阅读说明：本技术 可回收再利用的酵母包装复合膜及其制备方法 (Recyclable and reusable yeast packaging composite membrane and preparation method thereof ) 是由 邓锐 熊涛 李知洪 邹家武 王超 于 2019-10-30 设计创作，主要内容包括：本发明公开了一种可回收再利用的酵母包装复合膜及其制备方法,该复合膜由印刷层、热封层二层结构薄膜组成,其中印刷层为真空镀氧化硅的纵向拉伸聚乙烯膜,热封层为多层共挤聚乙烯膜,层与层之间采用无溶剂胶黏剂粘接形成复合膜。印刷层是采用三层共挤吹塑成型和纵向拉伸上吹工艺制备得到纵向拉伸聚乙烯膜,采用真空镀膜技术在纵向拉伸聚乙烯膜的镀层表面蒸镀氧化硅,将印刷层与热封层采用无溶剂胶黏剂进行粘贴并熟化,得到可回收再利用的酵母包装复合膜。该复合膜能满足阻隔性能要求,采用可回收再利用的材质制备,符合环保要求。(The invention discloses a recyclable and reusable yeast packaging composite film and a preparation method thereof. The printing layer is a longitudinally stretched polyethylene film prepared by adopting a three-layer co-extrusion blow molding and longitudinally stretching up-blowing process, silicon oxide is evaporated on the surface of a coating of the longitudinally stretched polyethylene film by adopting a vacuum coating technology, and the printing layer and the heat sealing layer are adhered by adopting a solvent-free adhesive and cured to obtain the recyclable and reusable yeast packaging composite film. The composite film can meet the requirement of barrier property, is prepared by adopting recyclable materials, and meets the requirement of environmental protection.)

1. Recoverable yeast packaging composite membrane of recycling which characterized in that: the composite film consists of a printing layer and a heat sealing layer, wherein the printing layer is a longitudinal stretching polyethylene film plated with silicon oxide in vacuum, the heat sealing layer is a multilayer co-extrusion polyethylene film, and solvent-free adhesives are adopted to bond the layers to form the composite film.

2. The composite film of claim 1, wherein: the thickness of the printing layer is 20-50 microns.

3. The composite film of claim 1, wherein: the thickness of the heat sealing layer is 40-100 microns.

4. A method of preparing a composite membrane according to any one of claims 1 to 3, comprising the steps of:

1) the longitudinally stretched polyethylene film is prepared by adopting a three-layer co-extrusion blow molding and longitudinally stretching up-blowing process, wherein the three-layer co-extrusion comprises a corona layer, a middle layer and a coating layer, the thickness ratio of the three-layer co-extrusion layers is =1:2:1, and the blow-up ratio is =3: 1; when longitudinally stretching, the stretching ratio is 3.5-4.2;

2) evaporating 20-40 nm of silicon oxide on the surface of a coating of the longitudinally stretched polyethylene film by adopting a vacuum coating technology, and finishing printing on the surface of a corona layer to obtain the longitudinally stretched polyethylene film plated with the silicon oxide in vacuum as a printing layer;

3) and sticking and curing the printing layer and the heat-sealing layer by adopting a solvent-free adhesive to obtain the recyclable and reusable yeast packaging composite film.

5. The method of claim 4, wherein: in the step 1), the corona layer of the three-layer co-extrusion adopts a blend of high-density polyethylene with the mass content of 80% and low-density polyethylene with the mass content of 20%, wherein the high-density polyethylene is as follows: 0.93-0.94g/cm ³The melt index is: 1-1.5g/10min, the low density polyethylene is: 0.918-0.927g/cm ³The melt index is: 1.5-2.8g/10 min.

6. The method of claim 4, wherein: in the step 1), the middle layer of the three-layer co-extrusion is high-density polyethylene, and the density is as follows: 0.94-0.96 g/cm ³The melt index is: 1-1.5g/10 min.

7. The method of claim 4, wherein: in the step 1), the three-layer co-extruded coating is a blend of 80% by mass of high-density polyethylene and 20% by mass of metallocene polyethylene, wherein the density of the high-density polyethylene is as follows: 0.93-0.95g/cm ³The melt index is: 0.5-1g/10 min.

8. The method according to any one of claims 4-7, wherein: adopting a six-roller differential longitudinal stretching process, wherein the temperature of a preheating roller 1 is 40-45 ℃, and the temperature of a preheating roller 2 is as follows: 50-65 ℃, and the temperature of the stretching roller 1 is set as follows: 80-90 ℃, the temperature of the stretching roller 2 is set as follows: 100 degrees; the annealing roller 1 temperature was set to: 60 ℃, the annealing roller 2 temperature was set to: the stretching speed is 30-40m/min at 40-50 ℃.

9. The method of claim 4, wherein: the corona value of the corona surface after the silicon oxide is plated in the step 2) is more than or equal to 42 dyne.

10. The method of claim 4, wherein: during the bonding in the step 3), polyurethane two-component solvent-free adhesive is adopted, the heat sealing layer and/or the printing layer are/is taken as a base material for coating and gluing, and the total gluing amount is 1.6g/m ²And curing at 40 ℃ for 24 hours.

Technical Field

The invention relates to the field of packaging, in particular to a recyclable and reusable yeast packaging composite film and a preparation method thereof.

Background

Yeast is a unicellular fungus, belongs to facultative anaerobes, and is widely used in the food industry and the fermentation industry as a microbial thallus which is first industrialized by human beings. The active dry yeast is an organism in a hibernation state, and can wake up after meeting water and an environment with sugar, reproduce, grow and lose activity. In recent times, Instant active dry yeast (also called high-activity dry yeast) is prepared by adopting genetic engineering and modern drying technology, compared with the active dry yeast, the moisture content is lower, only 4% -6%, most of the Instant active dry yeast is faint yellow round or rod-shaped particles, the particle size is generally 0.5 mm, (the fermentation speed is high, the Instant active dry yeast can be directly used without pre-hydration in use, at present, domestic and foreign yeast companies mainly adopt aluminum-plastic composite films for vacuum packaging to form specifications markets such as 500 g/bag and 100 g/bag, the shelf life (quality guarantee period) is 1-2 years, the aluminum-plastic composite film packaging mainly has the function of barrier property, namely air and oxygen are isolated, the yeast is in a 'hibernation state', polyethylene is a product obtained by performing polyaddition chemical reaction on petroleum cracking product ethylene, and has excellent chemical stability, biocompatibility, heat sealing properties, and therefore, polyethylene films are often used as inner materials of aluminum-plastic composite films for direct contact with yeast. Meanwhile, the molding processing mode is wide, and the plastic recycling market is the fastest growing part.

World famous yeast companies such as French-style yeast (Lesafre), English-Marri (AB Mauri), Chinese Angel yeast (Angel), mainly adopt polyethylene terephthalate/aluminum foil/polyethylene terephthalate/polyethylene (PET/AL/PET/PE) four-layer structure composite membrane for yeast commodity packaging, wherein, the printing layer adopts 12 micron thickness polyethylene terephthalate film, the barrier layer adopts 7 micron or 9 micron thickness aluminum foil, the heat-seal layer adopts polyethylene film, adopt polyurethane adhesive to laminate between the layer, form the plastic-aluminum composite membrane.

The Chinese patent 'high-barrier composite packaging film' (patent number: 201020534921.3) discloses a substrate layer, a printing layer, a barrier layer, a protective layer and a heat-sealing layer, wherein the substrate layer is sequentially covered with the printing layer, the barrier layer, the protective layer and the heat-sealing layer, and the printing layer is bonded with the barrier layer, the barrier layer is bonded with the protective layer and the heat-sealing layer through bonding layers. The Chinese patent 'a high-activity dry yeast packaging composite film' (patent number: 201120150508.1) discloses a four-layer high-activity dry yeast packaging composite film, wherein the outer layer is a printing layer, the second outer layer is an aluminum foil barrier layer, the third layer is a polyester film or a nylon film, the innermost layer is a modified polyolefin heat-sealing layer, and the layers are bonded through an adhesive.

The aluminum-plastic composite film has certain disadvantages: 1, the production process mainly adopts gravure inner printing and dry composite technology, and the composite film inevitably has a certain amount of solvent residue (the national standard requirement is less than or equal to 5 mg/m) ²) (ii) a 2, after the commodity is used, the packaging film forms aluminum-containing waste which cannot be recycled, so that 'white pollution' which is harmful to the environment is formed; and 3, the packaging material is derived from petrochemical polymers, cannot be degraded in a natural environment, and causes environmental burden.

Disclosure of Invention

The invention provides a recyclable yeast packaging composite film and a preparation method thereof, which can meet the requirement of barrier property, are prepared from recyclable materials and meet the requirement of environmental protection.

The technical scheme adopted by the invention is that the recyclable yeast packaging composite film is composed of a printing layer and a heat sealing layer, wherein the printing layer is a longitudinal stretching polyethylene film plated with silicon oxide in vacuum, the heat sealing layer is a multi-layer co-extrusion polyethylene film, and the layers are bonded by a solvent-free adhesive to form the composite film.

Further, the thickness of the printing layer is 20-50 microns.

Further, the thickness of the heat sealing layer is 40-100 microns.

The invention also relates to a method for preparing the composite membrane, comprising the following steps:

1) the longitudinal stretching polyethylene film is prepared by adopting a three-layer co-extrusion blow molding and longitudinal stretching up-blowing process, wherein the three-layer co-extrusion comprises a corona layer, a middle layer and a coating layer, the thickness ratio of the three-layer co-extrusion layers is 1:2:1, and the blow-up ratio is 3: 1; when longitudinally stretching, the stretching ratio is 3.5-4.2;

2) evaporating 20-40 nm of silicon oxide on the surface of a coating of the longitudinally stretched polyethylene film by adopting a vacuum coating technology, and finishing printing on the surface of a corona layer to obtain the longitudinally stretched polyethylene film plated with the silicon oxide in vacuum as a printing layer;

3) and sticking and curing the printing layer and the heat-sealing layer by adopting a solvent-free adhesive to obtain the recyclable and reusable yeast packaging composite film.

Further, in the step 1), the corona layer of the three-layer co-extrusion adopts a blend of high-density polyethylene and low-density polyethylene with the mass content of 80%, wherein the high-density polyethylene is as follows: 0.93-0.94g/cm ³The melt index is: 1-1.5g/10min, the low density polyethylene is: 0.918-0.927g/cm ³The melt index is: 1.5-2.8g/10 min.

Further, in the step 1), the middle layer of the three-layer co-extrusion is made of high-density polyethylene, and the density is as follows: 0.94-0.96 g/cm ³The melt index is: 1-1.5g/10 min.

Further, in the step 1), the three-layer co-extruded coating is a blend of 80% by mass of high-density polyethylene and 20% by mass of metallocene polyethylene, wherein the density of the high-density polyethylene is as follows: 0.93-0.95g/cm ³The melt index is: 0.5-1g/10 min. When the corona layer, the middle layer and the coating layer are co-extruded, the density of the middle layer is greater than the densities of the corona layer and the coating layer on two sides, so that crystallization is facilitated.

Further, a six-roller differential longitudinal stretching process is adopted, the temperature of the preheating roller 1 is 40-45 ℃, and the temperature of the preheating roller 2 is as follows: 50-65 ℃, and the temperature of the stretching roller 1 is set as follows: 80-90 ℃, the temperature of the stretching roller 2 is set as follows: 100 degrees; the annealing roller 1 temperature was set to: 60 ℃, the annealing roller 2 temperature was set to: the stretching speed is 30-40m/min at 40-50 ℃.

Further, the corona value of the corona surface after the step 2) of silicon oxide plating is more than or equal to 42 dynes.

Further, during the bonding in the step 3), polyurethane two-component solvent-free adhesive is adopted, the heat sealing layer and/or the printing layer are/is taken as a base material for coating and gluing, and the total gluing amount is 1.6g/m ²When cured, isAging at 40 deg.C for 24 h.

Preferably, the coating surface is treated by a plasma process, and then silicon oxide with the thickness of 20-40 nanometers is evaporated on the surface of the polyethylene by a vacuum coating technology. And (3) removing impurities on a film interface layer by adopting a plasma process, and improving the polarity of the material, thereby enhancing the surface adhesion of silicon oxide and polyethylene.

Polyethylene is nontoxic and harmless, is a plastic film material with the best biocompatibility at present, has good heat sealing property, is very suitable for the requirement of production line type automatic packaging of yeast products, belongs to thermoplastic plastics, has wide molding processing modes and is a part of the fastest growth of plastic recycling markets.

However, there are two major problems if polyethylene film materials are used for packaging:

(1) the material is flexible and easy to stretch, and is not easy to print overprint;

(2) the barrier properties are poor.

In order to be able to solve the above problems, the present invention is based on a PE film formed by blow moulding and then by an in-line longitudinal stretching process. The specific process is blow molding and longitudinal stretching, the film is formed by the blowing and air cooling technology, and the film is stretched by MDO multi-roller at 4-6 multiplying power, and the molecular chain of the material is longitudinally crystallized and oriented due to the fact that only longitudinal stretching is carried out, so that the printing performance is certain.

The silicon oxide plating process is to evaporate silicon oxide on a plastic film in a vacuum sputtering mode, so that the plastic film has high oxygen and water resistance and is mainly used for BOPET and BOPP base materials. Because PE belongs to flexible materials and a compact silicon oxide ceramic layer is difficult to form on the surface of the PE, the invention innovatively adopts a blow molding on-line longitudinal stretching process, and the molecular chain of the material is subjected to longitudinal crystallization orientation, so that the PE film has good flatness and tensile strength in the longitudinal direction, and then the interface polarity of the material is enhanced by adopting a plasma treatment process so as to enhance the adhesion fastness of the surface of the PE film and the silicon oxide material.

The invention can greatly improve the core mechanical properties of the film, such as tensile strength and tensile modulus by 2-3 through the treatment of longitudinal stretching (MDO) up-blowing processAnd (4) doubling. In addition, the barrier performance of the polyethylene film can be greatly improved by evaporating the silicon oxide layer on the polyethylene film, wherein the oxygen transmission capacity (OTR) is less than or equal to 3cm ³/(m ²24h 0.1MPa), Water Vapor Transmission (WVT) of not more than 3g/(m ²·24h)。

According to the invention, in the yeast product packaging process, a two-layer structure design is adopted, the film processing and forming technology is combined with the vacuum silicon oxide plating technology, the printing layer adopts a longitudinal stretching polyethylene film plated with vacuum silicon oxide, and the heat sealing layer adopts multilayer co-extrusion polyethylene, so that the packaging characteristic of the material with a high barrier function is met, and the polyethylene substrate is favorable for recycling and meeting the environmental protection requirement. Furthermore, in order to facilitate recycling, the printing pattern adopts a flexographic printing process, the printing layer and the heat sealing layer are bonded by a solvent-free adhesive composite process, and in addition, in the melting, granulating and recycling process of the packaging composite film, silicon oxide can become inorganic particles to be dispersed in polyethylene, and the packaging composite film can also play an inorganic reinforcing role on a polymer matrix without generating a secondary toxic effect.

Detailed Description

The invention is further illustrated by the following examples, but the scope of the invention as claimed is not limited to the scope of the examples.