Sealing film suitable for food packaging and preparation method thereof

Abstract

A sealing film suitable for food packaging is disclosed, which adopts the following solution. The sealing film comprises, in sequence, a PET layer, a VMPET layer and a PE layer from outside to inside, wherein the PE layer comprises 100-110 parts of PE, 15-20 parts of EVA, 15-20 parts of EAA, 55-60 parts of HDPE and 10-15 parts of LLDPE in parts by mass. In this manner, the addition of HDPE and LLDPE into the PE layer is intended to enhance the tensile strength of the sealing film.

Claims

1. A preparation method of a sealing film suitable for food packaging, comprising the following steps: applying an adhesive on both surface of a vacuum metalized polyethylene terephthalate (VMPET) layer, wherein the adhesive is formed by the mixing of corn flour, an anionic surfactant, carbonyl diamide, acrylic acid, polyvinyl alcohol and a photo-curing agent according to the mass ratio of 80:2:3:17:16:5; gluing a polyethylene terephthalate (PET) layer to the lower side of the VMPET layer and a polyethylene (PE) layer to the upper side of the VMPET layer; simultaneously squeezing and clamping the PET layer, the PE layer and the VMPET layer by a pair of nipping rollers to obtain a semi-finished film; drying the semi-finished film; irradiating the semi-finished film by UV; and rolling the semi-finished film to obtain a finished sealing film.

2. The preparation method of the sealing film suitable for food packaging according to claim 1, wherein a preparation method of the PE layer comprises the following steps: adding all raw materials into a mixer for melting and mixing according to the prescribed mass parts; transferring the raw materials to a twin-screw extruder for extrusion and pelletization to obtain PE master batches; and adding the PE master batches into a drawing machine to be drawn into a film.

3. The preparation method of the sealing film suitable for food packaging according to claim 1, wherein intensity of the UV is 30,000 W/(scm.sup.2), and the irradiating time of the UV is 5 seconds.

4. The preparation method of the sealing film suitable for food packaging according to claim 1, wherein the drying step is performed in an oven, hot air in the oven is blown respectively towards the semi-finished film in the direction perpendicular to the surfaces on both sides of the semi-finished film, and hot air blown from the two sides is symmetrical with respect to the semi-finished film.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flow diagram illustrating a preparation process for a sealing film suitable for food packaging.

DESCRIPTION OF THE EMBODIMENTS

(2) The present invention will be further illustrated below in combination with FIG. 1.

Embodiment 1

(3) A preparation method of a sealing film suitable for food packaging is provided, which comprised the following steps:

(4) Step 1: Preparation of a PE layer: 100 Kg of PE, 15 Kg of EVA, 15 Kg of EAA, 55 Kg of HDPE and 10 Kg of LLDPE are added into a mixer. Heating is conducted to make the temperature reach 135° C. for melting and even mixing. Thereafter, the raw materials are transferred to a twin-screw extruder for extrusion and pelletization to obtain PE master batches. Then, the PE master batches are added into a drawing machine to be drawn into a PE layer having a thickness of 2 μm.

(5) Step 2: A VMPET layer having a thickness of 2 μm is enabled to pass between a first pair of nipping rollers. The first pair of nipping rollers grasped the VMPET layer, and adhesives on the first pair of nipping rollers are applied evenly on the upper and lower surfaces of the VMPET layer.

(6) Step 3: A PE layer having a thickness of 4 μm and a PET layer having a thickness of 2 μm are enabled to pass above and below the first pair of nipping rollers to be butted respectively with the upper and lower surfaces of the VMPET layer in an accurate manner. Meanwhile, the two layers are also enabled to pass between a second pair of nipping rollers. At this point, the PE layer, the VMPET layer and the PET layer, which are squeezed by the second pair of nipping rollers, are bonded together tightly to form a semi-finished film.

(7) Step 4: The semi-finished film is delivered through an oven, wherein the temperature of the oven is 80° C., and the delivery time is 1 minute. Moreover, hot air blown from the oven is blown towards the semi-finished film from the upper and lower sides of the semi-finished film and in the direction perpendicular to the semi-finished film. Meanwhile, hot air blown from the upper and lower sides is symmetrical with respect to the semi-finished film.

(8) Step 5: After being delivered through the oven, the semi-finished film is enabled to pass through a UV chamber, wherein the intensity of ultraviolet ray of the UV chamber is 30,000 W/(s.Math.cm.sup.2), and the duration time is 5 seconds. Finally, the semi-finished film is rolled up at an end to obtain a finished sealing film.

(9) Here, the adhesive is formed by the mixing of corn flour, an anionic surfactant, carbonyl diamide (urea), acrylic acid, polyvinyl alcohol and a photo-curing agent according to the mass ratio of 80:2:3:17:16:5. Moreover, the anionic surfactant may be APAM, sodium dodecyl benzene sulfonate, fatty acid sulfoalkyl ester and so on, and the photo-curing agent may be phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide, 2,4-diethylthioxanthone and 1-hydroxy-cyclohexyl-phenyl ketone and so on. The anionic surfactant used herein is sodium dodecyl benzene sulfonate. As such, sodium dodecyl benzene sulfonate may act synergistically with urea, thus possessing good pest-resistant abilities. In this process, when an insect bites the sealing film, urea and sodium dodecyl benzene sulfonate in the adhesive will be absorbed into the body of the insect. At this time, urea will damage chitin of the insect's body walls, while sodium dodecyl benzene sulfonate will dissolve wax layers on the body walls and adhere thereon to form a waterproof and airtight film. As such, spiracles of the insect will be clogged, and it will die from suffocation. In this manner, storage effects of outer packaging on food packaged inside it are further improved.

(10) Additionally, the thickness of the sealing film may be selected based on actual conditions. Normally, the thickness of the PET layer is 1-3 μm, the thickness of the VMPET layer is 2-6 μm, and the thickness of the PE layer is 2-4 μm.

(11) Examples 2-5 and comparative examples 1 and 2 are provided respectively based on the preparation method of Example 1, which are shown in the table below:

(12) TABLE-US-00001 Compar- Compar- Formula ative ative of PE Exam- Exam- Exam- Exam- Exam- Exam- Layer ple 2 ple 3 ple 4 ple 5 ple 1 ple 2 PE/Kg 110 105 100 105 110 105 EVA/Kg 20 17 17 15 20 17 EAA/Kg 20 18 20 15 20 18 HDPE/Kg 60 57 55 57 / / LLDPE/ 15 13 10 15 / / Kg

(13) Meanwhile, the sealing film of examples 1-5 and comparative examples 1 and 2 are tested respectively in accordance with the Detection Standard GB/T10004-2008, wherein the detected sealing films had a same thickness of 8 μm, and the results as shown in the table below are obtained:

(14) TABLE-US-00002 Comparative Comparative Testing Item Example 1 Example 2 Example 3 Example 4 Example 5 Example 1 Example 2 Standard Maximum 60.8 62.4 61.3 61.0 61.8 51.3 50.7 60.1 Force of Stretching/N Stretching 31.5 29.4 30.8 31.2 30.4 43.4 45.2 39.6 Elongation/% Maximum 3.5 3.8 3.6 3.7 3.5 2.1 1.9 3.4 Force of Peeling/N Peeling 2.5 3.0 2.8 2.6 2.7 1.6 1.2 2.2 Strength/MPa

(15) First, the results of mechanical testing for the sealing film of the present invention all comply with relevant criteria of GB/T10004-2008. Secondly, based on the comparison among Examples 2 and 3 as well as Comparative examples 1 and 2, it is quite clear that in the present invention, after the addition of HDPE and LLDPE, the overall tensile strength is obviously improved. As such, when package unsealing is done by pulling, the sealing film may be effectively avoided from being torn up, thereby ensuring the convenience of food taking.

(16) Examples 6-8 is provided on the basis of the preparation method of Example 1, wherein the shell powder as shown in the table below is also added according to Examples 1-3 respectively:

(17) TABLE-US-00003 Component Example 6 Example 7 Example 8 Shell Powder/Kg 2 5 3.5

(18) The shell powder is treated via the following method:

(19) A sodium sulfite buffer solution having a pH value of 8.0 is formulated, and a small amount of triton is used as a surfactant. Then, a combination of alkaline protease, papain and trypsin are used for catalyzation respectively for Examples 6-8, and the shell powder is soaked into the solution. Thereafter, hydrolysis is conducted for 2 hours under the conditions that the temperature of a constant-temperature shaker is controlled to be 50° C., and the rotation speed is controlled to be 300 r/min.

(20) Sealing films of 1 cm.sup.2 are taken respectively from Examples 1-3 and 6-8. A nutrient solution having 10 cfu of Escherichia coli is dripped to each sealing film. Thereafter, the sealing films are placed in an incubator of 35° C. for 24 hours. After that, they are taken out, and bacterial colonies propagating on them are tested to obtain the results as shown in the table below:

(21) TABLE-US-00004 Name of Bacterial Exam- Exam- Exam- Exam- Exam- Exam- Colony ple 1 ple 2 ple 3 ple 3 ple 7 ple 8 Bacterial 506 510 504 1 0 0 Colony of Escherichia Coli/cfu

(22) It can also be seen clearly from the above table that the sealing film of the present invention also has strong bacteriostatic properties. This feature helps prolong the storage time of food.

(23) Additionally, sealing films in Examples 1-8 are placed respectively in the environment of 0° C., −10° C., −20° C., −30° C., −40° C., −50° C., −60° C. and −70° C. for 1 hour. Then, observations are conducted to check whether there are changes in the shapes of various sealing films:

(24) TABLE-US-00005 Temperature Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8  0° C. Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged −10° C. Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged −20° C. Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged −30° C. Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged −40° C. Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged −50° C. Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged −60° C. Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged Unchanged −70° C. Damaged Unchanged Damaged Unchanged Unchanged Damaged Unchanged Damaged

(25) It can be seen clearly from the above table that the sealing film of the present invention still can maintain its original form in the environment of −60° C. This feature may have relatively good protection effects on food stored at low temperature.

(26) The specific embodiments described herein are merely illustrative of the present invention, and not intended to limit the present invention. Upon reading this description, those skilled in the art may make modifications with no creative contributions to the above embodiments according to requirements, but all the modifications that fall within the scope of claims of the present invention shall be protected by the Patent Law.