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Classification and application of TPU over-moulding
July 07 , 2021

TPU over-moulding mainly divided into bond with metal and bond with plastic.

TPU bond with metal is to encapsulate a layer of soft plastic on the metal surface. It make the surface of the metal features with anti-slip, shock-absorbing, anti-corrosion. There are generally four over-moulding methods in TPU overmoulding metal.
1. Block over-moulding
TPU block over-moulding has defect of poor bonding and unable to adhere. Over-moulding factory can make a hole in the metal part to strengthen the bonding.

TPU block over-moulding

2. Real over-moulding
TPU bond with resin, metal and other materials by the chemistry of them, such as the fluidity of the molecular hierarchical structure,the chemical reaction of polar group. It  generated firm bonding in the interface of the two materials.
As the chemical and molecular bonding of TPU and metal is greatly rely on the hardness of TPU, the hardness of TPU must be high in real over-moulding. In addition, the grooves and holes in metal surface make for stronger combination of TPU and metal.
3. Overall over-moulding
Overall over-moulding is wrap the whole metal parts with injection TPU parts. Usually the hardness of TPU used in overall over-moulding is relatively high and higher than 80A. It can’t be complete if there is only a part of metal been wrapped, that’s why it named overall over-moulding.  
4. pseudo over-moulding
TPU physically and mechanically bond with hard materials by the using of screw holes, grooves and other buckles. It is not chemical bonding of the two materials and they are bonded by adhesive.

Plastic bond with plastic is a unique Overmoulding. It can be either soft rubber coated hard rubber or soft rubber coated soft rubber.
1. TPU bond with rubber mainly divided into double-shot molding, two-step injection, Cladding extrusion.
double-shot molding is a overmoulding that processed by double coloured plastic injection machine. The double coloured plastic injection machine inject one of the rubber into shape and then inject another kind of rubber into the shape in the plastic injection cylinder corresponding mold cavity

Blending modification TPU

Blending modification TPU

2.Two-step injection is a overmoulding procession that inject one part of one material into shape in the injection machine. Then put this part as insert in another mould.

Polyester TPU

3. Cladding extrusion is a overmoulding procession that clad the fixed object with TPU by extrusion cladding. Cladding extrusion grant object better properties than itself. As to processed by cladding extrusion, the shape of object not only must be infinitely extended and must be strip-shaped, linear but also have a certain tensile strength and resistance to temperature as high as 230℃. It must be maintain the same thickness and size After high temperature processing
Overmoulding ribbon the typical TPU cladding extrusion is widely used to produce pets belt, motor car handle belt, drag hand belt, TPU trailer round belt; overmoulding linear is widely used to produce hanging rope,TPU round rope,TPU sub master tape and so on; overmoulding stripe is widely used in cladding metal line and is used to produce TPU core aluminium wire, TPU lamp (sets) and PU Metal wire (wire), etc.

TPU Material

Thermoplastic Polyurethane

What factor influence the TPU overmoulding process
1. Mold design: The surface of the mold should be frosted to facilitate demolding. Shrinkage rate of the TPU material must be take into account to avoid vacancies in rubber coating products
2. TPU material should be selected with appropriate hardness viscosity and crystallinity according to the product structure design
3. recommended molding temperature of TPU is generally to be 30-50°C.
4. The molding process generally adopts medium and high pressure slow burning rate control.
5. For products with thicker coatings is recommended to remove internal resistance to improve mechanical properties by post-annealing.
6. As TPU coatings are sensitive to oil stains, mold release agents and other additives on the mold surface. It is recommended to inspect and clean the mold surface   in time during the production process

How to choose TPU coating or TPE coating
1. Products that required good elasticity of coating layer and abrasion resistant recommend to choose TPU bond it.
2. Products required with high transparent coating surface is recommended to choose TPU

Disadvantages of TPU rubber coating ABS Compared with TPE coating ABS:
1 TPU is not as good as TPE in terms of tactile comfort and flexibility
2.Pure TPU is easier to sticky mold and more difficult demolding than TPE in terms of Injection molding
3.Hardness of pure TPU encapsulated ABS ranged from 60A to 90A while TPE encapsulated ABS can widely ranged from 20A to 90A.
Choosing TPU or TPE depends on the specific requirements of the customer. In genera TPE is more often used than TPU.

Hardness selection of TPU overmoulding
Hardness of TPU that encapsulated PP is about 65A-75A. Hardness of TPU that encapsulated PC, PA6, ABS is about 75A- 85A

Features of TPU overmoulding products:
1. Comfortable hand feeling, good covering with PC and ABS, great mechanical properties and high abrasion resistance.
2. Fast forming and good hand feeling;
3. Wear-resistant and scratch-resistant, scratch proof;
4. High anti-ultraviolet level, no yellowing after 96 hours

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