a high-barrier composite film. Coating process requirements: Anionic surfactants are used to adjust the surface tension of the emulsion around 40dyn c. The amount of diluent should not be too large to prevent poor drying; the coating thickness is in the range of 2.0 to 3.0 μm, and the infrared drying is set. The source step temperature ensures that the emulsion is sufficiently plasticized and crystallized; a small amount of anti-blocking agent is added to open the cooling system to prevent adhesion of the film; the curing chamber temperature is set in the range of 40 to 45° C. and the curing time is set to 36 to 48 h, making it crystallized and cured sufficiently. , to obtain excellent barrier steam performance. The moisture-proof polymer composite material formed through this process has a moisture permeability that satisfies the requirement of the National Military Standard GJB1444-92.
Precision machinery, chemical products, communication devices, instrumentation, etc. in the transport, use, storage process, in the appropriate temperature, humidity, nutrients, light, oxygen and other environmental conditions, prone to mold erosion. The national standard GB/T4768-95 “Moldproof packaging” stipulates that the anti-mildew packaging grade should be based on the product's anti-mold invasive ability, environmental conditions involved in transportation, storage, package structure, anti-mildew properties of the selected packaging materials, and the results of the mold test. And other factors to determine. The mold test was carried out according to the National Army standard GJB573A-98.305 under the specified temperature, humidity, strain, and test cycle.
In order to obtain certain mildew-proof properties, macromolecule materials must contain mold-repellent substances such as phenolic compounds, organometallic compounds, nitrogen-containing compounds, halogen-containing compounds, and sulfur-containing compounds in a certain proportion with thermoplastic resins such as polyethylene (PE). , Polypropylene (PP), polyvinyl chloride (PVC) mixed, and add a variety of additives, after mixing, plasticizing, granulation, obtained anti-mold resin. The carrier resin is made of low density polyethylene resin (LDPE) with good moisture resistance, low temperature resistance, easy heat sealing and chemical resistance, and the organic fungicide such as tributyltin chloride (10-25%) Add LDPE resin. The additives must be added in a certain order and thoroughly mixed. The selection of additives should pay attention to its synergy, compatibility with the resin and durability, and adapt to the process conditions. The use of mold-proof resin to produce mold-resistant polymer composites often uses the following two processes:
Three-layer (ABC) co-extrusion blow-dry compounding The anti-mold resin is extruded into the A fabric bucket. The process requirements: in the case of a good plastic film to ensure proper reduction of the extruder heating temperature in various areas; screw speed and heating temperature match; choose the right blow ratio, traction ratio; B, C fabric bucket selection of higher mechanical strength Low-density polyethylene resin (LDPE) and linear low-density polyethylene resin (LLDPE) with low content of slip agent. It should be noted that the MI (melt index) of the mold proofing resins, LDPE, and LLDPE should be as close as possible.
The C surface of the film was corona treated to give a wetting tension of more than 38 dyn/cm<2 > and dry compounded with the outer layer material. The mold composite polymer material was prepared by the dry-process compound process, and the A surface was used as a functional surface of the mold-proof material.
Double-sided (AB) co-extrusion compound The anti-mildew resin is extruded into the A fabric bucket. The process requires: selection of mildew resistance resin with high MI (around 7g/10min); proper adjustment of melt temperature near viscosity, prevention of deterioration due to excessive temperature; matching of screw rotation speed, heating temperature, and vehicle speed; proper addition of melt Body pressure, increase the filter layer or mesh number. The B fabric bucket is joined with grade 1C7A coating grade polyethylene (LDPE) resin. The surface of the material to be processed is coated with a polyurethane adhesive, which is then oven-dried and compounded with the B-surface. Select the appropriate solid content and the coating roller so that the amount of adhesive is 1-2g. Other processes require dry compounding. The antimold polymer composite material produced by the double-sided (AB) co-extrusion compounding process has the side A as a mold proofing function surface.
The moistureproof and mildewproof polymer packaging materials must also have sufficient mechanical strength to ensure that the products will not be damaged when they are squeezed, rubbed, bumped, shaken or dropped during stacking, loading, unloading, transportation and storage. Therefore, in the design process of product packaging, we must also use targeted materials and optimized combination of mechanical strength in order to enhance the overall performance of packaging materials.