From the molecular structure point of view, the introduction of phenyl into the molecular straight chain of saturated polyester will improve its melting point, tensile strength and heat resistance, and the introduction of alkyl and ether bonds will improve its melt viscosity, flexibility and flexibility. However, this molecular structure also has high crystallinity and poor wettability and bonding strength. Therefore, it is usually necessary to add some other acids or alcohols to replace some of the original monomers during synthesis, so that they will undergo random polymerization, thus destroying high crystallinity and improving wettability and bonding strength. At present, 1, 4- butanediol is often added. By changing the proportion of components, polyester resins with different molecular weights and softening points can be obtained (see Table 9).
Table 9 Typical formulations of polyester resins with different softening points (molar ratio)
ingredient
Low softening point
Moderate softening point
High softening point
dmt
0.3
0.45
0.8
m-phthalic acid
0.6
0.45
0. 1
sebacic acid
0. 1
0. 1
0. 1
1, 4- succinic acid
2.0
2.0
2.0
Softening point (℃)
80-90
1 15- 125
185- 195
Construction melting temperature (℃)
90- 100
125- 135
195-205
The ratio of matrix and other additives of polyester hot melt adhesive is generally not very strict. The addition of additives is mainly to improve the melt viscosity of polyester resin. Commonly used diluents are polystyrene resin and petroleum resin, tackifiers are xylene resin and phenolic resin, and fillers are talcum powder and calcium carbonate. Sometimes in order to adapt to different working conditions, it is necessary to add reinforcing materials such as glass fiber and carbon fiber, flame retardants such as brominated aromatic compounds and phosphorus compounds, and ultraviolet absorbers such as benzophenone compounds.
Diluents such as PS resin and petroleum resin are often added to polyester resin, tackifiers such as xylene resin and phenolic resin, and fillers such as talcum powder and CACO3.
Hot melt adhesive is a kind of plastic adhesive. In a certain temperature range, its physical state changes with the change of temperature, but its chemical characteristics remain unchanged. Non-toxic and tasteless, belonging to environmental protection chemical products.
Hot melt adhesive bonding is to melt the hot melt adhesive by heating with a hot melt machine. The melted adhesive becomes liquid and is sent to the surface of the adhered object through the throat and spray gun of the hot melting machine. After the hot melt adhesive is cooled, the bonding is completed.
In order to give full play to the advantages of hot melt adhesive in spraying, it is necessary to use high-quality hot melt adhesive and corresponding hot melt adhesive machine with reliable quality and performance to match it.
In terms of hot melt adhesive equipment, cost and efficiency should be considered comprehensively when choosing hot melt adhesive machine. According to the speed requirements, automatic or semi-automatic glue spraying can be realized by using the production site, properly arranged hot melt adhesive equipment, throat, nozzle and supporting auxiliary equipment, so as to give full play to the advantages of hot melt adhesive and achieve maximum effect and economic benefits. In this regard, you can consult a professional hot melt adhesive machine manufacturer. Generally speaking, using automatic or semi-automatic glue spraying method, compared with manual method, the speed and cost advantages of hot melt adhesive in box sealing have been greatly exerted.