Share hot melt adhesive film composition analysis, formula production process and technology development

Introduction: Hot melt adhesive has become the development direction of the adhesive market due to its advantages such as non-toxicity, low pollution, and convenient preparation. This article mainly introduces the background and classification of hot melt adhesive, focusing on the composition of EVA hot melt adhesive formula, as well as common products on the market, etc. The formula data in this article has been modified. If you need more detailed information, you can Consult our technical engineers.

EVA hot melt adhesive is widely used in mechanical packaging, furniture manufacturing, shoemaking, wireless binding, electronic components, and daily necessities bonding. Hechuan Chemical has introduced foreign high-end formula deciphering technology, specializing in component analysis, formula reduction, and R&D outsourcing services of EVA hot melt adhesive, and providing a full set of formula technology solutions for adhesive-related companies.

1. Background

Hot melt adhesive is a solvent-free solid adhesive made by melting and mixing thermoplastic resin or thermoplastic elastomer as the main component, adding plasticizers, tackifying resins, antioxidants, flame retardants, fillers, and other ingredients. mixture. Because of its non-toxic, no environmental pollution, easy preparation, and other advantages, it has become the development direction of the adhesive market. The world's annual output has been on an upward trend, and its speed is growing rapidly among various types of adhesives. The varieties are becoming more and more diversified, and their applications are becoming more and more popular. widely.

Ethylene and vinyl acetate copolymer (EVA) hot melt adhesive has a simple preparation method and is widely used in mechanized packaging, furniture making, shoemaking, wireless binding, electronic components, and daily necessities bonding. It has quickly become a widely used and large-scale hot melt adhesive. kind of. In 1960, DuPont of the United States realized industrial production and named the product Elvax. After that, UCC, USI, Bayer, ICI, Monsanto, and other companies successively produced such products.

EVA hot melt adhesive has high cohesion and low melting surface tension. It has a hot glue connection to almost all substances. It has outstandingly good chemical resistance, thermal stability, weather resistance, and electrical properties. It can bond quickly and has a wide range of applications. It is called "green glue" due to its non-toxic and pollution-free characteristics, which has attracted more and more attention.

Hechuan Chemical's technical team has rich experience in analytical research and development. After years of technology accumulation, it can use scientific instruments, a complete standard spectrum library, and a powerful raw material library to completely solve the problems encountered by many chemical companies in the production and research and development process, and utilize its eight major Service advantages enable enterprises to improve product performance and develop new products.

Sample analysis and testing process: sample confirmation-physical characterization pre-processing-large instrument analysis-engineer spectrum interpretation-analysis result verification-follow-up technical services. If you have any formulation technical problems, you can contact the Hechuan Chemical technical team immediately. We will provide enterprises with one-stop formulation technology solutions!

2. EVA hot melt adhesive

2.1 Composition of EVA adhesive

2.1.1 EVA resin

The main resin of EVA hot melt adhesive is ethylene-vinyl acetate copolymer (EVA), which is produced by high-pressure bulk polymerization or solution polymerization of ethylene and vinyl acetate. It generally has a random structure. The molecular structure, relative molecular mass, and distribution of the main resin EVA have a decisive influence on the bonding performance of hot melt adhesive.

1) Effect of vinyl acetate (VA) content

Since vinyl acetate (VA) is a polar group, as the content increases, the adhesion to the interface increases and the flexibility becomes better. However, VA itself has poor cohesive strength and dominates the strength of EVA. When the content exceeds a certain limit, the bonding strength will decrease. The lower the VA content, the higher the melting point and crystallization temperature; the lower the MI, the higher the melt viscosity). Therefore, the bonding performance of EVA hot melt adhesive is related to the vinyl acetate (VA) content in EVA. In this EVA copolymer, the VA content is usually 20%~30% (mass ratio).

2) The influence of the melt index

The melt index of EVA has a great influence on the bonding of hot melt adhesive. As the melt index increases, the melt viscosity of the adhesive decreases, which improves the fluidity of the adhesive and allows it to spread better on the substrate, thereby making The contact area between the hot melt adhesive and the substrate increase. However, the melt index reflects the size of the relative molecular mass. The melt index of EVA is too large, that is, the relative molecular mass is too small, and the cohesive strength of the hot melt adhesive itself is too small, resulting in a decrease in bonding strength; when the melt index is too small, that is, EVA has a relatively large relative molecular mass, and although its cohesive strength is high, it does not wet and spread well on the substrate interface, and the overall bonding strength depends on interface damage. Therefore, the melt index of EVA affects the bonding strength of hot melt adhesive. A melt index of 10~1000g/10min has better strength and toughness.

2.1.2 Tackifying resin

There are many kinds of tackifying resins. Their main function is to increase the wettability and binding force of the adhesive to the adherend, thereby improving

its bonding strength. The relative molecular mass of the tackifying resin is 10-10 000, and the softening point is 70-150°C. Tackifying resins are generally divided into four categories: ① Rosin and its derivatives, such as rosin glyceride, rosin phenolic resin, etc.; ② Terpene resin and its modifications; ③ Petroleum resin, the important ones are C5 and C9 resin and their hydrogenation Materials, mixtures and copolymers, etc.; ④ Oxygen indene resin and its hydride. When selecting a tackifying resin for hot melt adhesives, you should focus on its chemical composition, softening point, color, thermal stability, odor,

factors such as compatibility and price.

1) Rosin resin

The viscosity of the polymer is high when it melts, and the wettability and thermal adhesion to the adhered material are not good. Tackifiers can increase the wettability and bonding strength of the glue to the substrate, reduce the melt viscosity of the polymer, and thereby improve the bonding strength. As the amount of rosin added increases, the bonding performance of the EVA melt gradually improves. However, when the amount of rosin exceeds a certain value, the bonding performance decreases as the amount increases. This is caused by the decrease in cohesion of the hot melt adhesive system. Generally, the amount of rosin resin added: the total amount of EVA is about 10:6.

2.1.3 Petroleum resin

Petroleum resin does not have a fixed melting point, and its softening point becomes an important factor in determining the performance of the resin. Other physical properties such as melt viscosity and its compatibility with EVA, resin dosage, etc. have an important impact on the bonding performance of EVA hot melt adhesive [2 ~5]. The higher the softening point of the resin, the stronger the cohesive strength of the resin, the higher the adhesive strength, the higher the use temperature of the hot melt adhesive, and the wider its application range. It is hoped that the softening point of the tackifying resin should be as high as possible during use. However, an excessively high softening point may increase the melt viscosity of the resin and reduce the wetting ability of the hot melt adhesive, which is not conducive to the initial tack of the hot melt adhesive. Generally, the softening point of petroleum resin is generally between 90 and 110°C.

The melt viscosity of petroleum resin can affect the melt viscosity of EVA hot melt adhesive. Hot melt adhesive with low melt viscosity can spread better on the substrate, increase the contact area between the hot melt adhesive and the substrate, and improve the hot melt adhesive. The degree of infiltration of the adhesive into the adherend is conducive to improving the interface strength between the hot melt adhesive and the adherend; however, if the melt viscosity is too low, on the one hand, it may cause the filler in the hot melt adhesive system to settle, resulting in uneven distribution of material components. On the other hand, the cohesive strength of the hot melt adhesive may be reduced, which is not conducive to bonding. The melt viscosity of the added petroleum resin is preferably 150 to 250 mPa·s.

2.1.4 Wax

Wax is an effective viscosity regulator. Its main function is to reduce melt viscosity, improve fluidity and wettability, increase bonding strength, and prevent hot melt adhesive from caking. Increase surface hardness and reduce costs. Waxes can be divided according to their sources: ① animal wax (such as beeswax, etc.); ② plant wax (such as palm wax, etc.); ③ mineral wax (such as montan wax, etc.); ④ petroleum wax (such as paraffin wax, microcrystalline wax, etc.);

⑤Synthetic wax (such as polyethylene wax, Fischer-Tropsch wax, etc.). Commonly used ones are alkane paraffin and microcrystalline paraffin.

2.3.1 Paraffin wax

Paraffin wax is an effective regulator for the performance of hot melt adhesives. The melt viscosity of paraffin itself is very low, which can reduce the melt viscosity and surface tension of hot melt adhesives and improve the wettability and adhesion of hot melt adhesives to adhered metals and plastics. Thereby improving the bonding performance. At the same time, paraffin wax can also improve the wettability and low-temperature resistance of hot melt adhesive and reduce costs. Under normal circumstances, the appropriate amount of paraffin added is 20% of the total amount of EVA.

2.1.4 Antioxidants

The function of antioxidants is to prevent oxidation and thermal decomposition of hot melt adhesives. It is generally believed that hot melt adhesive is used in hot environments. When the thermal stability of components (such as alkane paraffin) is poor, it is necessary to add antioxidants. According to new research results, adding antioxidants can help improve the toughness, thermal stability, and service life of glue. Commonly used antioxidants include 2,6-di-tert-butyl-p-cresol.

2.1.5 Filling

Fillers are mainly used to reduce costs, reduce the shrinkage of hot melt adhesive when curing, change the crystallization speed, prevent glue penetration, and improve the heat resistance of hot melt adhesive. However, if the amount of filler in the hot melt adhesive is too much, the melt viscosity will increase, the wettability and initial tack will become worse, and the bonding strength will become lower. Commonly used fillers include calcium carbonate, kaolin, talcum powder, filled carbon black, etc.

Light calcium carbonate can be added as a filler to EVA hot melt adhesive. When the mass fraction is less than 10%, the cost can be reduced; when the mass fraction is greater than 10%, the shear strength decreases significantly.

2.1.6 Plasticizer

The function of plasticizer is to speed up the melting speed, reduce the melt viscosity of hot melt adhesive, and improve the flexibility and cold resistance of hot melt adhesive. Commonly used plasticizers include dioctyl phthalate and dibutyl phthalate.

3. Common EVA hot melt adhesive formula references

3.1 Recipe 1:

3.1 Recipe 2:

Thermoplastic elastomer SBS has many outstandingly good properties: high tensile strength, small deformation, good low-temperature resistance, etc. The addition of SBS helps EVA hot melt adhesives improve bonding performance and improve the cohesion of the adhesive.

By analyzing and restoring the formulas of chemical products, it is helpful for enterprises to understand the development level of existing technologies and know themselves and their enemies; it is helpful for independent innovation on existing products and obtaining intellectual property rights; it is helpful for discovering and solving problems in the production process. Through formula improvement and formula research and development of chemical products, enterprises can speed up product upgrading and enhance market competitiveness. Therefore, the analysis and research and development of chemical products have become urgent!