Discussion on the packaging technology of the hott

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Discussion on packaging technology of meat products (Part 2)

(2) 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 and attract consumers' attention. In each stage of manufacturing, circulation, sales and consumption, that is, from the factory to the hands of consumers, the products always touch hands, so pollution may occur at any time. Therefore, we should optimize the experimental equipment to prevent bacterial pollution

1. the performance of packaging materials as the packaging of meat products must meet certain requirements

most of the packaging materials used for 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 laminating and pasting or coating technology of plastic thin glands can also supplement the insufficient performance of a single film. The laminating/coating technology can be used to develop a variety of films

(1) oxygen isolation is the permeability to isolate 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 effect of oxygen, hemoglobin is changed into hemin, which causes product discoloration, promotes fat oxidation and the proliferation of aerobic microorganisms. Therefore, it is very important to prevent the product from contacting with oxygen to maintain product quality and improve 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 product moisture passes through 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, it is very important to package dry sausage with little moisture and prevent the natural loss of quantitative products

(3) shading, especially for the light with 320 ~ 380 nm wavelength which 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 uses 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 if there is a color difference, can not achieve the desired effect. Except for black, all light colors have almost no effect of absorbing light. Dark colors are black, blue, green and yellow, and their shading becomes worse in turn. Red and purple have no effect. In general, when printing, the film with shading effect is opaque. The disadvantage is that the product 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. In the film, the scattering of ultraviolet light with relatively short wavelength is used to block the 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 applies 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. 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 to preserve 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). As the product expands during heating, 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 blown by air (air pressure forming), or the film is formed along the forming die (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 very small force. Once heated, the film will stretch and become larger. When the heating temperature reaches a certain temperature, it will be in a stable state. The wider the stable temperature band, 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. At present, most of the packaging films used in the market are composite films. The formed films include non Stretched Nylon 6, non stretched polypropylene, polyvinyl chloride, polyvinylidene chloride, polyethylene, vinyl acetate copolymer, etc

(8) heat shrinkability 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 shrinking property of the film, the product position in the bag can be fixed and the preservation effect can be improved. Shrinkage refers to the property that the film is given by the stretching between moving molecules when the thermoplastic film is heated above the softening point temperature, that is, the restitution to its 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 isolation 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 that fat components penetrate 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 penetration. The oil resistance also has an impact on the heat sealing. If the film is dissolved at the sealing position and there is penetration at the same time, it is considered that this film is inappropriate. The so-called oil resistant film 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 thermally bonded thermoplastic film is heated below the decomposition temperature, it will soften and its fluidity will increase, becoming a molten state. At this time, press the film tightly, and the molecules of the two films will diffuse each other on the connecting surface. After they are cooled, they will solidify and bond. This property is affected by the melting temperature, viscosity, pressing force and time of the film. According to these effects, the bonding methods and conditions also change. Ionic resin and ethylene vinyl acetate copolymer are materials with thermal adhesion. According to the different temperature range, shrinkage and properties of the film, the 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 PVC, etc.), pulse bonding method (such as non stretched polypropylene, polyester, polyamide resin, etc.) and high-frequency bonding method

(11) the sliding property is 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 force is large, the film will be obstructed when the product is 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 the stretch packaging machine, where the upper and lower film positions must be aligned, which is more important

(13) the 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, an anti electric agent can be added, or a discharge device can be installed on the film to add several kilovolts between the electrode and the ground wire to discharge from the needle, so as to 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. Easily charged films include polyethylene, polypropylene and polyester

(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 film can meet the requirements of the packaging machine. The film with high water absorption has weak deformation resistance at high relative humidity

in a word, the meat product packaging requires that the materials used in the "three-step" production process 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 product packaging$ Page break $

2. common packaging materials for meat products meat and meat products require different preservation and storage conditions due to different types. Therefore, there are many kinds of packaging materials used. According to the types of products, meat packaging materials can be divided into fresh-keeping packaging materials, low-temperature storage meat packaging materials and normal temperature storage meat packaging materials

(1) materials suitable for fresh-keeping packaging

① fresh-keeping film is generally an ultra-thin packaging machine made of single-layer polyvinylidene chloride 'target=_ Blank> transparent film. This film has high oxygen and humidity resistance, high heat-resistant temperature, and is easy to cut off when packaging. At the same time, the film itself also has strong adhesion and is easy to use. The tradition of Retailing in supermarket freezers

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