CN111002672A - Plastic sheet for packaging frozen food and preparation method thereof - Google Patents
Plastic sheet for packaging frozen food and preparation method thereof Download PDFInfo
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- CN111002672A CN111002672A CN201911277963.5A CN201911277963A CN111002672A CN 111002672 A CN111002672 A CN 111002672A CN 201911277963 A CN201911277963 A CN 201911277963A CN 111002672 A CN111002672 A CN 111002672A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
- B29D7/00—Producing flat articles, e.g. films or sheets
- B29D7/01—Films or sheets
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
- B65D65/00—Wrappers or flexible covers; Packaging materials of special type or form
- B65D65/38—Packaging materials of special type or form
- B65D65/40—Applications of laminates for particular packaging purposes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2307/00—Properties of the layers or laminate
- B32B2307/50—Properties of the layers or laminate having particular mechanical properties
- B32B2307/558—Impact strength, toughness
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2307/00—Properties of the layers or laminate
- B32B2307/50—Properties of the layers or laminate having particular mechanical properties
- B32B2307/582—Tearability
- B32B2307/5825—Tear resistant
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2323/00—Polyalkenes
- B32B2323/10—Polypropylene
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2553/00—Packaging equipment or accessories not otherwise provided for
Abstract
The invention belongs to the technical field of food packaging materials, and particularly relates to a plastic sheet for frozen food packaging and a preparation method thereof. The invention relates to a plastic sheet for packaging frozen food, which is prepared by extruding inner layer materials, middle layer materials and outer layer materials through a three-layer co-extrusion forming machine set; the middle layer is prepared by mixing polyurethane-loaded silicon dioxide aerogel and polypropylene powder; the inner layer and the outer layer are respectively prepared by mixing polypropylene, propylene-ethylene block copolymer and compatilizer. The plastic sheet for packaging frozen food has good flexibility, improves the low-temperature brittleness of the polypropylene sheet, has good mechanical property under the low-temperature freezing condition, avoids tearing and brittle fracture caused by the low-temperature brittleness, and is particularly suitable for packaging large articles in cold regions and ultra-low-temperature storage and packaging of frozen food.
Description
Technical Field
The invention belongs to the technical field of food packaging materials, and particularly relates to a plastic sheet for frozen food packaging and a preparation method thereof.
Background
The frozen food is prepared by processing qualified food materials, rapidly freezing at-30 deg.C, packaging, and storing at-18 deg.C or below. Because the whole process adopts low-temperature cold chain preservation, the frozen food has the characteristics of long shelf life, difficult deterioration and convenient eating, but also provides greater challenges and higher requirements for packaging materials. Basic requirements for frozen food packaging: the quality and the characteristics of the product are kept from production, transportation to sale, the bacterial pollution is prevented, and the eating is convenient. For this purpose, the packaging material must have the conditions: has certain mechanical strength (high and low temperature resistance); barrier properties (high barrier to gases and liquids); resistance to contents (acid, oil resistance); sanitation; and (4) operation resistance.
At present, there are two main types of packaging for frozen foods: a soft type and a hard type. The flexible type is based on plastic films. The former is a large proportion of thick and hard packages, such as paper packaging boxes with a larger thickness, composite aluminum foil stamping containers and the like.
Among the hard types, such as food grade plastic sheets, common food grade plastic sheets are: PET plastic plate, PP plastic plate, HDPE plastic plate, LDPE plastic plate, PS plastic plate, PC plastic plate, PVC plastic plate, BOPS plastic plate. The PP plastic plate is one of common plastics, can be made into food plastic bags, food plastic boxes, food straw and other food plastic packages, and is safe, non-toxic, low-temperature resistant and high-temperature resistant. PP is the only plastic which can be heated in a microwave oven, has high strength and folding resistance, and cannot be damaged when falling from high altitude for 50000 times to 20 ℃. Food-grade PP sheet is commonly used for plastic packaging of frozen dumplings and microwave heating food.
The polypropylene (PP) material has the characteristics of no toxicity, no odor, high light transmittance, good glossiness, good solvent resistance, high stiffness, good heat sealing performance and the like, and is widely used for packaging foods, tea leaves, medicines, sanitary products, clothing, stationery, daily necessities and the like. Although PP has many excellent properties as a packaging material, the most prominent defects are large low-temperature brittleness and low tearing strength, and the tearing or brittle fracture phenomenon of PP blown films or extruded sheets often occurs during the packaging of large articles in cold regions in winter and the ultralow-temperature freezing and packaging and storage of foods, so that the application field of PP is limited.
In recent years, some research units and production enterprises at home and abroad carry out toughening modification on PP by the following main methods: metallocene polyolefin modified PP, but the cost is higher; the rubber is blended and modified, and has certain smell; toughening modified PP by inorganic rigid particles: inorganic rigid ultrafine particles such as sub-nanometer or micron calcium carbonate, talcum powder, wollastonite, barium sulfate, kaolin and the like are adopted to modify PP, but the mechanical property is reduced along with the increase of the filling amount. Therefore, a technical means for realizing low temperature resistant toughening modification with excellent toughness of polypropylene is urgently needed to be found.
Disclosure of Invention
The invention provides a plastic sheet for frozen food packaging and a preparation method thereof, aiming at the problem that the existing polypropylene is easy to tear or crack due to low-temperature brittleness and insufficient toughness when being used for food ultra-low temperature frozen packaging.
A plastic sheet for frozen food packaging is prepared by extruding inner layer, middle layer and outer layer materials through a three-layer co-extrusion forming machine set;
the middle layer is prepared by mixing polyurethane-loaded silicon dioxide aerogel and polypropylene powder;
the inner layer and the outer layer are respectively prepared by mixing polypropylene, propylene-ethylene block copolymer and compatilizer.
The polypropylene (PP) extruded sheet for food packaging is a sheet prepared by using polypropylene resin as a main raw material, adding part of auxiliary agents, and carrying out batching and extrusion processes. QS permits the product range to be admitted including: polypropylene (PP) extruded sheets (thickness <1.0mm) for food packaging. Wherein the thicknesses of the inner layer material, the middle layer material and the outer layer material are respectively 0.1-0.5 mm, and the total thickness of the finally prepared plastic sheet for packaging frozen food is less than 1 mm.
Aerogel generally refers to a light nano solid material which is formed by mutually gathering nano-scale ultrafine particles to form a nano porous network structure, and gaseous dispersion media are filled in the pores of the network. Aerogel is a solid but 99% is made up of gas and looks like a cloud in appearance. Aerogels are sometimes referred to as "solid smoke" or "frozen smoke" because of their translucent color and ultra-light weight. SiO 22The aerogel is a light nano porous amorphous solid material with excellent heat-proof and heat-insulating properties, the porosity of the aerogel is as high as 80-99.8%, the typical size of the pores is 1-100 nm, and the specific surface area is 200-1000 m2A density of as low as 3kg/m3The room temperature thermal conductivity can be as low as 0.012W/(m.k). Due to the characteristics, the aerogel material has wide application potential in the aspects of thermal, acoustic, optical, microelectronic and particle detection. Further, the middle layer of the plastic sheet for frozen food packaging is prepared by mixing polyurethane-loaded silicon dioxide aerogel and polypropylene powder according to a mass ratio of 1: 2-5.
According to the invention, high-elasticity polyurethane particles are loaded in micropores of the silicon dioxide aerogel to obtain the silicon dioxide aerogel particles with certain toughness and flexibility. Further, the middle layer of the plastic sheet for frozen food packaging is prepared by mixing the polyurethane-loaded silica aerogel and polypropylene powder according to the mass ratio of 1: 3.
Since the industrial Production of Polypropylene (PP) in the past fifty years, polypropylene (PP) has been widely used due to its excellent mechanical properties, electrical properties, stress cracking resistance, wear resistance, corrosion resistance, solvent resistance and the like, but its use in some fields is limited due to its poor toughness and cold resistance, especially its brittleness at low temperature and the like. The ethylene-propylene block copolymer is a blend of PP, PE, EPR multicomponent components. Further, the plastic sheet for frozen food packaging is prepared by mixing polypropylene, a propylene-ethylene block copolymer and a compatilizer according to a mass ratio of 100: 5-10: 1-2.
Furthermore, the plastic sheet for frozen food packaging is prepared by mixing polypropylene, a propylene-ethylene block copolymer and a compatilizer according to a mass ratio of 100:8: 1.5.
In the invention, the compatilizer can be selected from compatilizers which can promote polypropylene and propylene-ethylene block copolymer to be better combined. Further, the compatilizer is maleic anhydride grafted polypropylene.
Further, the plastic sheet for frozen food packaging is prepared by the following steps of: preparing polyurethane and dimethylformamide into glue solution according to the mass ratio of 8-10: 100, and in order to ensure that the silica aerogel fully adsorbs polyurethane powder, adding the silica aerogel into excessive glue solution for soaking so that the glue solution fully permeates micropores of the silica aerogel; then filtering and conventionally drying to obtain the silica aerogel carrying polyurethane.
Further, if the glue solution is too much, the silica aerogel is saturated in adsorption, and the waste of the glue solution can be caused, and the solid-to-liquid ratio of the silica aerogel to the glue solution is 10-30 g: 100-200 mL, so that the condition that the silica aerogel fully adsorbs polyurethane can be met, the glue solution fully permeates micropores of the silica aerogel, and the excessive waste of the glue solution can not be caused.
The invention also provides a preparation method of the plastic sheet for frozen food packaging, which comprises the following steps:
(1) preparing polyurethane and dimethylformamide into glue solution, and then adding the silica aerogel into the excessive glue solution for soaking to ensure that the glue solution fully permeates micropores of the silica aerogel; then filtering and drying to obtain the silica aerogel loaded with polyurethane;
(2) uniformly mixing the silica aerogel loaded with polyurethane with polypropylene powder to obtain an intermediate layer material; uniformly mixing polypropylene, a propylene-ethylene block copolymer and a compatilizer to obtain an inner layer material and an outer layer material; forming a composite sheet of an inner layer, a middle layer and an outer layer by a three-layer coextrusion forming unit, and further performing press polishing, sizing and coiling by a press roller to obtain the plastic sheet for packaging frozen food.
The invention adopts the three-layer co-extrusion forming machine to prepare the plastic sheet, and the prepared plastic sheet has the characteristics of high barrier property, corrosion resistance, flame retardance, high strength, high physical and mechanical properties, uniform strength, low temperature resistance, attractive appearance and the like. Further, in the preparation method of the plastic sheet for frozen food packaging, the temperature interval of the extruder cylinder of the co-extrusion molding unit in the step (2) is as follows: 170-180 ℃ in a region 1, 200-220 ℃ in a region 2, 200-210 ℃ in a region 3, 180-190 ℃ in a region 4, and 170-180 ℃ in a screen changing runner; the temperature of the film opening is 190-220 ℃.
In order to improve the low-temperature toughness of a PP sheet when the PP sheet is used for freezing packaging, high-elasticity polyurethane is retained in micropores of silicon dioxide aerogel to obtain silicon dioxide aerogel particles with toughness, the substance is built in an intermediate layer of the PP sheet when multi-layer co-extrusion is carried out, the sheet material is endowed with good flexibility, the low-temperature brittleness of the polypropylene sheet material is obviously improved, the polypropylene sheet material has good mechanical properties under the low-temperature freezing condition, and the tearing and the brittle fracture caused by the low-temperature brittleness are avoided.
Drawings
FIG. 1 is a surface condition of a plastic sheet for frozen food packaging prepared in example 1 after the sheet is bent 15 times;
fig. 2 is a surface condition of the plastic sheet for frozen food packaging prepared in comparative example 1 after the sheet is bent 15 times.
Detailed Description
The present invention will be described in further detail with reference to specific embodiments, but it should not be construed that the scope of the present invention is limited to the following examples. Various substitutions and alterations can be made by those skilled in the art and by conventional means without departing from the spirit of the method of the invention described above.
Example 1
A plastic sheet for frozen food packaging is prepared by extruding inner layer, middle layer and outer layer materials through a three-layer co-extrusion forming machine set;
the middle layer is prepared by mixing polyurethane-loaded silicon dioxide aerogel and polypropylene powder according to the mass ratio of 1: 3;
the inner layer and the outer layer are respectively prepared by mixing polypropylene, propylene-ethylene block copolymer and compatilizer according to the mass ratio of 100:8: 1.5;
the compatilizer is maleic anhydride grafted polypropylene;
the preparation method comprises the following steps:
(1) preparing polyurethane and dimethylformamide into glue solution, and then adding the silica aerogel into the excessive glue solution for soaking to ensure that the glue solution fully permeates micropores of the silica aerogel; then filtering and drying to obtain the silica aerogel loaded with polyurethane; the solid-to-liquid ratio of the silica aerogel to the glue solution is 20g:150 mL;
(2) uniformly mixing the silica aerogel loaded with polyurethane with polypropylene powder to obtain an intermediate layer material; uniformly mixing polypropylene, a propylene-ethylene block copolymer and a compatilizer to obtain an inner layer material and an outer layer material; forming a composite sheet of an inner layer, a middle layer and an outer layer by a three-layer coextrusion forming unit, and further performing press polishing, sizing and coiling by a compression roller to obtain a plastic sheet with the total thickness of less than 1mm for packaging frozen food; wherein, the thicknesses of the inner layer, the middle layer and the outer layer are respectively 0.2mm, 0.3mm and 0.5 mm.
The temperature interval of the extruder cylinder of the co-extrusion molding unit is as follows: 175 ℃ in a 1 area, 210 ℃ in a 2 area, 205 ℃ in a 3 area, 185 ℃ in a 4 area and 175 ℃ in a screen changing runner; the temperature of the film opening is 200 ℃.
Example 2
A plastic sheet for frozen food packaging is prepared by extruding inner layer, middle layer and outer layer materials through a three-layer co-extrusion forming machine set;
the middle layer is prepared by mixing polyurethane-loaded silicon dioxide aerogel and polypropylene powder according to the mass ratio of 1: 5;
the inner layer and the outer layer are respectively prepared by mixing polypropylene, propylene-ethylene block copolymer and compatilizer according to the mass ratio of 100:5: 1;
the compatilizer is maleic anhydride grafted polypropylene;
the preparation method comprises the following steps:
(1) preparing polyurethane and dimethylformamide into glue solution, and then adding the silica aerogel into the excessive glue solution for soaking to ensure that the glue solution fully permeates micropores of the silica aerogel; then filtering and drying to obtain the silica aerogel loaded with polyurethane; the solid-to-liquid ratio of the silica aerogel to the glue solution is 30g:200 mL;
(2) uniformly mixing the silica aerogel loaded with polyurethane with polypropylene powder to obtain an intermediate layer material; uniformly mixing polypropylene, a propylene-ethylene block copolymer and a compatilizer to obtain an inner layer material and an outer layer material; forming a composite sheet of an inner layer, a middle layer and an outer layer by a three-layer coextrusion forming unit, and further performing press polishing, sizing and coiling by a compression roller to obtain a plastic sheet with the total thickness of less than 1mm for packaging frozen food; wherein, the thicknesses of the inner layer, the middle layer and the outer layer are respectively 0.2mm, 0.3mm and 0.5 mm.
The temperature interval of the extruder cylinder of the co-extrusion molding unit is as follows: 170 ℃ in a region 1, 200 ℃ in a region 2, 200 ℃ in a region 3, 185 ℃ in a region 4 and 170 ℃ in a screen changing flow channel; the film opening temperature was 220 ℃.
Example 3
A plastic sheet for frozen food packaging is prepared by extruding inner layer, middle layer and outer layer materials through a three-layer co-extrusion forming machine set;
the middle layer is prepared by mixing polyurethane-loaded silicon dioxide aerogel and polypropylene powder according to the mass ratio of 1: 2;
the inner layer and the outer layer are respectively prepared by mixing polypropylene, propylene-ethylene block copolymer and compatilizer according to the mass ratio of 100:6: 2;
the compatilizer is maleic anhydride grafted polypropylene;
the preparation method comprises the following steps:
(1) preparing polyurethane and dimethylformamide into glue solution, and then adding the silica aerogel into the excessive glue solution for soaking to ensure that the glue solution fully permeates micropores of the silica aerogel; then filtering and drying to obtain the silica aerogel loaded with polyurethane; the solid-to-liquid ratio of the silica aerogel to the glue solution is 15g:160 mL;
(2) uniformly mixing the silica aerogel loaded with polyurethane with polypropylene powder to obtain an intermediate layer material; uniformly mixing polypropylene, a propylene-ethylene block copolymer and a compatilizer to obtain an inner layer material and an outer layer material; forming a composite sheet of an inner layer, a middle layer and an outer layer by a three-layer coextrusion forming unit, and further performing press polishing, sizing and coiling by a compression roller to obtain a plastic sheet with the total thickness of less than 1mm for packaging frozen food; wherein, the thicknesses of the inner layer, the middle layer and the outer layer are respectively 0.2mm, 0.3mm and 0.5 mm.
The temperature interval of the extruder cylinder of the co-extrusion molding unit is as follows: the temperature of the area 1 is 180 ℃, the temperature of the area 2 is 220 ℃, the temperature of the area 3 is 210 ℃, the temperature of the area 4 is 190 ℃, and the screen changing flow channel is 180 ℃; the film opening temperature was 210 ℃.
Example 4
A plastic sheet for frozen food packaging is prepared by extruding inner layer, middle layer and outer layer materials through a three-layer co-extrusion forming machine set;
the middle layer is prepared by mixing polyurethane-loaded silicon dioxide aerogel and polypropylene powder according to the mass ratio of 1: 4;
the inner layer and the outer layer are respectively prepared by mixing polypropylene, propylene-ethylene block copolymer and compatilizer according to the mass ratio of 100:9: 2;
the compatilizer is maleic anhydride grafted polypropylene;
the preparation method comprises the following steps:
(1) preparing polyurethane and dimethylformamide into glue solution, and then adding the silica aerogel into the excessive glue solution for soaking to ensure that the glue solution fully permeates micropores of the silica aerogel; then filtering and drying to obtain the silica aerogel loaded with polyurethane; the solid-to-liquid ratio of the silica aerogel to the glue solution is 25g:180 mL;
(2) uniformly mixing the silica aerogel loaded with polyurethane with polypropylene powder to obtain an intermediate layer material; uniformly mixing polypropylene, a propylene-ethylene block copolymer and a compatilizer to obtain an inner layer material and an outer layer material; forming a composite sheet of an inner layer, a middle layer and an outer layer by a three-layer coextrusion forming unit, and further performing press polishing, sizing and coiling by a compression roller to obtain a plastic sheet with the total thickness of less than 1mm for packaging frozen food; wherein, the thicknesses of the inner layer, the middle layer and the outer layer are respectively 0.2mm, 0.3mm and 0.5 mm.
The temperature interval of the extruder cylinder of the co-extrusion molding unit is as follows: the temperature of the 1 area is 172 ℃, the temperature of the 2 area is 220 ℃, the temperature of the 3 area is 206 ℃, the temperature of the 4 area is 188 ℃, and the temperature of the screen changing runner is 175 ℃; the film opening temperature is 195 ℃.
Example 5
A plastic sheet for frozen food packaging is prepared by extruding inner layer, middle layer and outer layer materials through a three-layer co-extrusion forming machine set;
the middle layer is prepared by mixing polyurethane-loaded silicon dioxide aerogel and polypropylene powder according to the mass ratio of 1: 3;
the inner layer and the outer layer are respectively prepared by mixing polypropylene, propylene-ethylene block copolymer and compatilizer according to the mass ratio of 100:5: 1;
the compatilizer is maleic anhydride grafted polypropylene;
the preparation method comprises the following steps:
(1) preparing polyurethane and dimethylformamide into glue solution, and then adding the silica aerogel into the excessive glue solution for soaking to ensure that the glue solution fully permeates micropores of the silica aerogel; then filtering and drying to obtain the silica aerogel loaded with polyurethane; the solid-to-liquid ratio of the silica aerogel to the glue solution is 22g:120 mL;
(2) uniformly mixing the silica aerogel loaded with polyurethane with polypropylene powder to obtain an intermediate layer material; uniformly mixing polypropylene, a propylene-ethylene block copolymer and a compatilizer to obtain an inner layer material and an outer layer material; forming a composite sheet of an inner layer, a middle layer and an outer layer by a three-layer coextrusion forming unit, and further performing press polishing, sizing and coiling by a compression roller to obtain a plastic sheet with the total thickness of less than 1mm for packaging frozen food; wherein, the thicknesses of the inner layer, the middle layer and the outer layer are respectively 0.2mm, 0.3mm and 0.5 mm.
The temperature interval of the extruder cylinder of the co-extrusion molding unit is as follows: 170 ℃ in the area 1, 220 ℃ in the area 2, 200 ℃ in the area 3, 186 ℃ in the area 4 and 174 ℃ in the screen changing flow channel; the film opening temperature was 205 ℃.
Comparative example 1
A plastic sheet for packaging frozen food is prepared by extruding inner and outer layer materials through a two-layer co-extrusion forming machine set;
the inner layer and the outer layer are respectively prepared by mixing polypropylene, propylene-ethylene block copolymer and compatilizer according to the mass ratio of 100:8: 1.5;
the compatilizer is maleic anhydride grafted polypropylene;
the preparation method comprises the following steps:
uniformly mixing polypropylene, a propylene-ethylene block copolymer and a compatilizer to obtain an inner layer material and an outer layer material; forming an inner-outer layer composite sheet by a two-layer coextrusion forming unit, further performing press polishing, sizing and coiling by a press roller to obtain a plastic sheet with the total thickness less than 1mm for packaging frozen food; wherein, the thickness of the inner layer and the outer layer is 0.5mm and 0.5mm respectively.
The temperature interval of the extruder cylinder of the co-extrusion molding unit is as follows: 175 ℃ in a 1 area, 210 ℃ in a 2 area, 205 ℃ in a 3 area, 185 ℃ in a 4 area and 175 ℃ in a screen changing runner; the temperature of the film opening is 200 ℃.
And (3) performance testing:
the sheets obtained in example 1 and comparative example 1 were cut, placed in a refrigerator, frozen at-15 ℃ for 14 hours, and then bent at an angle of 45 °, and the change in the sheet was observed. Example 1 the surface of the sheet was creased after 15 folds, as shown in figure 1; the sheet of comparative example 1 showed significant cracking when bent 3 times, as shown in fig. 2.
Claims (10)
1. A plastic sheet for frozen food packaging is characterized in that the plastic sheet is prepared by extruding an inner layer material, an intermediate layer material and an outer layer material through a three-layer co-extrusion forming machine set;
the middle layer is prepared by mixing polyurethane-loaded silicon dioxide aerogel and polypropylene powder;
the inner layer and the outer layer are respectively prepared by mixing polypropylene, propylene-ethylene block copolymer and compatilizer.
2. The plastic sheet for frozen food packaging as claimed in claim 1, wherein the intermediate layer is prepared by mixing silica aerogel carrying polyurethane and polypropylene powder according to a mass ratio of 1: 2-5.
3. The plastic sheet for frozen food packaging as claimed in claim 1 or 2, wherein the intermediate layer is prepared by mixing silica aerogel carrying polyurethane with polypropylene powder in a mass ratio of 1: 3.
4. The plastic sheet for frozen food packaging as claimed in claim 1, wherein the inner layer and the outer layer are respectively prepared by mixing polypropylene, propylene-ethylene block copolymer and compatilizer according to a mass ratio of 100: 5-10: 1-2.
5. The plastic sheet for frozen food packaging as claimed in claim 1 or 4, wherein the inner layer and the outer layer are respectively prepared by mixing polypropylene, propylene-ethylene block copolymer and compatilizer according to a mass ratio of 100:8: 1.5.
6. Plastic sheet for frozen food packaging according to claim 4 or 5, characterized in that the compatibiliser is maleic anhydride grafted polypropylene.
7. The plastic sheet for frozen food packaging as claimed in claim 1, wherein the silica aerogel carrying polyurethane is prepared by the following method: preparing polyurethane and dimethylformamide into glue solution according to the mass ratio of 8-10: 100, and then adding the silica aerogel into excessive glue solution for soaking to enable the glue solution to fully penetrate through micropores of the silica aerogel; then filtering and drying to obtain the silica aerogel carrying polyurethane.
8. The plastic sheet for frozen food packaging as claimed in claim 7, wherein the solid-to-liquid ratio of the silica aerogel to the glue solution is 10-30 g: 100-200 mL.
9. A method of manufacturing a plastic sheet for frozen food packaging according to any one of claims 1 to 8, characterized in that the specific manufacturing method comprises the steps of:
(1) preparing polyurethane and dimethylformamide into glue solution, and then adding the silica aerogel into the excessive glue solution for soaking to ensure that the glue solution fully permeates micropores of the silica aerogel; then filtering and drying to obtain the silica aerogel loaded with polyurethane;
(2) uniformly mixing the silica aerogel loaded with polyurethane with polypropylene powder to obtain an intermediate layer material; uniformly mixing polypropylene, a propylene-ethylene block copolymer and a compatilizer to obtain an inner layer material and an outer layer material; forming a composite sheet of an inner layer, a middle layer and an outer layer by a three-layer coextrusion forming unit, and further performing press polishing, sizing and coiling by a press roller to obtain the plastic sheet for packaging frozen food.
10. The method for preparing plastic sheet for frozen food packaging as claimed in claim 9, wherein the temperature interval of the extruder barrel of the co-extrusion molding machine set in the step (2) is: 170-180 ℃ in a region 1, 200-220 ℃ in a region 2, 200-210 ℃ in a region 3, 180-190 ℃ in a region 4, and 170-180 ℃ in a screen changing runner; the temperature of the film opening is 190-220 ℃.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112498988A (en) * | 2020-06-04 | 2021-03-16 | 罗瑞尔纳米合成材料(江苏)有限公司 | Functional heat preservation box made of nano synthetic material and capable of being recycled and sterilizing |
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