What you have to know is the common sense of TPE-coated adhesive materials
Source：德创化工Time：2019-12-25Hits：1906
TPE in elastomer industry refers to the composite functional material modified by SEBS. TPE elastomer soft adhesive has excellent comprehensive properties and is the most commonly used soft adhesive material for secondary injection molding, coating injection molding and two-color injection molding.
(1) The main advantages of TPE applied to the adhesive coating
1.TPE elastomer soft glue is applied to secondary injection molding, and is coated with glue and glued. Because TPE material has good skid resistance and good elastic touch, it can improve the touch feel of products and enhance the grip.
2.TPE elastomer soft adhesive can be adjusted to appropriate hardness (hardness range Shore 25-90A) and appropriate physical properties (such as abrasion resistance, scratch resistance, cohesiveness, melt index, etc.) according to the physical property requirements of the product. Various possible material application schemes are provided for different products.
3.TPE is coated with glue and shot-glued. Commonly used products such as handles, grips, electronic materials, etc. The material endows the product with comfortable tactility, improves the gripping property, improves the beauty of the product and the added value of the product. Most of the products are exported to the United States, Japan, European Union and other developed countries and regions. Because TPE elastomer soft adhesive is a green and environment-friendly raw material, the material does not contain phthalate and halogen, conforms to ROHS environmental protection testing standards, and fully meets the environmental protection requirements of developed countries and regions such as the United States, Japan, the European Union, etc.
(2) The main mechanism of TPE-coated adhesive bonding
TPE adhesive has the distinction of real adhesive and fake adhesive. True encapsulation uses the compatibility of soft glue and hard glue during softening and melting (compatibility mainly depends on the solubility parameter SP of the material. The closer the solubility parameter is, the better the compatibility of the two materials. For details about SP, refer to the knowledge of polymer chemistry). A layer of adhesive layer is formed on the contact surface of hard glue and soft glue, which greatly improves the adhesiveness of TPE soft glue and hard plastic. False encapsulation almost does not involve the compatibility of the two materials. The encapsulation of the materials enables soft and hard adhesives to be bonded together through mechanical force, through the design of molds and products and surface treatment, and through hoop embedding.
(3) TPE-coated glue injection bonding processing technology
In general, TPE injection molding adopts a secondary injection molding process, i.e. the hard plastic parts that have already been molded are fixed on the plastic coating mold, then soft TPE glue is injected and glued to the hard plastic parts at a suitable temperature, and the products are obtained after cooling. The injection temperature of glue coating is different according to the hard glue material. Due to the temperature, both hard glue and TPE soft glue should be softened to promote the compatibility of the two materials at the contact surface. In order to achieve the true encapsulation effect, the injection temperature of TPE encapsulated PP material is usually about 170-190 degrees Celsius. The encapsulated ABS material is about 220-220 degrees Celsius. The temperature of encapsulated PC is slightly higher than the injection temperature of encapsulated ABS. If PA nylon is coated, the injection temperature should reach 240 degrees Celsius.
(4) Common TPE-coated and adhesive materials
TPE is used for adhesive coating and shot bonding. TPE soft adhesive is used as the outer coating of soft adhesive. Common hard materials matched with TPE are mainly plastic, metal and woven fabric. TPE and woven fabric are mainly applied to luggage products. Like metal encapsulation, TPE and woven fabric are generally fake encapsulation. True encapsulation is commonly found in secondary injection molding and two-color injection molding, that is, the main material of TPE encapsulation is plastic. TPE can be firmly bonded with common general plastics PP,GPPS,HIPS,ABS and engineering plastics PC,PC/ABS,PA and their modified materials. The adhesion between TPE and POM polyoxymethylene is still a difficult problem in the elastomer industry. Because the solubility parameter SP(22.6) of POM is far different from that of TPE (7.2-7.6), the two materials are not compatible with each other, and no suitable compatibilizer has been found to promote the good adhesion between the two materials.
(5) Problems to be Paid Attention to in TPE Adhesive Injection Molding
● TPE compatibility between TPE and hard cementing components needs to be matched. The molecular solubility is close to each other, so the molecular compatibility is better.
● Sharp corners should be avoided as much as possible in the design to ensure excellent contact between TPE and hard rubber parts and improve bonding effect.
● Avoid leaving gas in the mold cavity through proper exhaust.
● Balance the thickness of TPE with the expected tactile sensation;
● Maintain the temperature of TPE melt to ensure bonding effect.
● TPE materials need to be baked and reprocessed for overmolding so as to reduce water lines on the product surface and obtain the effect of uniform surface color.
● The carrier resin of the selected color master batch is compatible with TPE and structural materials;
● Special treatment shall be given to smooth surfaces in order to increase the contact surface between soft glue and hard glue and strengthen the bonding effect.
●TPE should have good fluidity. Because the thickness to size ratio of TPE coating layer is very small, TPE usually needs to flow through a longer path and thin wall area to fill the mold.
● The flow length/product thickness ratio of ●TPE is less than 150: 1;
● Use good adhesive.
(6) Treatment of common encapsulation defects
Lacking glue-increasing processing injection molding temperature; Increase injection pressure; Improve material fluidity.
Split seam, overflow edge-reduce injection molding temperature; Increase the clamping force; Reducing injection pressure; Reduce fluidity from the perspective of formula.
The surface is pitted and not bright-increasing the injection molding temperature; Bake materials to reduce moisture content of raw materials.
Poor viscosity-sufficient baking before injection molding; Raise injection molding temperature; Adjust the recipe.
Injection Molding Deformation of Products-Strengthening Mold Cooling; Properly extend the mode locking time.
The product is stuck to the mold-add mold release agent or lubricant (for internal lubricant-mold release agent, attention should be paid to the added amount to prevent the release agent from separating out and migrating.
1. Sufficient injection temperature. Nylon and TPE plastic injection temperature should be above 190 degrees Celsius, preferably not more than 240 degrees. In particular, it is necessary to obtain the true encapsulation effect, because the softening temperature of nylon is 250-260 degrees. On the premise of ensuring TPE not to degrade, the closer the softening temperature of TPE and nylon is, the better the encapsulation effect will be.
2. The design of the structure of the encapsulated part of the product shall be as smooth as possible without obvious edges and corners, so as to increase the contact tightness between TPE and nylon hard glue.
3. Make some small holes in the unimportant positions of the nylon skeleton, or make some unsmooth surfaces to increase the contact area between TPE and nylon, so that TPE soft glue can be embedded into the nylon skeleton material through the small holes to achieve the hoop embedding effect. In fact, it is a combination of real package and fake package.
