Shrinkable film capable of being overlapped and heat sealed, preparation method therefor, and packaging bag prepared using same

Abstract

A shrinkable film capable of being overlapped and heat sealed, a preparation method for the film, and a packaging bag prepared using same, including outer surface layers and a heat sealing layer. Each outer surface layer includes a low-molecular weight compound and is subjected to electron cross-linking treatment, and the low-molecular weight compound is selected from paraffin, oleamide, stearic acid, and one or more of their derivatives. The low-molecular weight compound in each outer surface layer can, during overlapping and heat sealing, be migrated in a polymer under the action of being heated to influence movement of polymer molecular chains, and can be migrated to two molten interfaces to hinder mutual penetration of the polymer molecular chains. Further, by performing electronic cross-linking treatment on the outer surface layers, the outer surface layers form a polymer molecular chain cross-linking structure, and the movement of the polymer molecular chains is reduced.

Claims

1. An overlapping heat sealable shrink film, including an outer layer and a heat sealing layer, wherein the outer layer contains Polyolefin, Ethylene copolymer, low molecular weight compounds and is after electronically crosslinked treatment, the material of the heat sealing layer is one or more of Polyolefin, Ethylene copolymer and Surlyn, the low molecular weight compounds are selected from one or more of Paraffin, Oleamide, Stearic acid and their derivatives, and the Ethylene copolymer is selected from Ethylene-Vinyl acetate copolymer, Ethylene-Methyl acrylate copolymer, Ethylene-Acrylic acid copolymer and Ethylene-Maleic anhydride copolymer; wherein the overlapping heat sealable shrink film contains the following layers from outside to inside: outer layer, containing 60 wt % to 95 wt % Polyolefin, 3 wt % to 10 wt % Ethylene copolymer and 2 wt % to 30 wt % low molecular weight compounds; intermediate layer, wherein the material is one or more of Vinylidene chloride copolymer, Ethylene vinyl alcohol copolymer, Polyolefin, Ethylene copolymer and Surlyn; and wherein sealing layer contains 50 wt % to 100 wt % Polyethylene and 0 wt % to 50 wt % Ethylene-vinyl acetate copolymer.

2. The overlapping heat sealable shrink film as stated in claim 1, wherein the content of the low molecular weight compounds in the outer layer is 0.5˜50 wt %.

3. The overlapping heat sealable shrink film as stated in claim 1, wherein the outer layer and the intermediate layer, the intermediate layer and the heat sealing layer are respectively bonded by one or two adhesive layers; and wherein material of the adhesive layer is one or more of Polyolefin, Ethylene copolymer and Surlyn.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings illustrate one or more embodiments of the present invention and, together with the written description, serve to explain the principles of the invention. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like elements of an embodiment.

(2) FIG. 1 is a schematic view showing the structure of an overlapping heat sealable shrink film in Examples 2-7 of this invention.

SPECIFIC METHODS FOR CARRYING OUT THE INVENTION

(3) Hereinafter the present invention will be explained in greater detail using Examples and Comparative Examples. However, the present invention is not limited by these specific examples, and any technical person with knowledge of this field may achieve similar results by making some changes to the present invention, which are also included in the present invention.

EXAMPLES 1-7 AND COMPARATIVE EXAMPLES 1-8

(4) TABLE-US-00001 TABLE 1 Raw Material Melting Raw Material temperature LLDPE1 100° C. LLDPE2 104° C. EVA1 (10% VA) 98° C., 100° C. EVA2 (18% VA) 89° C., 86° C. LLDPE 123° C. PP (block copolymerization) 162° C. Surlyn  98° C. PA6,66copo1ymer 190° C. PA6I/6T — Tie (Adhesive resin) 119° C. stearic acid 144° C.

(5) TABLE-US-00002 TABLE 2 Raw Material and Mass Percentage of Each Layer in Examples 1-7 and Comparative Examples 1-8 Adhesive Adhesive Interlayer Adhesive Adhesive Inner layer E layerD2 layerD1 C layerB2 layerB1 Outer layer A Example 55% LLDPE — — — — —  90% LLDPE 1 45% EVA2   5% EVA2   5% stearic acid Example 55% LLDPE 20% LLDPE EVA2 PVdC EVA2 20% LLDPE  90% LLDPE1 2 45% EVA2 80% EVA2 80% EVA2   5% EVA2   5% stearic acid Example 55% LLDPE 20% LLDPE EVA2 PVdC EVA2 20% LLDPE  90% LLDPE 3 45% EVA2 80% EVA2 80% EVA2   5% EVA2   5% stearic acid Example 55% LLDPE 20% LLDPE EVA2 PVdC EVA2 20% LLDPE  90% LLDPE 4 45% EVA2 80% EVA2 80% EVA2 9.5% EVA2 0.5% oleamide Example 55% LLDPE 20% LLDPE EVA2 PVdC EVA2 20% LLDPE  75% LLDPE 5 45% EVA2 80% EVA2 80% EVA2   5% EVA2  20% oleamide Example 55% LLDPE 20% LLDPE EVA2 PVdC EVA2 20% LLDPE  65% LLDPE 6 45% EVA2 80% EVA2 80% EVA2   5% EVA2  30% butyl stearate Example 55% LLDPE 20% LLDPE EVA2 PVdC EVA2 20% LLDPE  45% LLDPE 7 45% EVA2 80% EVA2 80% EVA2   5% EVA2  50% butyl stearate Comp. 55% LLDPE 20% LLDPE EVA2 PVdC EVA2 20% LLDPE  90% LLDPE Ex. 1 45% EVA2 80% EVA2 80% EVA2  10% EVA2 Comp. 55% LLDPE 20% LLDPE EVA2 PVdC EVA2 20% LLDPE  90% LLDPE1 Ex. 2 45% EVA2 80% EVA2 80% EVA2  10% EVA2 Comp. 75% POP1 30% Surlyn EVA2 PVdC EVA2 30% Surlyn  68% PP Ex. 3 25% POP2 70% EVA2 70% EVA2  32% POP3 Comp. 65% LLDPE 50% LLDPE EVA1 PVdC EVA1 30% LLDPE  50% LLDPE Ex. 4 35% EVA1 50% EVA1 70% EVA1  50% EVA1 Comp. 50% POP2 20% POP2 EVA2 PVdC EVA2 Tie  80% PA6,66 Ex. 5 50% EVA1 60% EVA2  20% PA6I/6T 20% Surlyn Comp. 50% POP2 20% POP2 EVA2 PVdC EVA2 20% LLDPE PP Ex. 6 50% EVA1 60% EVA2 60% EVA2 20% Surlyn 20% Surlyn Comp. 50% POP2 20% POP2 EVA2 PVdC EVA2 20% LLDPE  68% PP Ex. 7 50% EVA1 60% EVA2 60% EVA2  32% LLDPE2 20% Surlyn 20% Surlyn Comp. 55% LLDPE 20% LLDPE EVA2 PVdC EVA2 20% LLDPE  90% LLDPE Ex. 8 45% EVA2 80% EVA2 80% EVA2   5% EVA2   5% stearic acid

(6) In Examples 1-7 and Comparative Examples 1-7, shrink films are prepared by the following three steps:

(7) S 1: Put the raw materials of each layer shown in Table 2 into a co-extrusion extruder with a multi-layer co-extrusion die head to produce a film tube and then cool the film tube;

(8) S2: Heat the co-extrusion tube and blow-mold to form a film bubble and obtain a bi-directional structure. After cooling and finalizing, the multi-layer co-extrusion shrink film is made;

(9) S3: Electron beam irradiation the shrink film to form a polymer molecular chain crosslinked structure on the outer layer. The voltage range is 125 Kev to 500 Kev and the electron radiation dosage is 3 Mrad to 20 Mrad.

(10) Among them, the film of Example 1 has a two-layer structure and the films of Examples 2-6 and Comparative Examples 1-7 have a seven-layer structure. The outer layers in Comparative Examples 1-7 do not have low molecular weight compounds such as stearic acid.

(11) The raw materials of Comparative Example 8 are the same as Example 3, but the shrink film is prepared according to Step 1 to Step 2, without the electron beam irradiation in Step 3.

(12) Performance test and overlapping heat sealing test of shrink film prepared in Examples 1-7 and Comparative Examples 1-8.

(13) The contents of overlapping heat sealing test are as follows: Overlap two or three bags together for vacuum sealing and repeat the trial for 10 times; Adhesion refers to the times that the outer surfaces of two bags are fused together and unpeelable, the more the times, the worse the overlapping heat sealing effect will be; Tight sealing refers to the times that the outer surfaces of two bags stick together, but separate after the thermal shrinking, the less the times, the better the overlapping heat sealing effect will be.

(14) The performance test and the overlapping heat sealing test results are shown in Table 3.

(15) TABLE-US-00003 TABLE 3 The Performance Results of Examples 1-7 and Comparative Examples 1-8 Exterior/ interior Overlapped Overlapped difference 80° C. heat sealing heat sealing in resin Thermal Degree Stretching property property melting shrinkage of power (two bags) (three bags) temperature rate % haze MPa fusion/ fusion/ ° C. Layer ratio % MD/TD % MD/TD adherence* adherence* Example 34-37 40/60 32/35 16.2 47/49 0/0 0/0 1 Example 18-39 12/15/10/6/12/20/25 41/51 17.11 55/58 0/0 0/0 2 Example 0 12/15/10/6/12/20/25 38/46 15.53 50/52 0/0 0/0 3 Example 0 12/15/10/6/12/20/25 38/45 15.83 51/52 0/0 0/1 4 Example 0 12/15/10/6/12/20/25 39/46 16.12 50/52 0/0 0/0 5 Example 0 12/15/10/6/12/20/25 37/43 15.64 49/50 0/0 0/0 6 Example 0 12/15/10/6/12/20/25 36/41 16.42 48/49 0/0 0/0 7 Comp. 0 12/15/10/6/12/20/25 39/46 15.54 48/49 10/0  10/0  Ex. 1 Comp. −19 12/15/10/6/12/20/25 40/46 16.44 49/51 10/0  10/0  Ex. 2 Comp. 94 12/17/9/6/12/23/21 45/60 21 48/49 0/1  0/10 Ex. 3 Comp. 0 12/15/10/6/10/20/27 30/40 15 40/50 10/0  10/0  Ex. 4 Comp. 122 12/10/15/6/15/20/22 35/46 10 51/58  0/10  0/10 Ex. 5 Comp. 62-64 12/19/12/6/11/20/20 38/47 15.14 50/55 0/0 0/2 Ex. 6 Comp. 62-64 12/19/12/6/11/20/20 41/50 16.18 49/53 0/0 0/3 Ex. 7 Comp. 0 12/15/10/6/12/20/25 38/46 16.48 40/45 10/0  10/0  Ex. 8

(16) From the results in Table 3, the melting temperature of the inner and outer layers of Comparative Examples 1, 2, 4 and 8 are similar. However, under the condition of without low-molecular weight compounds (Comparative Examples 1 and 2) or without electron beam irradiation the outer layer (Comparative Example 8), the overlapping heat sealing effect is poor and the bags adhered seriously. The melting temperature difference between the inner and outer layers of Comparative Example 3 and Comparative Example 5 is large, even it is better in anti-adhesion performance, but poor in tight sealing performance. Comparative Examples 6 and 7 also have the problem of poor tight sealing performance when the bags are overlapped and heat sealed together. It can be seen that the Comparative Examples 1-8 cannot meet the requirements of better sealing and anti-adhesion performance which cannot be applied to the overlapping heat sealing of multiple bags. Low-molecular weight compounds are employed in the outer layers of films in Examples 1-7 and the outer layers are treated by electron beam irradiation, so they are not easy to adhere when heated. Although the melting temperature difference between the inner and outer layers is 0° C. to 64° C., there is still a better sealing performance At the same time, it can effectively prevent the adhesion between the two bags and the bags can still be easily separated after thermal shrinking, so Examples 1-7 are applicable to the overlapping heat sealing of multiple bags.

(17) Moreover, there is no obvious difference in the term of shrinking performance between Examples 1-7 and Comparative Examples 1-8, including machining direction (MD) and transverse direction (TD), degree of haze (transparency) and stretching power.

(18) The preferred examples of the invention have been explained in detail above. However, the present invention is not limited by these specific examples, and under the precondition of subjecting the spirit of the invention, any technical person with knowledge of this field may achieve similar results by making some changes to the present invention, which are also included in the present invention.

(19) The foregoing description of the exemplary embodiments of the present invention has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching.

(20) The embodiments were chosen and described in order to explain the principles of the invention and their practical application so as to activate others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.