Hot melt adhesive is a solid state of room temperature, heated to a certain temperature is melted into liquid, coated, moisturized by the adhesive, pressed, cooled, can quickly complete the glue. In most cases, hot-melt adhesives contain no water or solvents and are a 100% solid adhesive. Because of its low pollution, high initial viscosity and fast viscosity by the modern automation industry, in the book wireless binding, packaging seal, shoes, textiles and other aspects have been widely
. Hot melt adhesive according to its adhesive can be divided into ethylene-vinyl acetate co-polymelt hot melt adhesive, polyethylene and ethylene co-polymer hot melt adhesive, polypropylene hot melt adhesive, polyester hot melt adhesive, polyurethane hot melt adhesive, styrene hot melt adhesive and so on.
Polyurethane hot melt adhesives with polyurethane (PU) as the adhesive have excellent comprehensive performance compared with other types of hot melts, the main reason is that polyurethane hot melts lose the crosslinking produced by hydrogen bonds in the polyurethane molecule after heating, and become molten mucus, which is cooled and restored to its original properties. Therefore, polyurethane hot melt has excellent elasticity and strength, high bonding strength, solvent resistance, wear resistance, suitable for bonding a variety of materials.
PU hot melt is usually divided into two categories: one is the thermoplastic PU elastomer hot melt, and the other is reactive PU hot melt.
thermoplastic PU hot melt is the thermoplastic PU elastic system into the film, tape or glue end.
PU elastomers are line-type segment co-polymers produced by polyester polyols, isocyanates, and chain growth agent addition reactions.
by heating the melting glue and then cooling and curing and play a bonding role, but it itself has no reactive group, only hydrogen bonds to form intermolecules, resulting in low bonding strength, but also caused heat resistance, solvent resistance is poor.
wet solid reaction PU hot melt adhesive can overcome these shortcomings, performance can be comparable with solvent-reactive adhesive, so wet solid reaction PU hot melt adhesive since its inception in the 1980s, increasingly attracted the world's attention, become a leader in the adhesive industry.
present, the research and development of wet-solid PU hot melt in China has just started, pending in-depth and detailed application of basic research work to promote the process of wet-solid PU hot melt localization.
1 Experimental Part
1.1 Main Raw Materials and Equipment
Diphenyl Methane Diocyanate (MDI), Huntsman Products, USA; 30), Shanghai Gaohua three plant products; EVA, Shanghai Weisheng Packaging Materials Co., Ltd.; Petroleum resin C5, terpene resin, Shanghai Fangtian elastomer Co., Ltd.; Gumalong resin, Shanghai coking plant products; Songxiang GA90, Aokawa Chemical Co., Ltd. products. The coating machine and the heated reactor are all homemade. The stripping intensity tester uses the BLOD 200S type electronic peeling test machine produced by The Languang Electrical and Mechanical Technology Development Center in Jinan, Shandong Province. Coated substrates are made of commercially available canvas.
1.2 Experimental Method
1.2.1 Synthesis of MDI prepolymers
According to the experimental formula, the polyether is accurately weighed in a three-mouth can, stirred, heated, controlled at a temperature of 110 degrees C and vacuumed to remove moisture from the polyether. Cooling to 50 degrees C, into the N2 gas protection, add MDI, reaction temperature should be less than 100 degrees C, reaction 2h, vacuum to no bubbles, cooling, feeding.
1.2.2 Preparation of hot melt glue, hot melt glue joint
will add adhesive resin, thermoplastic elastomers, antioxidants and other raw materials into the reactor, stirring, heating, to be adhesive resin completely melted, vacuum, until no bubbles, add MDI prepopse prepared according to 1.2.1, stirring evenly. The coating machine is constant temperature, and the finished glue sample is evenly coated on the canvas, pressed, and made into an MDI-based wet-solid PU hot melt glue joint. Wet curing reaction occurs when placed at room temperature.
1.2.3 Test of the T-stripping strength of the glue connector
In reference to GB/T2791-1995, the test of the T-stripping strength of the glue connector is carried out on the BRD-200S electronic peeling test machine. The sample size is 2×25cm and the stretch speed is 25mm/min.
2 Results and discussion of the peeling strength test method of
adhesive is one of the important methods to study the adhesive bonding performance, which is suitable for the testing of flexible adhesive joints, which is mainly indicative of the adhesive joint's ability to resist crack expansion. There are many factors that affect the strength of adhesive peeling, such as the surface treatment of the adhesive, the curing conditions, the nature of the adhesive, the nature of the adhesive, the speed of peeling, the angle of peeling, etc. This paper mainly discusses the effect of the nature of PU hot melt adhesive itself on peeling strength.
2.1 Wet curing process
wet solid polyurethane adhesive is based on NCO end-based prepolymers, with thermoplastic resin, adhesive resin, antioxidants and other preparations. When the adhesive is heated, melted into fluid, coated on the surface of the coating, the two coatings are bonded, after cooling the adhesive layer condensation plays a bonding role, and then with the help of moisture in the air or attached to the surface of the adhesive and prepolymer end-NCO reaction, chain expansion, the formation of polyurethane-polyurethane structure of polymer polymer, further play a bonding role.
urethane chain (NHCOO) and arbond chain (NHCONH) are highly polar, forming a rigid chain link of polyurethane molecular structure, which makes the adhesive have high strength and heat resistance.
2.2 Effect of pre-polypulmer structure on the peeling strength of the glue joint
The isocyanate pre-polymer used in this paper was made using the reactions of polyether polyols and
. N220 belongs to polyether binary alcohol, and
reaction to produce pre-polymer of the line structure:
this paper uses the mixture of N220 and N330 as a polyol component to prepare the pre-polymer containing-NCO end base, aiming at the proper introduction of some cross-linking structure in the molecular structure of the line-type pre-polymer to improve the physical mechanical properties, heat resistance, solvent resistance of the glue joints, etc. The effect of the addition of N330 on the content of -NCO in prejudges can be found in Table 1.
can be seen from Table 1: With the increase of polyether 330 dosing, the content of -NCO in prejudes decreases. This is because N330 is a 3-degree polyether polyol, which reacts with MDI to form a branched or cross-linked structure. Wet-solid PU hot melts are made using MDI prejudgments with different -NCO contents, and their peeling strength values are found in Table 2.
can be seen in table 2
-polyether pre-ester structure has a greater effect on the peeling strength of hot melt gel. The peeling strength of a certain amount of N330 hot melt was significantly increased in pre-adhesive, but with the further increase of N330, the peeling strength of hot melt was reduced. This is due to the 3-degree N330 can react with MDI to produce pre-clusters of branched or cross-linked structures, improving the cohesion strength and mould of pre-accumulated matter, so that the adhesion strength of the hot melt joints with which it is the base material is increased. If the N330 is added too much, the cross-linking degree is increased, causing the brittleness of the glue layer to increase and the peeling strength to decrease.
2.3 Effect of adhesive resin on the peeling strength of the glue joint
Using the common hot melt adhesive adhesive resin, with thermoplastic elastomer EVA, preparation of wet-solid PU hot melt, study the effect of the type of adhesive resin on the peeling strength of hot melt. The pine resin is the earliest adhesive used, and it is also one of the most used adhesives in hot melt. From Table 3, it can be found that the pine GA90 resin is better than the terpene resin and gumalong resin for the addition of the hot melt system.
if a composite adhesive resin consisting of terpene resin and gumalong is used, the peeling strength of hot melt is 3.7 times higher than that of terpene resin and ancient marlon resin alone. This may be due to the synergy between the two adhesive resins on the strength of the adhesive. It can also be seen from Table 3 that the terpene resin is better than C5 petroleum resin for the addition of wet-solid PU hot melt. This may be due to the C5 petroleum resin is a straight-chain hydrocarbon polymer, and
-polyether prepolymer molecular chain contains aromatic structure, similar structure solubility, so the prepolymer and benzene-containing structure of the terpene resin solubility is good, resulting in the thermal melt system, terpene resin viscosity effect is better than C5 petroleum resin.
(1) In the synthesis of MDI-polyether pre-conjugation, with the increase of N330 dosing, the
free-NCO in MDI-polyether preheat is reduced;
(3) For this hot melt system, the viscosity of the pine resin is better than that of the terpene resin and the gumalong resin, and
(4) when the terpene resin and the gumalong resin are used together, the peeling strength of the canvas-canvas joint of the hot melt is nearly 4 times higher than when either of them is used alone.
source: Michaels Technology, inc.