Development of One-component Cross-linked Acrylate Pressure-sensitive Adhesive (I)

Introduction

Solvent-based acrylic pressure-sensitive adhesives occupy a very important position in the field of pressure-sensitive adhesives, and its market demand is second only to emulsion-based pressure-sensitive adhesives. The biggest disadvantage of acrylic emulsion pressure sensitive adhesives is poor water resistance and low temperature resistance, and the emulsifiers contained in the glue can also adversely affect the properties of the adhesive. In addition, the use (coating) of emulsion pressure sensitive adhesives is also affected by the stability of the emulsion. Solvent-based acrylate pressure-sensitive adhesives not only make up for the poor water-resistance and low-temperature resistance of emulsion pressure-sensitive adhesives, but also because they do not contain emulsifiers, solvent-based acrylate pressure-sensitive adhesives can often achieve unmatched performance of emulsion pressure-sensitive adhesives. . On the other hand, due to stability and particle size limitations, it is relatively difficult to adjust the adhesive properties of the emulsion pressure-sensitive adhesive, and it is much easier to adjust the performance of the solvent-based pressure-sensitive adhesive. For this reason, solvent-based acrylate pressure-sensitive adhesives are still widely used to make pressure-sensitive labels, BOPP packaging tapes, stationery tapes, and double-sided tapes.

The main factor affecting the performance of solvent-based acrylate pressure-sensitive adhesives is the size of the polymer molecular weight. To obtain good pressure-sensitive adhesive properties, it is necessary to increase the molecular weight of the polymer, but increasing the molecular weight increases the viscosity of the polymer solution. Especially during the polymerization process, an increase in the viscosity may cause the heat of the polymerization reaction not to be easily dissipated, thereby causing the explosion. On the other hand, excessive viscosity of the product can also affect the coating properties. Therefore, the molecular weight of solvent-based acrylate pressure-sensitive adhesives is generally relatively low. However, after the molecular weight is reduced, the properties of the adhesive will be greatly affected. In particular, the stickiness of the pressure-sensitive adhesive will decrease significantly. In testing the 180° peel strength, the glue tends to exhibit cohesive failure. In order to make up for this defect, a cross-linking agent is generally added to the front-end adhesive to increase the cohesive strength of the adhesive so as to improve the creep resistance and high-temperature resistance of the pressure-sensitive adhesive.

There are many ways to crosslink. In practice, the method of adding a cross-linking agent is mostly adopted, that is, the glue and the cross-linking agent are mixed before use in a certain proportion and then used. The viscosity of the adhesive to which the cross-linking agent is added gradually increases, and therefore, the glue added to the cross-linking agent must be used within a short period of time. In the actual production process, the pressure-sensitive adhesive must be prepared several times in accordance with the coating speed, which not only increases the workload of the workers but also causes quality problems. In order to solve this contradiction, researchers are trying to find a solution]. We have developed a one-component cross-linked acrylate pressure sensitive agent. By adopting appropriate protective measures, the cross-linking agent remains stable in the glue solution, and the cross-linking agent cross-links with the glue only under the effect of coating heating. The test results showed that the glue remained stable at room temperature for at least four months.

1 Test

1.1 Main test materials

Various acrylate monomers (industrial), ethyl acetate (industrial), crosslinker solution (self-provisioned).

1.2 Synthesis of Pressure Sensitive Adhesives

The solvent, monomer was charged to the reactor, heated to reflux, and the initiator solution was gradually added over 2.5 hours. After the initiator was added, the reaction was continued for 1 hour. The temperature is lowered to 50° C. and the cross-linking agent solution is added, and the mixture is stirred and mixed to obtain the product.

1.3 Performance Test

The glue was uniformly coated on a 28 micron thick BOPP film and the test pieces were tested after baking at 120[deg.] C. for 3 minutes. Dry glue thickness is 27μm, 180° peel strength is tested according to GB/T2792-81; initial viscosity is tested according to GB/T4852-84; viscosity is tested when tested according to GB/T4851-98; time is completely removed or 24 hours is displaced Distance indication.

2 Results and Discussion


2.1 Effect of Crosslinking Agent on the Properties of Pressure Sensitive Adhesives

The amount of cross-linking agent is an important factor in determining the performance of pressure-sensitive adhesives. From Table 1, it can be seen that as the amount of cross-linking agent increases, the peeling force and initial viscosity gradually decrease, while the holding viscosity gradually increases. This is because as the amount of cross-linking agent increases, the cross-linking density of the film increases, and the cohesive strength rises, so the holding viscosity increases.

2.2 The effect of temperature of the cross-linking agent on the properties of the adhesive

Table 2 shows the comparison of the properties of a crosslinker added at room temperature and a crosslinker added at 60°C. The results show that there is no significant difference in the adhesive properties when the cross-linking agent is added in two ways. This indicates that the cross-linking agent can be directly added into the reactor during the cooling period after the polymerization reaction is completed, thereby avoiding the preparation of the adhesive prior to use, thereby increasing the production efficiency.