Summary
GWELL as manufacturer of extruders，TPU is a new type of environmentally friendly material. As TPU elastomer manufacturers continue to develop new products, some new TPU elastomers are gradually put into the market. Waterproof and moisture-permeable products are one of them, greatly promoting the development of waterproof and moisture-permeable TPU films. The film has the function of waterproof and moisture-permeable and is widely used in outdoor sportswear, medical accessories, surgical gowns, etc.
Brief description of TPU and its film
TPU is one of the fastest-growing new elastomer materials. In addition to its excellent characteristics such as environmental protection, high strength, high elongation, tear resistance, water resistance, oil resistance, wear resistance, etc., it can be processed using traditional processes such as injection molding, extrusion, casting, film blowing, etc., which further accelerates the development of TPU.
TPU film is an application of TPU elastomer, mainly used in various fields such as clothing, fabrics, shoes, life jackets, military tents, medical accessories, etc.
According to the type of material, TPU film can be divided into ordinary polyester type, waterproof and moisture-permeable polyether type, hydrolysis resistant polyether type, polycarbonate type, polycaprolactone type, polyolefin type, etc. In addition, each type of film also has matte, transparent, dyed, frosted, and other varieties.
Waterproof and breathable products are one of the fastest-growing varieties in the market in recent two years, commonly used 0.01mm, 0.012mm, 0.015mm these specifications, accounting for about 10%-15% of the market share of TPU film, with the development of the TPU market, and the gradual decline of prices, market share will have a large room for growth.
Preparation of breathable and moisture-permeable TPU film
1 .Drying of raw materials
Since the waterproof and permeable TPU absorbs water in the air very quickly, the drying of raw materials needs to be carried out using a dehumidifying dryer, the dew point is set at -40 ℃ ~ -30 ℃, the drying temperature is adjusted between 90 to 110 degrees for baking, generally need to be dried for 4 to 6 hours, moisture control below 300 ppm before production can be produced.
Normally, the raw materials dried by the dehumidifying dryer are left open in the air for 3 to 5 minutes, and the raw materials cannot be used because of moisture absorption, so the raw materials need to be conveyed in a closed pipe.
2. Mixing and requirements of raw materials
Waterproof and moisture-permeable TPU elastomer needs to be selected and then mixed with masterbatch, lubricant, matte additives, antistatic additives, and other processing aids, according to the actual needs of different products, adjust the appropriate proportion to mix, weigh the raw materials, stir and mix evenly through the mixer, add to the dehumidifying dryer for drying.
Some manufacturers also use machinery and equipment with multiple automatic weighing devices to dry and weigh various drying additives separately, then add them to the mixer of the extruder and feed them into the extruder through the screw of the extruder.
Because the waterproof and permeable film produced is very thin, the thickness of the film on the market is mostly between 0.01mm and 0.025mm, so the crystal point or glue point in the raw material should be within a controllable range, otherwise, in the produced film, there will be uneven dots, which leads to a series of problems such as broken film or low water pressure test of the film when compounding with the fabric later.
In addition, the TPU material itself has high processing viscosity, relatively poor film-forming property, narrow processing temperature range, and high requirements for the stability of the melting index of raw materials.
Film processing methods
There are many ways to process waterproof and moisture-permeable films, which should be selected according to actual needs.
- At present, the most commonly used method in the market is the double-layer co-extrusion blown film method, this method has high production efficiency, relatively stable product quality, thickness deviation is small; there are also very few manufacturers use the single-blown method to produce, but the single-blown method requires high equipment precision, processing environment temperature, air pressure in the membrane bubble, etc., production speed is relatively low 30% ~ 50%, but can save the cost of raw materials;
- Fewer manufacturers produce waterproof and moisture-permeable films by casting method, mainly due to low production efficiency, more scrap materials produced during production, and deviation in thickness control ability;
- There are very few manufacturers who dissolve TPU with solvents and then coat them to make some special products, but many of the products made by this method will have solvent residues, high cost, and are not environmentally friendly, and can only be used in some special fields.
Processing equipment
Depending on the processing method, there will be some differences in processing equipment. Commonly used processing equipment are film blowing machines, casting machines and coating machines. Due to some characteristics of TPU itself, the equipment required by the film blowing method and the equipment for processing PE film on the market have many details different, mainly blowing die flow channel and laminating line position, extruder screw, rotating device, winding device, cooling device, motor capacity and other major aspects, should be adjusted according to the characteristics of TPU raw materials.
The casting method mainly requires optimization adjustment in the TPU film extrusion line screw and cast film die.
The coating method usually dissolves raw materials with solvents such as DMF, EAC, TOL, MEK, etc., individually or mixed, and then coated by knife coating or roller coating.
Process control
The coating method is mainly to control the viscosity of the product after dissolution, the pressure of the knife and the coating surface, the gram weight of the coating, the production speed, the setting of the oven temperature, etc. If it is not well controlled, it will cause various problems such as uneven coating thickness and bubbles in the coating.