Discussion on the packaging technology of the hott

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Discussion on packaging technology of meat products II

(II) packaging materials and packaging methods

the purpose of packaging is to prevent bacterial contamination of products, so as to ensure product quality. Packaging can also play an advertising role, attracting the attention of consumers from Eastman's material portfolio, which is particularly suitable for small tonnage experimental occasions with variable functions. In all stages of manufacturing, circulation, sales and consumption, that is, from the factory to the hands of consumers, products always have to contact hands, so pollution may occur at any time, so we should prevent bacterial pollution through packaging

1. Performance of packaging materials

as the packaging of meat products, it must meet certain requirements. See table 2-1 for details:

most of the packaging materials used in meat products are plastic. Plastic has a wider range of packaging properties than paper, metal and other packaging materials. A packaging material can have several properties at the same time. Moreover, the lamination and pasting or coating technology of plastic thin glands can also supplement the insufficient performance of single films, and the lamination/coating technology can be used to develop films for various purposes

(1) oxygen isolation is the permeability of isolating oxygen. Not only oxygen, but also other gases. The amount of gas passing through the plastic film has nothing to do with the molecular size of the gas. Usually, it is carried out in two steps. At first, the gas is dissolved in the molecules of the film, and then infiltrated through diffusion. The oxygen resistance of the film is applicable to the packaging of all meat products except raw meat. Especially in vacuum packaging and inflatable packaging. Due to the role of oxygen, hemoglobin is changed into heme, causing product discoloration, promoting fat oxidation and the proliferation of aerobic microorganisms. Therefore, preventing the product from contacting with oxygen is extremely important for maintaining product quality and improving preservation

(2) moisture resistance is the property of blocking the passage of water vapor. When the film molecules do not contain hydrophilic hydroxyl and carboxyl groups, it is considered to have good moisture resistance. Moisture resistance changes greatly with temperature. The moisture resistance of the film is applicable to all meat products packaging. If the moisture of the product penetrates from the inside of the packaging film in the form of water vapor, or the product absorbs the water vapor from the outside, the flavor, organization and content of the product will also change. Especially for the packaging of dry sausages with little moisture, and to prevent the natural loss of quantitative products is extremely important

(3) shading, especially for light with 320 ~ 380 nm wavelength that has optical effect in ultraviolet light. This property is very important for vacuum packaged sliced products, colored products and smoked products. The transparent film has no effect of blocking ultraviolet rays. Although HDPE has some shading properties, the film is opaque. There are many ways to prevent ultraviolet transmission, one of which is to add ultraviolet absorbent to packaging materials. However, in recent years, the use of UV absorbers in food packaging materials has been banned. Therefore, a method of shading by using the properties of light has been developed. This method uses printing ink to absorb or reflect light, or satin processing roller to mechanically extrude concave convex patterns on the film surface to reflect light. When printing ink is used, black and white can absorb or reflect light. In addition, other inks, even with light and dark color difference, can not achieve the desired effect. Except for black, all light colors have almost no effect of absorbing light. Dark colors, according to black, blue, green and yellow, have poor shading in turn, while red and purple have no effect. Generally, when printing, the film with shading effect is opaque, and the disadvantage is that the products in the packaging bag cannot be seen. In order to make up for the defects of opaque films, a method of ultra micronization of ink has been developed recently, which uses the scattering of ultraviolet light with relatively short wavelength inside the film to block light, so that the longer wavelength visible light can pass through, and the printed film of the products in the packaging bag can be seen

(4) impact resistance this property is applicable to all packages. Especially for heavy things, tight packaging without gaps between casings and products is more important. The impact resistance of packaging materials can be ensured by the balance of tensile strength, tensile elongation and impact strength of materials. Such films include polyvinyl alcohol, polyvinyl chloride, polyvinylidene chloride, stretched nylon, etc

(5) cold resistance even at low temperature, the film will not be brittle, and can still maintain its strength and impact resistance. Generally, there is no problem in preserving meat products at -10 ~ 0 ℃, but if frozen meat products are preserved at -15 ℃, the cold resistance of the film must be considered, because it directly affects the sealing strength. Cold resistant packaging includes polyamide resin, polyethylene (low density), polyester, polypropylene (tensile), polypropylene (non tensile), etc

(6) heat resistance refers to the property of high softening point and no deformation even after heating (such as PVC). Since the product expands when heated, the heat-resistant strength of the film must be guaranteed. This property is suitable for packaging for secondary sterilization. Polyester, polyvinylidene chloride, polypropylene (no stretching), polypropylene (stretching) and polyethylene (high density) have good heat resistance

(7) formability refers to the property that the heated and softened film is blow molded (pneumatic forming) with air, or the film is formed along the forming die (forming along the product during compact packaging) by suction (vacuum forming). Good formability means that the four sides of the heated film can be stretched evenly with a small force. Once heated, the film can be stretched and enlarged immediately. When the heating temperature reaches a certain temperature, it will be in a stable state. The wider the stable temperature band is, the easier the film will be formed and the easier the packaging operation will be. For films with good formability, the influence of their barrier and sealing properties must also be considered. Films with these comprehensive characteristics are called composite films. Now the packaging films used in the market are mostly composite films. The formed films include non Stretched Nylon 6, non stretched polypropylene, polyvinyl chloride, polyvinylidene chloride, polyethylene, vinyl acetate copolymer, etc

(8) thermal shrinkage refers to the property that the film shrinks once heated. This property is suitable for degassing shrinkage packaging and vacuum packaging. By using the heat shrinkable property of the film, the product position in the fixed bag can be achieved and the preservation effect can be improved. Shrinkage refers to the property of the film given by stretching between moving molecules when the thermoplastic film is heated above the softening point temperature, that is, the restitution of the original state. When the film is stretched, the film is stretched thin, but the molecules in the film rearrange in the stretching direction. Therefore, its toughness, gas barrier and moisture resistance have also been improved. Polypropylene, polyester, polyvinyl chloride and polyethylene have good thermal shrinkage

(9) oil resistance is the property of preventing the free fat separated from the product from penetrating to the outside of the film. The phenomenon of fat components penetrating into the film may be caused by the following two situations: one is caused by the dissolution of the film, and the other is caused by fat infiltration. Oil resistance also has an impact on heat sealing. If the film is dissolved at the sealing place and there is penetration at the same time, this film is considered inappropriate. The so-called film with oil resistance refers to the film that is neither easy to dissolve nor easy to penetrate. The oil resistant film is suitable for the packaging of meat products containing fat. For example, polyvinylidene chloride, polyamide resin, polyester and other materials have good oil resistance

(10) when the thermal adhesive thermoplastic film is heated below the decomposition temperature, it will soften and its fluidity will also increase, becoming molten but in a short time. At this time, press the film tightly, and the molecules of the two films diffuse each other on the connecting surface. After it cools and injects a few drops of light lubricating oil into the lead screw, it solidifies and adheres. This property is affected by the melting temperature and viscosity of the film, pressing force and time. According to these effects, the bonding method and conditions also change. Ionic resins and ethylene vinyl acetate copolymers are materials with thermal adhesion. According to the temperature range, shrinkage and properties of the film, its bonding methods are also different, which are generally divided into hot plate bonding method (such as polyethylene, non stretched polypropylene, polyamide resin, polyvinyl alcohol, soft polyvinyl chloride, etc.), pulse bonding method (such as non stretched polypropylene, polyester, polyamide resin, etc.), high frequency bonding method

(11) slippage is the property that the friction coefficient between the membrane and the contact is small and easy to slide. This property is closely related to the opening of the film and the ease of machine feeding the film. When the friction is high, the film will be blocked when the products are bagged and continuously packed by the calendering film packaging machine

(12) during printing, when the temperature and humidity change, the size of the composite film can still maintain a relatively stable property. This property can ensure that the printing spacing is consistent, especially for stretch packaging machines, where the upper and lower film positions must be aligned, which is more important

(13) charged film is easy to absorb dust when it is charged, so there will be obstacles in the bonding of the film. The film surface with good insulation performance is almost charged. In order to prevent the film from being charged, you can add an antistatic agent, or install a discharge device on the film, add several kilovolts between the electrode and the ground wire, discharge from the needle, and ionize the air between the film and the electrode, so as to achieve the purpose of eliminating static electricity. Films that are difficult to charge are generally films that are not easy to absorb water. The films that are not easy to be charged include polyvinyl alcohol, polyvinyl chloride and cellophane. Polyethylene, polypropylene and polyester are easily charged films

(14) transparency the smaller the refractive index, the better the transparency of the film. The transparency of the film is expressed by turbidity. The smaller the value, the easier the light penetrates. Films with good transparency include extended polypropylene, extended polypropylene, low density polyethylene, high density polyethylene, polyvinylidene chloride, etc

(15) films with high gloss refractive index have strong reflection and good gloss

(16) deformation resistance is the property that the film is hard and elastic, and the film will not stretch even if the load is increased. The film with this property can be used in bag making machine and packaging machine, because this kind of film can meet the requirements of packaging machine. The film with high water absorption will weaken its deformation resistance in places with high relative humidity

in a word, the materials used in meat products packaging are required to have a variety of properties, but a certain kind of film can not meet all the packaging performance requirements, so we compound the films with various properties to make laminated composite films, which can meet the requirements of meat products packaging

(to be continued)

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