Fluid substance packaging sheet and preparation method thereof

Abstract

The invention provides a fluid substance packaging sheet and a preparation method thereof, the fluid substance packaging sheet is formed by sequentially laminating a surface layer, an easy-to-tear light blocking layer and an inner layer, the surface layer adopts a CPP or DPET film prepared by a tape casting process, and has high elongation at break and low haze; the easy-to-tear light-blocking layer is made of a PP / PE and COC blended material, contains more than 10% of a light-blocking agent and more than 20% of COC, and has easy-to-tear property and light-blocking property; the inner layer is of a co-extrusion blown film structure with more than seven layers, comprises an EVOH barrier layer and a polyolefin-COC blending layer, and provides high oxygen barrier property. All the layers are bonded through a dry or solvent-free composite process, and the composite adhesive contains polyurethane. The preparation method comprises a layered preparation process and a compounding process, and the inner layer is processed by seven-layer co-extrusion film blowing. The material is suitable for blister / blow molding packaging of fluid food, medicines or cosmetics, and has the advantages of high barrier property, easiness in opening, forming stability and printing adaptability.

Description

Technical Field

[0001] The present invention relates to the technical field of composite sheets, in particular to packaging sheets, especially composite sheets used for packaging fluid substances and a method for preparing the sheets. Background Art

[0002] Fluid foods include, but are not limited to, pastes, cheeses, beverages, gels, etc., which are squeezed out of the outer packaging to allow the fluid food to flow out from the opening of the packaging. The packaging of such foods requires good sealing and barrier properties and is easy to open for consumption.

[0003] Most current sheets for fluid foods utilize single-layer or simple multilayer structures, such as PE / PP, which fail to simultaneously meet the requirements for high barrier properties, easy opening, and molding stability. As shown in patent application CN117944350A, while the inclusion of an EVOH barrier layer improves oxygen barrier properties, the material's high tear strength makes opening difficult in practice. Furthermore, its light barrier properties are insufficient, and ultraviolet radiation can damage nutrients in food. Furthermore, the lack of interlayer bonding strength in the multilayer composite structure can easily lead to delamination during the molding process.

[0004] Based on the above, it is necessary to develop a fluid material packaging sheet that has barrier properties, is easy to open, and can be well formed and processed. Summary of the Invention

[0005] The object of the present invention is to overcome the deficiencies of the prior art and provide a fluid material packaging sheet having good light blocking effect, molding stability and barrier properties.

[0006] To achieve the above objectives, the present invention provides the following technical solutions: A fluid material packaging sheet comprises a surface layer, an easy-to-tear light-blocking layer and an inner layer which are sequentially laminated with glue.

[0007] The surface layer is a film prepared by a casting process, selected from: The CPP produced by the casting process after blending HOPP and COPP has a thickness of 20-70μm, an elongation at break ≥600%, a haze ≤8%, and a thickness uniformity deviation ≤3%; Alternatively, the DPET produced by the casting process has a thickness of 10-40 μm, an elongation at break ≥ 300%, a haze ≤ 2%, and a thickness uniformity deviation ≤ 2%.

[0008] As a preferred embodiment, the thickness of CPP is 30-60 μm, and the thickness of DPET is 12-25 μm.

[0009] HOPP refers to highly oriented polypropylene (HOPP), which is produced through a biaxial stretching process and has highly oriented molecular chains. COPP refers to cast polypropylene (COPP), which is produced through a casting process and has a lower degree of molecular chain orientation due to longitudinal stretching. The blend ratio of the two can range from 3:7 to 7:3.

[0010] DPET refers to amorphous polyethylene terephthalate, which has improved flexibility and transparency compared to conventional polyethylene terephthalate due to suppressed crystallinity.

[0011] The surface layer can be prepared by melt blending HOPP and COPP in proportion and extruding them through a T-die to a cooling roller to form a CPP film with a thickness of 20-70 μm, or by a casting process to produce a DPET film with a thickness of 12-25 μm.

[0012] The tearable light-blocking layer is a blend of polyolefin (PE and / or PP) and COC, and a light-blocking agent is added during its preparation process. The amount of light-blocking agent added is ≥10% of the total mass of the tearable light-blocking layer, and the amount of COC added is ≥20% of the total mass of the tearable light-blocking layer. The transmittance is ≤5%, and the thickness of the tearable light-blocking layer is 60-200μm.

[0013] In the present invention, the COC content is ≥20% in order to improve the rigidity of the light-blocking and tearable layer, but its content should be controlled not to exceed 30% to avoid brittle cracking.

[0014] As a preferred embodiment, the light blocker includes but is not limited to: at least one of titanium dioxide, zinc oxide, barium sulfate, carbon black, benzotriazole light stabilizers, etc., or a combination thereof. Considering that this packaging is suitable for food, the use of lead and cadmium-based light blockers that do not meet food contact standards, such as lead dioxide, lead trioxide, lead sulfate, etc., should also be avoided in the application of food packaging.

[0015] As a preferred embodiment, the trouser-type tearing force of the tearable light-blocking layer is ≤1N.

[0016] As a preferred embodiment, the thickness of the tearable light-blocking layer is 100-160 μm.

[0017] The tearable light-blocking layer can be prepared by melt-blending PP and / or PE with COC (cyclic olefin copolymer) and light-blocking agent through a twin-screw extruder, and forming a film using a multi-layer co-extrusion or blown film process.

[0018] As a preferred embodiment, the cycloolefin copolymer includes ethylene-norbornene copolymer, propylene-cyclopentene copolymer, styrene-cyclohexene copolymer and the like.

[0019] The inner layer is a co-extruded blown film of no less than 7 layers, and its composition structure is polyolefin, polyolefin-COC blend, adhesive layer, polyvinyl alcohol (EVOH), adhesive layer, polyolefin-COC blend, and polyolefin.

[0020] The polyolefin of the inner layer can be at least one of polyethylene, polypropylene, or a copolymer or homopolymer thereof. The COC in the inner layer accounts for ≥15% of the total mass of the inner layer, and the EVOH thickness is ≥5 μm. The total thickness of the inner layer is 40-100 μm.

[0021] As a preferred embodiment, the trouser-type tearing force of the inner layer is ≤1N.

[0022] As a preferred embodiment, the thickness of the inner layer is 50-70 μm.

[0023] The material of the adhesive layer can be selected from maleic anhydride grafted polyolefin (MAH-g-PP / PE), ethylene-acrylate-maleic anhydride terpolymer, and the like.

[0024] As a preferred embodiment, the maleic anhydride grafting rate is ≥0.8 wt %, and the thickness of the adhesive layer is 3-8 μm.

[0025] When polypropylene is selected as the inner layer polyolefin, it is preferably a blend of COPP and HOPP, and the density of the blended polypropylene is 0.88-0.92g / m 3 .

[0026] When polyethylene is used as the inner polyolefin, it is blended with ionomer and has a density of 0.86-0.91g / m 3 .

[0027] Ionomers are formed by crosslinking ethylene-acrylic acid copolymers with metal ions. The inner polyethylene layer is produced by melt blending PE and ionomers, with the weight ratio of PE to ionomer ranging from 70:30 to 90:10. The contributions of ionomers include, but are not limited to, lowering heat-sealing temperatures and providing controlled tear paths through ionic crosslinking points.

[0028] The inner layer is prepared by a 7-layer co-extrusion film blowing machine, which extrudes each layer from the outside to the inside. The blow-up ratio is controlled at 2.5-3.5, and the bubble cooling wind speed is uniform to avoid excessive thickness deviation.

[0029] Specifically, when the inner layer is a PP substrate, the blowing ratio is preferably 3.0-3.5; when it is a PE substrate, the blowing ratio is preferably 2.5-3.0. The blowing ratio is adjusted according to the type of polyolefin. PP materials require a higher blowing ratio to improve the degree of orientation.

[0030] The surface layer, the tearable light-blocking layer and the inner layer are laminated using dry or solvent-free methods.

[0031] As a preferred embodiment, the outer layer adopts dry lamination and the inner layer adopts solvent-free lamination. Both can be laminated with polyurethane composite glue. The glue amount of dry lamination is 2-5g / m2 The glue amount of solvent-free composite is 0.8-2 g / m 2 .

[0032] As a preferred embodiment, the glue amount of dry compound is 3-4g / m 2 The glue amount of solvent-free composite is 1.2-1.6 g / m 2 .

[0033] The difference between dry lamination and solvent-free lamination is that the composite glue in dry lamination contains 30-70% organic solvent, such as ethyl acetate; while solvent-free lamination is 100% solid content polyurethane composite glue.

[0034] In a second aspect, the present invention also provides an application and preparation method of a packaging sheet having at least one of the above technical features, wherein the steps of the preparation process include: S1, preparing the surface layer, the tearable light-blocking layer and the inner layer respectively; S2, compounding the three layers of materials in sequence using a dry or solvent-free compounding process; As a preferred embodiment, it also includes S3, where a printing ink layer is provided between the surface layer and the tearable light-blocking layer, and the printing ink layer can be printed by gravure printing or flexographic printing.

[0035] Among them, the better one adopts flexographic printing, and the printing repeatability deviation is controlled within the range of ±2%.

[0036] Specifically, a servo motor-driven flexographic printing press is used, the printing pressure is controlled at 0.15-0.25 MPa, the drying temperature is 60-80°C, the printing ink is water-based polyurethane ink, and the curing energy is 150-200 mJ / cm 2 .

[0037] The sheet material made according to at least one of the above technical features can be used for packaging of liquid food, medicine or cosmetics. The molding methods in different packaging machines include blister molding or blow molding, the molding temperature is 120-135°C, and the molding time is 2-5s.

[0038] The advantages and beneficial effects of the present invention are: through the three-layer composite structure design, the packaging material includes a surface layer, an easy-tear light-blocking layer and an inner high-barrier easy-tear layer stacked in sequence, the surface layer adopts a stretchable cast CPP or DPET film, the easy-tear light-blocking layer is a PP / PE and COC blended material containing a light-blocking agent, and the inner layer is a co-extruded blown film structure of more than 7 layers and contains an EVOH barrier layer.

[0039] The packaging material presented in this invention combines high barrier properties with easy tearing and stable molding. EVOH provides excellent oxygen barrier properties, while the COC blend ensures easy tearing performance. The multi-layer coextrusion structure ensures molding quality. The printable surface layer meets aesthetic requirements, while the optimized lamination process ensures interlayer bonding strength while also meeting environmental requirements. This material is particularly suitable for packaging fluid products that require both high barrier properties and easy opening. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the structure of the fluid material packaging sheet of the present invention; Figure 2 It is a schematic structural diagram of the inner layer of the packaging sheet of the present invention. DETAILED DESCRIPTION

[0041] The following embodiments are further described in conjunction with the accompanying drawings and examples. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0042] Example 1: A liquid cheese packaging sheet, the structural components of which are arranged in order: Surface layer: DPET film with a thickness of 12 μm; Printing layer: Flexographic printing ink layer, printing repeat length deviation ≤ 2%; First composite adhesive layer: polyurethane dry composite adhesive, adhesive amount 3.5 g / m 2 ; Easy-tear light-blocking layer: It is set up as a three-layer sandwich structure of HOPP / COPP+COC / HOPP in sequence. The COC content in the middle layer is 20%, and it is mixed with 10% light-blocking agent of the total mass of the easy-tear light-blocking layer. The total thickness is 140 μm; the mass ratio of the sum of the two layers of HOPP to COPP here is 3:7.

[0043] Second composite adhesive layer: polyurethane solvent-free composite adhesive, adhesive amount 1.5 g / m 2 ; Inner layer: 7-layer co-extruded blown film structure with a total thickness of 50 μm, consisting of PE / PE+7.5% COC / adhesive layer / EVOH (5 μm) / adhesive layer / PE+7.5% COC / PE.

[0044] The preparation method of the packaging sheet comprises the following steps: S1, surface layer preparation: 12 μm thick DPET film was prepared by casting process; S2, printing: an ink layer is attached to one side of the surface layer by flexographic printing; S3, preparation of the tearable light-blocking layer: A: HOPP, B: COPP, COC, titanium dioxide; the two film layers are melt-extruded in three layers in an A / B / A structure through an extruder, and then formed into one piece by blown film; the titanium dioxide addition amount is 10%, and the particle size is 50nm; S4, inner layer preparation: using a co-extrusion blown film machine with more than 7 layers, at a blow-up ratio of 3.0 and a processing temperature of 180-220°C, blown film is formed into an integrated structure of PE / PE+COC / adhesive layer / EVOH / adhesive layer / PE+COC / PE; the adhesive layer uses MAH-g-PE with a grafting rate of 1.2% and a thickness of 5μm.

[0045] S5, composite process: dry composite is used to prepare a first composite adhesive layer between the surface layer and the tearable light-blocking layer to connect the two, and then solvent-free composite is used to prepare a second composite adhesive layer between the tearable light-blocking layer and the inner layer to connect the composite sheets into one.

[0046] Liquid cheese packaging was obtained by using a square forming mold in a UNIFILL packaging machine at a preheated temperature of 120°C for 2 seconds.

[0047] Example 2 A liquid medicine packaging sheet, the structural components of which are arranged in order: Surface layer: DPET film with a thickness of 23 μm; Printing layer: Flexographic printing ink layer, printing repeat length deviation ≤ 2%; First composite adhesive layer: polyurethane dry composite adhesive, adhesive amount 2.0 g / m 2 ; Easy-tear light-blocking layer: It is set up as a three-layer sandwich structure of HOPP / COPP+COC / HOPP in sequence. The COC content in the middle layer is 20%, and it is mixed with 12% light-blocking agent of the total mass of the easy-tear light-blocking layer. The total thickness is 120 μm; the mass ratio of the sum of the two layers of HOPP to COPP here is 7:3.

[0048] Second composite adhesive layer: polyurethane solvent-free composite adhesive, adhesive amount 0.8 g / m 2 ; Inner layer: 7-layer co-extruded blown film structure with a total thickness of 50 μm, consisting of PE / PE+10% COC / adhesive layer / EVOH (5 μm) / adhesive layer / PE+10% COC / PE.

[0049] The preparation method of the packaging sheet comprises the following steps: S1, surface layer preparation: 23 μm thick DPET film was prepared by casting process; S2, printing: an ink layer is attached to one side of the surface layer by flexographic printing; S3, preparation of the tearable light-blocking layer: A: HOPP, B: COPP, COC, carbon black; the two film layers are melt-extruded in three layers in an A / B / A structure through an extruder, and then formed into a whole by blown film forming; the carbon black addition amount is 12%, and the particle size is 80nm; S4, inner layer preparation: using a co-extrusion blown film machine with more than 7 layers, at a blow-up ratio of 3.5 and a processing temperature of 180-220°C, blown film is formed into an integrated structure of PE / PE+COC / adhesive layer / EVOH / adhesive layer / PE+COC / PE; the adhesive layer uses MAH-g-PE with a grafting rate of 0.8% and a thickness of 3μm; S5, composite process: dry composite is used to prepare a first composite adhesive layer between the surface layer and the tearable light-blocking layer to connect the two, and then solvent-free composite is used to prepare a second composite adhesive layer between the tearable light-blocking layer and the inner layer to connect the composite sheets into one.

[0050] In the Chunguang packaging machine, a circular molding die is used and preheated to 120°C for 2 seconds to obtain liquid medicine packaging.

[0051] Example 3 A liquid cosmetic packaging sheet, the structural components of which are arranged in order: Surface layer: DPET film with a thickness of 12 μm; Printing layer: Flexographic printing ink layer, printing repeat length deviation ≤ 2%; First composite adhesive layer: polyurethane dry composite adhesive, adhesive amount 5.0 g / m 2 ; Easy-to-tear light-blocking layer: It is set up as a three-layer sandwich structure of HOPP / COPP+COC / HOPP in sequence. The COC content in the middle layer is 20%, and it is mixed with 12% light-blocking agent of the total mass of the easy-to-tear light-blocking layer. The total thickness is 120 μm; the mass ratio of the sum of the two layers of HOPP to COPP here is 6:4.

[0052] Second composite adhesive layer: polyurethane solvent-free composite adhesive, adhesive amount 0.8 g / m 2 ; Inner layer: 7-layer co-extrusion blown film structure with a total thickness of 50 μm, consisting of PP / PP+8% COC / adhesive layer / EVOH (8 μm) / adhesive layer / PP+8% COC / PP.

[0053] The preparation method of the packaging sheet comprises the following steps: S1, surface layer preparation: 12 μm thick DPET film was prepared by casting process; S2, printing: an ink layer is attached to one side of the surface layer by flexographic printing; S3, preparation of the tearable light-blocking layer: A: HOPP, B: COPP, COC, titanium dioxide; the two film layers are melt-extruded in three layers with an A / B / A structure through an extruder, and then formed into one piece by blown film; the titanium dioxide addition amount is 15%, and the particle size is 50nm; S4, inner layer preparation: using a co-extrusion blown film machine with more than 7 layers, at a blow-up ratio of 3.5 and a processing temperature of 180-220°C, blown film is formed into an integrated structure of PP / PP+COC / adhesive layer / EVOH / adhesive layer / PP+COC / PP; the adhesive layer uses MAH-g-PP with a grafting rate of 0.8% and a thickness of 8μm; S5, composite process: dry composite is used to prepare a first composite adhesive layer between the surface layer and the tearable light-blocking layer to connect the two, and then solvent-free composite is used to prepare a second composite adhesive layer between the tearable light-blocking layer and the inner layer to connect the composite sheets into one.

[0054] In the Youtianyuan packaging machine, a special-shaped molding mold is used, and the molding temperature is preheated to 135°C for 2 seconds to obtain liquid cosmetic packaging.

[0055] Example 4 A liquid food packaging sheet, the structural components of which are arranged in order: Surface layer: CPP film with a thickness of 40 μm; Printing layer: Flexographic printing ink layer, printing repeat length deviation ≤ 2%; First composite adhesive layer: polyurethane dry composite adhesive, adhesive amount 2.0 g / m 2 ; Easy-tear light-blocking layer: It is set up as a three-layer sandwich structure of HOPP / COPP+COC / HOPP in sequence. The COC content in the middle layer is 25%, and it is mixed with 15% light-blocking agent of the total mass of the easy-tear light-blocking layer. The total thickness is 120 μm; the mass ratio of the sum of the two layers of HOPP to COPP is 5:5.

[0056] Second composite adhesive layer: polyurethane solvent-free composite adhesive, adhesive amount 1.6 g / m 2 ; Inner layer: 7-layer co-extrusion blown film structure with a total thickness of 50 μm, consisting of PP / PP+12% COC / adhesive layer / EVOH (10 μm) / adhesive layer / PP+12% COC / PP.

[0057] The preparation method of the packaging sheet comprises the following steps: S1, surface layer preparation: CPP film with a thickness of 40 μm was prepared by tape casting process; S2, printing: an ink layer is attached to one side of the surface layer by flexographic printing; S3, preparation of the tearable light-blocking layer: A: HOPP, B: COPP, COC, carbon black; the two film layers are melt-extruded in three layers in an A / B / A structure through an extruder, and then formed into one piece by blown film; the carbon black addition amount is 15%, and the particle size is 100nm; S4, inner layer preparation: using a co-extrusion film blowing machine with more than 7 layers, at a blow-up ratio of 2.5 and a processing temperature of 190-240°C, blown film is formed into an integrated structure of PP / PP+COC / adhesive layer / EVOH / adhesive layer / PP+COC / PP; the adhesive layer uses MAH-g-PP with a grafting rate of 1.2% and a thickness of 5μm.

[0058] S5, composite process: dry composite is used to prepare a first composite adhesive layer between the surface layer and the tearable light-blocking layer to connect the two, and then solvent-free composite is used to prepare a second composite adhesive layer between the tearable light-blocking layer and the inner layer to connect the composite sheets into one.

[0059] In the Youtianyuan packaging machine, a special-shaped forming mold is used, and the forming process is performed at a preheating temperature of 135°C for 2 seconds to obtain liquid food packaging.

[0060] The technical effects of the above embodiments were tested. The tear strength was measured according to ASTM D1922 in a universal testing machine with a crosshead speed of 250 mm / min, a sample size of 100×63 mm, and a pre-cut of 15 mm. The flexural modulus was measured according to ASTM D790 using a three-point bending method with a sample size of 80×10×total thickness (mm), a span of 64 mm, and a rate of 2 mm / min. The thermoforming shrinkage was measured according to ISO 11501 with a sample size of 100×100 mm and free heating.

[0061] The light transmittance was measured in a spectrophotometer using an integrating sphere method in a wavelength range of 400-700 nm according to ASTM D1003. Each embodiment can achieve a light transmittance of less than 5%. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A fluid material packaging sheet, characterized in that: It includes a surface layer, an easy-to-tear light-blocking layer and an inner layer stacked in sequence. The surface layer is a CPP or DPET film produced by a casting process; The tearable light-blocking layer is a blend of PP or PE and COC containing a light-blocking agent; The inner layer is a co-extruded blown film structure of more than 7 layers, including an EVOH barrier layer; The surface layer, the tearable light-blocking layer and the inner layer are bonded by dry lamination or solvent-free lamination process.

2. The packaging sheet according to claim 1, characterized in that The surface layer is a CPP film or a DPET film, wherein: The CPP film meets the following requirements: thickness 20-70 μm, elongation at break ≥ 600%, haze ≤ 8%, thickness deviation ≤ 3%; The DPET film meets the following requirements: thickness 10-40 μm, elongation at break ≥ 300%, haze ≤ 2%, and thickness deviation ≤ 2%.

3. The packaging sheet according to claim 1, characterized in that The tearable light-blocking layer contains, by weight, no less than 10% of the light-blocking agent and 20-30% of the COC of the total mass of the tearable light-blocking layer. The light transmittance of the tearable light-blocking layer is less than 5%, and the thickness is 60-200 μm.

4. The packaging sheet according to claim 1, wherein The structure of the inner layer is stacked in sequence from the outside to the inside: Polyolefin, polyolefin + COC, adhesive layer, EVOH, adhesive layer, polyolefin + COC, polyolefin; The polyolefin is selected from PP and / or PE, the EVOH layer thickness is ≥5 μm, the COC accounts for ≥15% of the total mass of the inner layer, and the total thickness of the inner layer is 40-100 μm.

5. The packaging sheet according to claim 1, characterized in that The surface layer and the tearable light-blocking layer are compounded in a dry manner, and the tearable light-blocking layer and the inner layer are compounded in a solvent-free manner. The components of the composite glue used in the two compounding processes both include polyurethane.

6. The packaging sheet according to claim 1, characterized in that A printing ink layer is provided between the surface layer and the tearable light-blocking layer, and a flexographic or gravure printing process is adopted, with a printing repeat length deviation of ≤2%.

7. The packaging sheet according to claim 1, characterized in that The polyolefin material of the inner layer is selected from: Density is 0.88-0.92g / cm 3 Polypropylene of a blend of COPP and HOPP; and / or, Density 0.86-0.91g / cm 3 Polyethylene blend of PE and ionomer.

8. A method for preparing the packaging material according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1, preparing the surface layer, the tearable light-blocking layer and the inner layer respectively; S2, compounding the three layers of materials in sequence using a dry or solvent-free compounding process.

9. The preparation method according to claim 8, characterized in that The inner layer co-extrusion blown film is produced by a co-extrusion blown film machine with more than 7 layers, and the processing temperature range is 150-240°C.

10. Use of the packaging material according to any one of claims 1 to 7, characterized in that: Used for packaging of liquid food, medicine or cosmetics. The molding method is blister molding or blow molding, and the molding temperature is 120-135℃.

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