Study on Aluminized Composite Film Adhesive (I)

Abstract : The preparation and properties of new polyurethane adhesives for aluminized composite films are introduced. The adhesive has strong initial adhesion, high peel strength, and low residual solvent, and is suitable for a rapid aluminum-plating composite film production line.

Keywords: food packaging, polyurethane, adhesive, dry compound

Foreword

The aluminized composite film is a combination of aluminized films (VMPET, VMBOPP, VMCPP and VMCPE) and a plastic film to form a packaging material with aluminum luster. Because of its good barrier properties, puncture resistance, high and low temperature resistance, boiling resistance and opaque, impervious, and airtight, it has been widely used in food, health care products, pharmaceuticals and cosmetics and other packaging. In the past, the peeling strength of the aluminized composite film on the market was too low. In 1998, Beijing Gaomeng Chemical Co., Ltd. introduced the adhesive for YH501S aluminized film [1], which greatly improved the strength of the aluminized composite film, but there was plastic. Plastic composite strength is not as good as that of ordinary plastics, high system activity, inconvenient operation, and resistance to water boiling at 100°C. In order to meet the needs of the market, we redesigned the molecular structure based on the YH501S aluminum-plated film adhesive and developed a new type of adhesive for multi-purpose, high-strength, water-resistant boiled aluminum composite film.

1 Test section

1.1 The main raw materials

Dimethyl terephthalate, industrial grade, Beijing chemical plant; isophthalic acid, industrial grade, Yanshan petrochemical; adipic acid, industrial grade, Liaoning chemical plant; diethylene glycol, industrial grade, Jinshan Petrochemical; ethylene glycol , Industrial Grade, Jinshan Petrochemical; Diisocyanate, Industrial Grade, Bayer: Ethyl Acetate, Industrial Grade, Tianjin, Catalyst, Home Made; VMl0 Curing Agent, Homemade. 1# material is full-print BOPP film (20μ)/aluminum-coated CPP (VMCPP) film, which is provided by Qingdao factory; 2# material is full-print BOPP film (2811)/aluminum-plated CPP (VMCPP) film, Beijing Factory Provide: 3# material is full-print BOPP film (3511)/aluminum-coated CPP (VMCPP) film, Hebei factory provides;

1.2 Equipment and Instruments

HIROSHIMA laminating machine (Japan), compound speed 50 ~ 70m/min;

BLD-200s electronic peel tester.

1.3 Synthesis of Polyester Polyols

Measured dimethyl terephthalate, diethylene glycol and catalyst for transesterification reaction until the methanol to the theoretical amount, then add the measured isophthalic acid, adipic acid, ethylene glycol for esterification reaction After reaching the theoretical amount of water, the polycondensation was performed in a vacuum state. The acid value and hydroxyl value were sampled and analyzed at regular intervals. After passing, the polyester polyol was obtained with a molecular weight of about 2000.

1.4 Synthesis of Binders

The measured amount of polyester polyol, diisocyanate and part of ethyl acetate were added into the reaction kettle, and the temperature was raised to a certain temperature and kept at the temperature for several hours. Samples were analyzed for viscosity, solid content, and hydroxyl value. After passing the test, the temperature was lowered, and the auxiliary and acetate were added. The ester was stirred well to obtain the main adhesive agent. The trade name was YH5lSL.

1.5 Performance Test

1.5.1 Solvent Residue Test

According to YY0236-1996 drug packaging composite film (General) 5.5 solvent residue test.

1.5.2 Peel strength

According to GB2790-81, 180° peel strength was measured.

2 Results and Discussion

2.1 Adhesive Design Principle

Aluminized composite film is a composite aluminum film and plastic film together, the structure shown in Figure 1.

According to the diagram, it can be seen that the peel strength of the aluminum-plated composite film is mainly determined by the following factors:

1 adhesive body strength and the nature of the adhesive;

2 BOPP or PET film and adhesive interface strength;

3 adhesive and VM interface strength;

4VM and CPP or PET film interface strength.

The composite aluminum composite film was composited with ordinary two-component polyurethane adhesive. The peel strength of the composite film was very low at the VM-CPP interface, and the aluminum film was completely transferred. The 180° peel strength was less than 0.3N. This shows that the adhesive body strength, BOPP or PET film and adhesive interface strength, adhesive and state interface strength are higher than the VM and CPP interface strength. In fact, the interface strength between VM and CPP or PET film is much larger than 0.3N before the final composite. Therefore, the nature of the adhesive, that is, the nature of the adhesive, the composition of the adhesive, the molecular structure, the molecular weight distribution, and the residual amount of monomers have a great influence on the aluminum plating layer, and thus affect the peel strength and the residual amount of the solvent. If the molecular structure of the adhesive is unreasonable, the ratio of soft and hard segments is unreasonable, the molecular weight distribution is too wide, and the residual monomer content is high, not only affects the strength of the adhesive, the interface between BOPP and adhesive, the strength of the adhesive and the VM interface, but also affects the VM and CPP interfaces. Strength and residual solvent.

The two-component polyurethane adhesive is composed of a main agent comprising a hydroxyl group -OH and a curing agent comprising -NCO having an isocyanate group. When used, the main agent and the curing agent are mixed in a certain proportion, and after the molecules are extended by the chemical reaction, a high molecular weight polymer is formed. As an adhesive, the composition, molecular structure, and molecular weight distribution of the polyurethane have an important influence on the bonding. Polyurethane can be considered as a kind of block copolymer containing soft segment and hard segment [2]. The soft segment is composed of polyester, polyether, polyolefin and other oligomer segments, which is very compliant and shows random coiling state. Since the glass transition temperature is lower than room temperature, it is referred to as the rubber phase; the hard segment is composed of aromatic groups, substituted urea groups, carbamates, allophanates, biurets and the like, and is stretched at room temperature. Bar-shaped, it is not easy to change its conformational conformation, cohesive energy is large, and many microcells are associated with each other. As shown in Fig. 2, the glass transition temperature of these microcells is much higher than room temperature, and they are glass at room temperature. State, secondary crystal or microcrystal, called plastic phase. Due to the thermodynamic incompatibility of the two segments, microscopic phase separation occurs and phase or microphase regions form within the polymer matrix. The excellent properties of polyurethanes can be explained by the two-phase morphologies: the hard segments provide physical cross-linking of multiple functionalities, ie, the formation of hydrogen bonds and cross-linking, and play a reinforcing role: the soft segments are reinforced by the hard segments. Because the physical properties of aluminum, plastic film, etc. vary greatly, if the adhesive structure design is not reasonable, the stress generated during the curing process is concentrated; in addition, the two-component polyurethane adhesive is formed by the chemical reaction after the main agent and the curing agent are mixed. Molecular polymer (curing) bonding, this process takes a long time, usually requires 48h at room temperature. During this period, the residual monomers and small molecule oligomers in the adhesive will enter the interface between the VM layer and the CPP layer through the aluminum plating layer, and the VM layer will be reduced due to curing shrinkage of the adhesive and the stress caused by the aluminum and CPP wire expansion coefficients. The bond strength of the CPP layer.