Solutions to Common Problems in Injection Molding of TPR Raw Materials
Source：德创化工Time：2020-03-16Hits：1916
First, is it harmful for TPR oil to come into contact with human body?
Answer: Usually the oil added to rubber is aromatic oil containing benzene ring, which is poisonous. However, the oil added in TPR is usually naphthenic oil or paraffin oil, and this kind of softening oil is usually straight-chain hydrocarbon compounds and is generally nontoxic. As long as you don't put it in your mouth and only contact with human body (skin), there is no side effect.
Suggestion: TPR adopts oil with good or bad quality, and inferior oil has great odor. It is suggested to choose low-odor secondary hydrogenation oil.
Can TPR be coated with metal?
Answer: Aluminum alloy and stainless steel cannot be directly coated with TPR. This is different from TPR plastic. However, with the further application of TPR, more and more products need to use TPR to encapsulate metal. There are two ways to wrap glue:
1. Direct "encapsulation"
That is, TPR is directly injected and coated on the metal surface without any third medium. However, the realization of this kind of encapsulation is closely related to the structure of the location where the metal pieces need to be encapsulated and the hardness of TPR.
The metal piece is integrally coated with glue, or the structure of the metal piece coated with glue has great curvature, or has holes, etc., which will strengthen the firmness of TPR coated metal piece; In addition, the higher the hardness of TPR material, the more compact and firm the bonding surface between TPR and metal will be.
2. Encapsulating with adhesive
In fact, more metal coating is applied locally. In order to ensure the firmness of the bond, it is necessary to use adhesive to achieve this.
The specific bonding process is as follows: firstly, the surface of the metal piece is treated to clean up dust and oil stains on the surface; Next, a suitable adhesive is selected and smeared on the surface of the metal piece; After the adhesive on the surface of the metal piece dries, the metal piece is fixed in a mold, TPR is injected onto the surface of the metal piece, and bonding and encapsulation are completed.
Analysis: If the adhesive is still liquid, it will be put into the mold for injection molding, and the adhesive will be removed from the surface of the metal piece. The adhesive dries, but it still needs to be sticky during high-temperature molding. The volatile adhesion of solvent is not good, and appropriate adhesive needs to be evaluated and selected. However, it is necessary to select the appropriate adhesive according to the characteristics of TPR materials.
Three, TPR products cracking is how to return a responsibility?
Answer: TPR product cracks are mainly caused by three reasons!
1. Cracking
The material is oxidized by air and ozone, resulting in aging and cracking. Some sheet products with low hardness and thin size (especially SBS substrate),
Exposed to the air, the surface will crack in a few days!
2. Solvent action fissure
Some toys that need to be sprayed with oil, as well as some soft shoes soles for children's shoes, sometimes the products will crack during processing. The reason for cracking is that the amount of ink or glue used is too large, or it is accumulated on the surface, but the surface of the product is corroded to cause cracking. Therefore, according to the different TPR materials, attention should be paid to the selection of adhesive, the amount of adhesive and the uniformity of surface spraying.
3. Stress cracking
TPR products are prone to stress concentration and notch effect due to structural design and some reasons, such as weld lines, uneven thickness of products and structures with obvious changes in angle or radian, thus causing cracks in products.
Four, TPR products gate peeling layered how to return a responsibility?
Answer: The internal cause is poor compatibility of materials. The gate location has strong shearing effect. The gate peeling delamination is mainly caused by insufficient material compatibility and strong shearing action.
Many TPR based on SBS system are alloy materials. If the compatibility of the system is not enough, peeling and delamination will easily occur at the gate position in case of special injection molding products (such as large flow length ratio and high firing rate).
At the gate location, because the flow direction and velocity of the melt will change dramatically, this kind of similar shearing action is a great test to the system uniformity of TPR melt. The larger the firing rate and the larger the flow length ratio, the more obvious the shearing action. If the compatibility of TPR components is not enough, it is easy to cause delamination and peeling of different phase structures and components.
Improvement: TPR compounding system should simplify the composition ratio and improve the compatibility of the system. High pressure and low firing rate shall be adopted as far as possible during molding. If possible, design a more reasonable inlet position to reduce the product flow length ratio.
