Heat-resistant bowl cover and preparation method thereof

Abstract

The invention discloses a heat-resistant bowl cover and a preparation method thereof, and relates to the technical field of instant food packaging. The heat-resistant bowl cover comprises a surface layer, a bonding layer, a blocking layer and a heat sealing layer which are sequentially arranged from top to bottom, wherein the surface layer comprises PP synthetic paper. The PP synthetic paper comprises the following components: polypropylene resin, an inorganic filler and a non-fluorescent physical whitening agent. The inorganic filler is calcium carbonate and accounts for 20-40% of the weight of the PP synthetic paper; the non-fluorescent physical whitening agent is titanium dioxide, and the non-fluorescent physical whitening agent accounts for 1.5-4.5% of the PP synthetic paper in percentage by weight. According to the heat-resistant bowl cover and the preparation method thereof, due to the fact that the PP synthetic paper is used, compared with an existing bowl cover containing paper, the heat-resistant bowl cover is not prone to pattern lost points, low in printing rejection rate, higher in heat resistance, good in high-temperature (190 DEG C or above) heat sealing flatness and free of blistering.

Description

Technical Field

[0001] The present invention relates to the technical field of convenient food packaging, and particularly relates to a heat-resistant bowl cover and a preparation method thereof. Background Art

[0002] In the technical field of convenient food packaging, the sealing performance and heat resistance of container lid materials are key factors to ensure food safety and product appearance quality. Currently, the common lid materials on the market mostly use paper-plastic composite materials, which have the advantages of low cost and good degradability, meeting the environmental protection trend. However, such lid materials containing paper expose significant technical defects in the high-temperature heat-sealing process.

[0003] As shown in Chinese Patent CN207156622U for the currently used paper-containing materials, paper lid materials naturally contain moisture due to their fiber structure. When heat-sealed under high temperature and pressure by a heat-sealing machine, the internal moisture rapidly vaporizes to form local high-pressure steam. This phenomenon directly leads to delamination of the lid material and surface bubbling, damaging the appearance integrity of the packaging.

[0004] Based on the above technical contradictions, there is an urgent need to develop a heat-resistant paperless lid material solution to solve the problems existing in the existing material system. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a heat-resistant bowl cover and a preparation method thereof.

[0006] Specifically, it includes the following technical solutions:

[0007] In a first aspect, a heat-resistant bowl cover is provided, which includes a surface layer, an adhesive layer, a barrier layer, and a heat-sealing layer arranged in sequence from top to bottom. The surface layer includes PP synthetic paper (PP: polypropylene).

[0008] Among them, PP synthetic paper is an important differentiator of the present invention from the existing paper-containing bowl covers. Paper lid materials naturally contain moisture due to their fiber structure. When heat-sealed under high temperature and pressure by a heat-sealing machine, the internal moisture rapidly vaporizes to form local high-pressure steam. This phenomenon directly leads to delamination of the lid material and surface bubbling, damaging the appearance integrity of the packaging. However, the essence of PP synthetic paper is a PP film, so the above problems will not occur, and thus it can adapt to higher heat-sealing temperatures.

[0009] Furthermore, the PP synthetic paper includes the following components: polypropylene resin, inorganic filler, and non-fluorescent physical brightening agent.

[0010] Furthermore, the inorganic filler is calcium carbonate, and the weight percentage of the inorganic filler in the PP synthetic paper is 20 - 40%; the non-fluorescent physical brightening agent is titanium dioxide, and the weight percentage of the non-fluorescent physical brightening agent in the PP synthetic paper is 1.5 - 4.5%.

[0011] Further, the density of the PP synthetic paper is 0.6 - 0.95 g / cm 3 , and the thickness is 30 - 100 μm.

[0012] Preferably, the whiteness of the PP synthetic paper is ≥70%, both sides are corona treated, and the surface tension of both sides is ≥38 dynes.

[0013] Further, the surface layer includes a PET layer (PET: polyethylene terephthalate), an ink layer, an adhesive layer, and a PP synthetic paper arranged in sequence from top to bottom.

[0014] Further, the surface layer includes a varnish layer, an ink layer, and a PP synthetic paper arranged in sequence from top to bottom.

[0015] Among them, for commercially available paper bowl lids, the surface layer structure generally includes the following two implementation forms:

[0016] 1) "PET / Ink / Adhesive / Paper" (PET is printed and then laminated to the paper)

[0017] This implementation form requires two processes of printing and lamination, while if the surface layer in the present invention adopts the structure of varnish layer - ink layer - PP synthetic paper, only one printing process is needed, and the cost is lower than that of existing products.

[0018] 2) "Varnish / Ink / Paper" (ink and varnish are printed on the paper)

[0019] Although this implementation form only requires the printing process, using the paper as the printing film is prone to pattern missing points, with a high printing rejection rate, which poses high requirements for printing control. However, the PP synthetic paper used in the present invention is a plastic film and is not prone to pattern missing points.

[0020] Further, the adhesive layer is one or more of polyurethane adhesives and polyethylene resins.

[0021] Preferably, the adhesive layer is a composite laminate of glue (polyurethane adhesive) and LDPE (polyethylene resin), that is, the interlayer structure formula is "glue / LDPE", and the adhesive layer plays a role in bonding the surface layer and the barrier layer.

[0022] Further, the barrier layer is at least one of a composite film of PET and aluminum foil, aluminum foil, aluminized PET, and aluminized OPP (OPP: o-phenylphenol).

[0023] Further, the heat-sealing layer is one or more of polyurethane adhesives, extrusion coating resins, and dry-laminated PE films (PE: polyethylene).

[0024] Preferably, the coating resin is one or more of LDPE resin (LDPE: low density polyethylene), EMA resin (EMA: ethylene-methyl acrylate copolymer), EMAA resin (EMAA: ethylene-methyl methacrylate copolymer), EVA resin (EVA: ethylene-vinyl acetate copolymer), and PE resin.

[0025] In a second aspect, there is provided a method for preparing the heat-resistant bowl lid as described in the first aspect, comprising the following steps:

[0026] S1. Prepare the surface layer using a printing press and / or a dry laminator;

[0027] S2. Use a coating machine to coat an adhesive layer on one side of the PP synthetic paper in the surface layer, and laminate a barrier layer on the side of the adhesive layer away from the surface layer;

[0028] S3. Use a coating machine or a dry laminator to prepare a heat-sealing layer on the side of the barrier layer away from the adhesive layer to obtain a semi-finished bowl lid roll film;

[0029] S4. Use a die-cutting machine to cut out the outer contour of the bowl lid on the semi-finished bowl lid roll film to obtain the heat-resistant bowl lid.

[0030] Preferably, step S1 is to print an ink layer on the PET layer using a printing press to obtain a first laminate, and then use a dry laminator to laminate the side of the ink layer in the first laminate to the PP synthetic paper through an adhesive layer to obtain the surface layer.

[0031] Preferably, step S1 is to directly print an ink layer on the PP synthetic paper and then print a varnish layer on the ink layer to obtain the surface layer.

[0032] Preferably, step S2 is to apply glue on the side of the surface layer close to the PP synthetic paper using the gluing part of the coating machine, then coat the adhesive layer on the gluing surface to obtain a second laminate, and finally use the lamination part of the coating machine to laminate the coated side of the second laminate to the barrier layer to obtain a third laminate.

[0033] Preferably, step S3 is to coat a heat-sealing layer on the side of the third laminate close to the barrier layer using a coating machine to obtain the semi-finished bowl lid roll film.

[0034] Preferably, step S3 is to laminate the side of the third laminate close to the barrier layer to the heat-sealing layer (dry-laminated PE film) using a dry laminator to obtain the semi-finished bowl lid roll film.

[0035] The beneficial effects of the present invention are as follows:

[0036] The present invention provides a heat-resistant bowl lid and a preparation method thereof. Since PP synthetic paper is used, compared with the existing paper-containing bowl lids, there are fewer missing dots in the pattern, the printing rejection rate is low, the heat resistance is stronger, and the heat sealing flatness is good and there are no bubbles at high temperatures (above 190°C). BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0038] Figure 1 Structural schematic diagram of the heat-resistant bowl lid of Embodiment 1 of the present invention;

[0039] Figure 2 Structural schematic diagram of the surface layer of the heat-resistant bowl lid of Embodiment 1 of the present invention;

[0040] Figure 3 Structural schematic diagram of the surface layer of the heat-resistant bowl lid of Embodiment 4 of the present invention;

[0041] Explanation of the labels in the figure:

[0042] 1 - surface layer; 2 - adhesive layer; 3 - barrier layer; 4 - heat-sealing layer; 5 - varnish layer; 6 - ink layer; 7 - z-PP synthetic paper; 8 - PET layer; 9 - adhesive layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] The following will clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0044] It should be understood that when used in this specification and the appended claims, the terms "comprises" and "comprising" indicate the presence of the described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or their combinations.

[0045] It should also be understood that the terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in this specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include the plural forms.

[0046] It should be further understood that the term "and / or" used in the specification and appended claims of the present invention refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0047] To more fully understand the technical content of the present invention, the technical solutions of the present invention will be further introduced and described below in conjunction with specific embodiments.

[0048] Example 1

[0049] As Figure 1 shown, a heat-resistant bowl cover includes a surface layer 1, an adhesive layer 2, a barrier layer 3, and a heat-sealing layer 4 arranged in sequence from top to bottom. The surface layer 1 includes PP synthetic paper 7z.

[0050] The PP synthetic paper 7z includes the following components: polypropylene resin, inorganic filler, and non-fluorescent physical brightener. Among them, the inorganic filler is calcium carbonate, and the inorganic filler accounts for 30% by weight of the PP synthetic paper 7z; the non-fluorescent physical brightener is titanium dioxide, and the non-fluorescent physical brightener accounts for 3% by weight of the PP synthetic paper 7z. The density of the PP synthetic paper is 0.9 g / cm 3 , and the thickness is 45 μm. Both sides of the PP synthetic paper 7z are corona-treated, and the surface tension of both sides is ≥ 38 dynes (specifically, the dyne value of the printing surface is 44, and the dyne value of the non-printing surface is 38).

[0051] Figure 2 is a schematic diagram of the surface layer structure of the heat-resistant bowl cover of Example 1 of the present invention. The surface layer 1 includes a varnish layer 5, an ink layer 6, and PP synthetic paper 7z arranged in sequence from top to bottom. The adhesive layer 2 is polyethylene resin (specifically LDPE resin produced by Yanshan Petrochemical). The barrier layer 3 is aluminum foil. The heat-sealing layer 4 is composed of LDPE resin and polyethylene resin (PE resin).

[0052] The preparation method of the heat-resistant bowl cover includes the following steps:

[0053] S1. Use a printing press to directly print the ink layer 6 on the PP synthetic paper 7z (with a thickness of 45 μm and a density of 0.9 g / cm 3 ) to obtain the first laminate, and then print the varnish layer 5 on the ink layer 6 (of the first laminate) to obtain the surface layer 1;

[0054] S2. Use the gluing part of a laminating machine to apply glue to one side of the surface layer 1 close to the PP synthetic paper 7z, and then laminate the adhesive layer 2 (using LDPE resin produced by Yanshan Petrochemical, with a lamination thickness of 20 μm) on the glued surface to obtain the second laminate. Finally, use the compounding part of the laminating machine to compound the laminated side of the second laminate with the barrier layer 3 (selecting aluminum foil with a thickness of 7 μm) together to obtain the third laminate;

[0055] S3. Use a film laminating machine to laminate the heat-sealing layer 4 on one side of the third laminate close to the barrier layer 3. Specifically, laminate a mixed resin (the mixed resin uses LDPE resin produced by Yanshan Petrochemical and LDPE resin produced by Ineos, and the weight ratio of the resins is Yanshan Petrochemical LDPE: Ineos LDPE = 6:1, and the lamination thickness is 20 μm), and then laminate a polyethylene resin (use the modified easily peelable PE resin produced by Tosoh Corporation, and the lamination thickness is 20 μm) to obtain a semi-finished bowl cover roll film;

[0056] S4. Use a die-cutting machine to cut out the outer contour of the bowl cover on the semi-finished bowl cover roll film to obtain a heat-resistant bowl cover.

[0057] Example 2 The difference between Example 2 and Example 1 is that the density of the PP synthetic paper in Example 2 is 0.8 g / cm 3 , and the other conditions are the same.

[0058] Example 3 The difference between Example 3 and Example 1 is that the density of the PP synthetic paper in Example 3 is 0.7 g / cm 3 , and the other conditions are the same.

[0059] Example 4

[0060] Figure 3 This is a schematic diagram of the surface layer structure of the heat-resistant bowl cover in Example 4 of the present invention. The difference between Example 4 and Example 1 is that the surface layer of Example 4 includes a PET layer 8, an ink layer 6, an adhesive layer 9, and a PP synthetic paper 7z arranged in sequence from top to bottom. In step S1 of the preparation method of the heat-resistant bowl cover in Example 4, use a printing machine to print the ink layer 6 on the PET layer 8 (12 μm) to obtain a first laminate, and then use a dry laminating machine to laminate the side of the ink layer 6 in the first laminate to the PP synthetic paper 7z through the adhesive layer 9 to obtain the surface layer, and the other conditions are the same. Among them, the adhesive layer 9 uses a one-component solvent-free polyurethane adhesive.

[0061] Example 5

[0062] Compared with Example 1, the difference in Example 5 is that the heat-sealing layer is a dry-laminated PE film (an easily peelable dry-laminated PE film, with a thickness of 60 μm, provided by Yongsheng Yunjia). In the preparation method of the heat-resistant bowl cover in Example 5, in step S3, use a dry laminating machine to laminate the side of the third laminate close to the barrier layer to the heat-sealing layer (dry-laminated PE film) to obtain a semi-finished bowl cover roll film, and the other conditions are the same.

[0063] Comparative Example 1

[0064] Compared with Example 4, the difference in Comparative Example 1 is that a single-sided copperplate paper (with a grammage of 80 g / m2 , APP production) is used to replace the PP synthetic paper, and the other conditions are the same.

[0065] Comparative Example 2

[0066] Compared with Example 1, the difference in Comparative Example 2 is that single-sided coated paper (gram weight is 80 g / m 2 , APP production) is used to replace the PP synthetic paper, and the other conditions are the same.

[0067] Comparative Example 3

[0068] Compared with Example 1, the difference in Comparative Example 3 is that the weight percentage of the non-fluorescent physical brightening agent in the PP synthetic paper is 1%, and the other conditions are the same.

[0069] Comparative Example 4

[0070] Compared with Example 1, the difference in Comparative Example 4 is that the weight percentage of the non-fluorescent physical brightening agent in the PP synthetic paper is 5%, and the other conditions are the same.

[0071] Comparative Example 5

[0072] Compared with Example 1, the difference in Comparative Example 5 is that neither side of the PP synthetic paper is corona-treated, and the surface tension of both sides is ≥ 38 dynes (specifically, the dyne value of the printing surface is 38, and the dyne value of the non-printing surface is 38), and the other conditions are the same.

[0073] Performance test:

[0074] I. Printing appearance evaluation and whiteness test:

[0075] 1) Printing appearance evaluation

[0076] Take the examples and comparative examples, and observe the printed patterns on the PP synthetic paper under a standard light source using a magnifying glass. Grade them according to the severity of pattern dot loss: Grade 0 (less or basically no dot loss), Grade 1 (slight dot loss), Grade 2 (severe dot loss).

[0077] 2) Whiteness test

[0078] Take the original film of the PP synthetic paper used in the examples and comparative examples, cut it into 50 mm × 50 mm specimens, with the surface clean and no creases. Use a whiteness meter, calibrate it to the reference value with a standard white board after preheating for 30 minutes. Cover the specimen flat on the test hole to avoid environmental light interference;

[0079] Record the blue light whiteness value (R457) displayed by the instrument. Measure 3 different areas for each sample and take the arithmetic mean.

[0080] The test results of the heat-resistant bowl lids in Example 1 and Comparative Examples 1-4 are shown in Table 1 below: (INK is used to represent the ink).

[0081] Table 1 Printing Appearance Evaluation and Whiteness Test Results of Heat-resistant Bowl Lids in Example 1 and Comparative Examples 1-4

[0082]

[0083]

[0084] From the test results in Table 1, it can be seen that if a single-sided coated paper is used instead of PP synthetic paper to make the heat-resistant bowl lid (Comparative Example 2), slight dot loss will occur. In addition, if PP synthetic paper with the weight percentage of fluorescent physical brightener outside the scope defined in the present invention is used to make the heat-resistant bowl lid (Comparative Examples 3 and 4), the whiteness will be < 70% or serious dot loss will occur.

[0085] II. Heat-sealing Flatness and Blistering Test:

[0086] Take a bucket-type instant noodle bowl with an inner layer laminated with PE resin, and tear off the outer wall fan blades.

[0087] Take the examples and comparative examples, and use a capping machine to seal the above examples, comparative examples and the bucket-type instant noodle bowls filled with noodles (heat-sealing parameters: 190 - 200 °C / 1 s / 0.4 MPa). After waiting for the heat-sealed part of the bowl lid to cool, observe the surface flatness of the heat-sealed part under a standard light source, and record whether there are heat-induced blisters on the surface of the bowl lid.

[0088] Judgment criteria: Grade according to the severity of orange peel phenomenon: Grade 0 (none), Grade 1 (slight wrinkles), Grade 2 (severe wrinkles); Grade according to whether there are heat-induced blisters on the surface of the bowl lid: OK (no heat-induced blisters), NG (presence of heat-induced blisters);

[0089] Perform heat-sealing flatness and blistering tests on the heat-resistant bowl lids of Examples 1-4 and Comparative Example 1, and the test results are shown in Table 2 below (using INK to represent the ink):

[0090] Table 2 Heat-sealing Flatness and Blistering Test Results of Heat-resistant Bowl Lids in Examples 1-4 and Comparative Example 1

[0091]

[0092]

[0093] From the test results in Table 2, it can be seen that heat-resistant bowl lids made of PP synthetic paper with different densities (Examples 2 and 3) have wrinkling phenomena, and this wrinkling phenomenon is a special process form (such as making orange peel touch, etc.). If a single-sided coated paper is used instead of PP synthetic paper to make the heat-resistant bowl lid (Comparative Example 1), blistering will occur.

[0094] III. Ink Adhesion Test

[0095] Take the finished bowl lids of the examples and comparative examples, place them in an environment of 23 ± 2°C and 50% RH for 24 hours, cut 100 mm × 25 mm specimens, use 3M 600 tape (width ≥ 25 mm, adhesive force 10 ± 1 N / 25 mm), closely attach the tape to the printing area, after standing for 60 seconds, quickly peel off the tape in the 180° direction, and then use standard grid paper to calculate the ink peeling area; repeat 3 times, replacing the tape with a new one each time.

[0096] Perform ink peeling tests on the heat-resistant bowl lids of Example 1 and Comparative Example 5. The test results are shown in Table 3 below:

[0097] Table 3 Ink Peeling Test Results of Heat-Resistant Bowl Lids of Example 1 and Comparative Example 5

[0098] Example / Comparative Example Ink peeling area Example 1 ＜10％ Comparative Example 5 ＞10％

[0099] It can be seen from the test results in Table 3 that for the heat-resistant bowl lid made of PP synthetic paper without corona treatment (Comparative Example 5), the ink peeling area is relatively large.

[0100] In summary, the present invention provides a heat-resistant bowl lid and its preparation method. Due to the use of PP synthetic paper, compared with the existing paper-containing bowl lids, pattern missing points are not likely to occur, the printing rejection rate is low, the heat resistance is stronger, and the heat sealing flatness is good and no bubbles occur at high temperatures (above 190°C).

[0101] As described above, the above are only the specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A heat-resistant bowl cover, characterized in that: It comprises a surface layer, an adhesive layer, a barrier layer and a heat-sealing layer which are arranged in sequence from top to bottom, and the surface layer comprises PP synthetic paper.

2. The heat-resistant bowl cover according to claim 1, characterized in that: The PP synthetic paper comprises the following components: polypropylene resin, inorganic filler and non-fluorescent physical brightener.

3. The heat-resistant bowl cover according to claim 2, characterized in that: The inorganic filler is calcium carbonate, and the weight percentage of the inorganic filler in the PP synthetic paper is 20-40%; the non-fluorescent physical brightener is titanium dioxide, and the weight percentage of the non-fluorescent physical brightener in the PP synthetic paper is 1.5-4.5%.

4. The heat-resistant bowl cover according to claim 2, characterized in that: The density of the PP synthetic paper is 0.6-0.95 g / cm 3 , thickness is 30-100μm.

5. The heat-resistant bowl cover according to claim 1, characterized in that: The surface layer comprises a PET layer, an ink layer, an adhesive layer and PP synthetic paper which are arranged in sequence from top to bottom.

6. The heat-resistant bowl cover according to claim 1, characterized in that: The surface layer comprises a varnish layer, an ink layer and PP synthetic paper which are arranged in sequence from top to bottom.

7. The heat-resistant bowl cover according to claim 1, characterized in that: The adhesive layer is one or more of polyurethane adhesive and polyethylene resin.

8. The heat-resistant bowl cover according to claim 1, characterized in that: The barrier layer is at least one of a composite film of PET and aluminum foil, aluminum foil, aluminum-plated PET, and aluminum-plated OPP.

9. The heat-resistant bowl cover according to claim 1, characterized in that: The heat sealing layer is one or more of polyurethane adhesive, coating resin and dry laminated PE film.

10. The method for preparing a heat-resistant bowl cover according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1. Prepare the surface layer using a printing press and / or a dry compounding machine; S2. Laminating an adhesive layer on one side of the PP synthetic paper in the surface layer using a laminating machine, and compounding a barrier layer on the side of the adhesive layer away from the surface layer; S3. Using a laminating machine or a dry laminating machine to prepare a heat sealing layer on the side of the barrier layer away from the adhesive layer to obtain a semi-finished bowl cover roll film; S4. Use a punching machine to punch out the outer contour of the bowl cover on the semi-finished bowl cover roll film to obtain a heat-resistant bowl cover.

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