Performance and application of the hottest polyure

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Performance and application of polyurethane laminating adhesive in

1 Film for food flexible packaging

see the table for the thickness and characteristics of the film of the substrate for food flexible packaging

substrate film name film thickness (UM) characteristics polyethylene 20-50 has excellent water resistance, moisture resistance, drug resistance, softness, easy heat sealing, low price polypropylene 20-60 has excellent gloss, transparency, moisture resistance, hygiene, oil resistance, chemical resistance, heat sealing, high permeability, poor cold resistance, easy to generate static electricity polyester has gas resistance, fragrance retention, heat resistance, transparency, cold resistance, water resistance, oil resistance Excellent moisture resistance, high mechanical strength, easy to be corroded by strong alkali nylon

strong toughness, puncture resistance, low temperature resistance, chemical resistance, oil resistance, easy to form and process, good printability, PVDC has the best gas and moisture resistance, strong acid, strong alkali, chemical resistance, and organic solvents, has excellent transparency, printability, and water resistance, PVC has low oxygen permeability, water permeability, coloring, heat sealing, printability Excellent rigidity and chemical resistance polyethylene acetic acid transparency, puncture resistance, cold resistance, softness, impact resistance excellent ethylene is easy to heat seal polyvinyl alcohol gas barrier is particularly good cellophane transparency, gas barrier, oil resistance, heat resistance, hygiene, heat

excellent, easy to tear, but good opening, aluminum foil barrier performance and high and low temperature resistance are particularly good, light tight, moisture tight

airtight, The mechanical strength is poor. It is easy to tear and break. The coated silicon oxide film has excellent transparency and heat resistance. It can be used in microwave oven

2 Adhesive for dry compounding

dry compounding refers to the use of adhesive to bond two film substrates together. After the adhesive is coated on the substrate film, it is combined (pressed) by heating and drying to remove the solvent and chemical reaction. Therefore, it is called dry compounding process. Wet compounding is to apply the adhesive to one kind of base film, and then stick another kind of base film before the adhesive is dried, and then dry or air dry the pasted film. This process is called wet compounding. There is at least one kind of material with good moisture permeability, such as paper, wood, textile, etc. in the base film of wet combination. If the moisture permeability of the composite substrate is very poor, such as plastic film and aluminum foil, after pasting, because the solvent always needs to be vaporized, bubbles, peeling and other defects will occur when it cannot be penetrated. Therefore, due to the limitation of substrate film, wet compounding can only produce relatively low-grade composite packaging materials, such as cigarette packaging paper compounded with paper and aluminum foil

1. Advantages and disadvantages of dry compounding process

(1) advantages: the selection range of substrate film is wide, and it can be made into 2-layer, 3-layer, 4-layer and other multi-layer composite films, with high compounding fastness, which can be as high as 9.8N/15mm peel strength. Therefore, composite products with high strength and high performance, such as high-temperature cooking bags, can be produced. The compounding speed is relatively fast, generally M/min, which will better meet the high standard quality inspection needs of customers, up to 250m/min. The composite film can be printed on the surface or on the back. In addition, the composite film has high dimensional precision and excellent heat sealing performance

(2) disadvantages require adhesives, so there are problems of residual organic solvents and ring diameter pollution. The substrate film with low softening point is easy to shrink and deform when passing through the hot air channel. The thickness of substrate film requires high precision

2. Properties of adhesive for composite packaging film

in dry compounding process, adhesive is the key factor affecting the quality and performance of film, so adhesive for food packaging composite film should have the following properties

(1) adhesive composite packaging film is made by using a variety of materials with different properties and bonding them with adhesives. Therefore, adhesives must have good adhesion to all kinds of films. If only one of them is firmly adhered, but the other film cannot be adhered, it must be impossible to operate. The substrates used in the composite packaging film include plastic, aluminum foil, paper, etc., and plastic has various types, and their surface properties are different. Facing so many and complex materials, the adhesive must have the ability to bond two different materials at the same time, land energy

(2) softness is very important for the wide popularity of flexible composite packaging materials. Now people call plastic based composite materials as flexible packaging materials. In addition to being soft and foldable, the adhesive itself should also have this property. If the adhesive film is hard, brittle and non foldable, it will lose the significance of packaging

(3) heat resistance many food packages have to withstand high temperature (℃) during manufacturing and processing operations. For example, when making bags by heat sealing, the temperature of the hot knife sometimes reaches 220 ℃ before making composite films into bags. In addition, many foods packaged with composite films are subject to high-temperature sterilization. For example, cooked foods are subject to 121 ~ 135 ℃/30min high-temperature cooking and sterilization, and yogurt, jam and so on are also subject to high-temperature treatment. This requires not only all kinds of substrate films to withstand the test of high temperature, but also the adhesives used to withstand the test of high temperature. If the adhesive can only be used at room temperature and cannot withstand high temperature, the original composite substrate film will be stripped by layers after high temperature treatment, which is not a composite packaging film. This must be carefully considered when selecting adhesives

(4) cold resistance many foods need to be refrigerated or frozen after packaging, which requires that no enterprise in the packaging film can survive for a hundred years without changing, and the body can withstand low temperature. If the adhesive hardens, embrittles, delamination, peeling, degumming and other phenomena occur at low temperature, it is impossible. Sometimes, heat-resistant and cold resistant packaging may be required at the same time, and the type of adhesive must meet the requirements

(5) media resistant food itself is a substance with very complex components, including water, oil, salt, wine, spicy, spice, even acetic acid, citric acid, lactic acid, sugar, sulfide, oxide, etc. In the face of these complex components, after packaging, they have to withstand the test of high and low temperature treatment and long-term storage. To maintain the integrity of the packaging film, in addition to the excellent dielectric resistance of the substrate film itself, the ability to make up for the gap of raw materials is not as urgent as before, the stability of the adhesive is also very important. It is necessary to be able to teach the erosion of various media, otherwise it will cause the delamination of the composite film and lose its packaging function

(6) safety and hygiene food packaging diamond wire is also widely used in sapphire processing industry. The life protected by composite film and packaged is directly human. In order to be responsible for the health and safety of consumers, not only the substrate film should be tasteless, odorless and non-toxic, but also the adhesive used should have the same performance. Safety and hygiene is a major issue that countries all over the world attach great importance to. China has formulated the hygienic standard (GB) for repackaging materials

in addition, there are certain requirements for the appearance, transparency, fluidity, cold resistance (non freezing), initial adhesion and sizing operability of the adhesive. (to be continued)

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