High-barrier heat-shrinkable film and preparation method thereof

Abstract

The invention discloses a high-barrier heat-shrinkable film and a preparation method thereof, relates to the field of packaging materials, and aims to solve the problems of high recovery difficulty of a composite film and low performance of a single-material film in the prior art. At least one of the rigid dihydric alcohols is cyclic dihydric alcohol. Furandicarboxylic acid or a derivative thereof is used as a main chain and is subjected to polycondensation with rigid dihydric alcohol, so that a dual-rigid structure can be formed, the glass transition temperature is increased, and high heat resistance and high stability are realized; the tetrabutyl titanate-zinc oxide composite catalyst has low heavy metal residue, can shorten the migration path of small molecules by improving the vacuum degree, and can be used for food and medicine packaging. The high-barrier heat-shrinkable film is made of a single-component material, and can be directly recovered in one way when being recovered after being used, so that the recovery is convenient.

Description

Technical Field

[0001] This invention relates to the field of packaging materials technology, specifically to a high-barrier heat-shrinkable film and its preparation method. Background Technology

[0002] Currently, high-barrier materials in the packaging field are mainly prepared by composite materials of multiple layers. Different material structures cannot be recycled using the same method after use.

[0003] Chinese patent CN109648976A discloses a co-extruded biaxially oriented PET / PPS composite film and its preparation method. The technical solution employs an ABA three-layer composite film, where layer A is modified PPS and layer B is modified PET. The modified PET is based on terephthalic acid, copolymerized by introducing dibasic acids such as naphthalenedicarboxylic acid and furanyl dicarboxylic acid, or diols such as propylene glycol and neopentyl glycol, to lower the glass transition temperature and match the compatibility with the modified PPS. Layer B has high water vapor permeability, requiring the addition of modified PPS in layer A to reduce permeability. Furthermore, layer B has a low glass transition temperature and limited heat resistance, necessitating the modification of PPS in layer A to improve its heat resistance. Additionally, the xylene extraction value of the overall low-molecular-weight compounds in layer B is 0.2%~0.42%, and its molecular migration properties prevent its direct use in food or medical packaging; the modification of PPS in layer A is needed to slow down this small molecule migration. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the existing defects and provide a high-barrier heat-shrinkable film and its preparation method, which can effectively solve the problems in the background art.

[0005] To achieve the above objectives, the present invention first discloses a high-barrier heat-shrinkable film. The technical solution adopted is that it is a single-layer copolyester film. The copolyester is obtained by copolymerizing furan dicarboxylic acid or its derivative with a rigid diol, wherein at least one of the rigid diols is a cyclic diol.

[0006] As a preferred embodiment of the present invention, the copolyester component has one of the following structures:

[0007] Furan dicarboxylic acid or its derivatives - neopentyl glycol - TMCD (2,2,4,4-tetramethyl-1,3-cyclobutanediol) copolyester:

[0008] ,

[0009] Furan dicarboxylic acid or its derivatives - isosorbide - TMCD copolyester:

[0010] ,

[0011] Furan dicarboxylic acid or its derivatives - isosorbide-neopentyl glycol copolyester:

[0012] .

[0013] By using furanyl dicarboxylic acid as the main chain, the strong polarity and planar rigidity of the furan ring can significantly improve the intermolecular forces, resulting in tight molecular packing and directly enhancing the material's barrier properties and chemical resistance. High barrier performance can be achieved through a single thin film. The steric hindrance of the furan ring and the cyclic diol can form a dual rigid structure, raising the glass transition temperature to above 90°C, thereby achieving high heat resistance and high stability.

[0014] This invention also discloses a method for preparing the above-mentioned high-barrier heat-shrinkable film, the technical solution of which includes the following steps:

[0015] Step 1: Mix furanyl dicarboxylic acid or its derivatives with a rigid diol, and add a catalyst and stabilizer to carry out a pre-condensation reaction;

[0016] Rigid diols are one or more of isosorbide, TMCD, and neopentyl glycol;

[0017] Step 2: Perform the final polycondensation reaction.

[0018] In a preferred embodiment of the present invention, the catalyst is a tetrabutyl titanate-zinc oxide composite catalyst. This catalyst can reduce heavy metal residues to below 1 ppm, meeting the safety standards for food contact materials, while simultaneously increasing catalytic efficiency by 20% and shortening the polycondensation time to 2-4 hours. The stabilizer is triphenyl phosphate.

[0019] As a preferred embodiment of the present invention, in step 1, the reaction temperature of the pre-condensation reaction is 180-220°C, and the reaction environment is protected by an inert gas to reduce monomer volatilization.

[0020] As a preferred technical solution of the present invention, in step 2, the reaction temperature of the final polycondensation reaction is 240-260℃, and the vacuum degree is below 50Pa, which improves the uniformity of molecular weight distribution. Furthermore, by using a higher vacuum degree, the extraction value of a single system containing 2,5-furandicarboxylic acid can be reduced to 0.2% or below. Moreover, due to the absence of multi-layer interfaces, the migration path of small molecules is shorter, resulting in better safety and making it more suitable for direct contact with food, medicine, and other applications.

[0021] As a preferred embodiment of the present invention, the mass proportions of diol, furanyl dicarboxylic acid or its derivatives, catalyst, and stabilizer are as follows:

[0022] 1.2-3 parts rigid diol, 1 part furanyl dicarboxylic acid or its derivative, 0.1-0.2 parts catalyst, and 0.015-0.025 parts stabilizer.

[0023] Compared with existing technologies, the beneficial effects of this invention are as follows: By using furanyl dicarboxylic acid or its derivatives as the main chain and polycondensing it with a rigid diol, this invention can form a double rigid structure, increasing the glass transition temperature and achieving high heat resistance and high stability. The tetrabutyl titanate-zinc oxide composite catalyst has low heavy metal residue, and by increasing the vacuum degree, it can shorten the migration path of small molecules, making it suitable for food and pharmaceutical packaging. The high-barrier heat-shrinkable film uses a single-component material, allowing for direct recycling through a single method after use, making recycling convenient. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1

[0026] This embodiment discloses the first implementation of the present invention, which first discloses a high-barrier heat-shrinkable film. The technical solution adopted is that it is a single-layer copolyester film composed of furanyl dicarboxylic acid-neopentyl glycol-TMCD copolyester, and the structural formula is shown below:

[0027] .

[0028] This invention also discloses a method for preparing the above-mentioned high-barrier heat-shrinkable film, the technical solution of which includes the following steps:

[0029] Step 1, Pre-polymerization,

[0030] One part of furanyl dicarboxylic acid, 0.6 parts of neopentyl glycol, 0.6 parts of TMCD, 0.08 parts of tetrabutyl titanate, 0.03 parts of zinc oxide, and 0.015 parts of triphenyl phosphate were mixed and subjected to a pre-condensation reaction at 180°C under helium protection. During the reaction, stirring was applied to ensure uniform mixing of monomers and catalysts, promote heat and mass transfer, and remove water by-products. The stirring speed was 50 rpm, a low speed, to avoid bumping of the system and facilitate a stable reaction under inert gas protection. The reaction time was 3 hours.

[0031] Step 2, final polycondensation,

[0032] The final polycondensation reaction was carried out at 260℃ and a vacuum of 50Pa. During the final polycondensation reaction, stirring was applied at 20 rpm. Low stirring speed was used under high vacuum to reduce the contact between the system and air, and to avoid the polymer chains from breaking due to excessive shear force. The reaction time was 2 hours.

[0033] Example 2

[0034] This embodiment discloses a second implementation of the present invention. Firstly, it discloses a high-barrier heat-shrinkable film. The technical solution adopted is a single-layer copolyester film composed of dimethyl furanate-isosorbitol-TMCD copolyester, with the following structural formula:

[0035] .

[0036] This invention also discloses a method for preparing the above-mentioned high-barrier heat-shrinkable film, the technical solution of which includes the following steps:

[0037] Step 1, Pre-polymerization,

[0038] One part of dimethyl furanate, 1.5 parts of isosorbide, 1.5 parts of TMCD, 0.12 parts of tetrabutyl titanate, 0.05 parts of zinc oxide, and 0.025 parts of triphenyl phosphate were mixed and subjected to a pre-condensation reaction at 220°C under argon protection. During the reaction, stirring was applied to ensure uniform mixing of monomers and catalysts, promote heat and mass transfer and discharge of the byproduct methanol. The stirring speed was 100 rpm, a low speed, to avoid bumping of the system and facilitate a stable reaction under inert gas protection. The reaction time was 1 hour.

[0039] Step 2, final polycondensation,

[0040] The final polycondensation reaction was carried out at 260℃ and a vacuum of 20Pa, with stirring at 50 rpm during the final polycondensation reaction; the reaction time was 6 hours.

[0041] Example 3

[0042] This embodiment discloses a third implementation of the present invention. Firstly, it discloses a high-barrier heat-shrinkable film. The technical solution adopted is a single-layer copolyester film composed of furanyl dicarboxylic acid-isosorbitol-neopentyl glycol copolyester, with the following structural formula:

[0043] .

[0044] This invention also discloses a method for preparing the above-mentioned high-barrier heat-shrinkable film, the technical solution of which includes the following steps:

[0045] Step 1, Pre-polymerization,

[0046] One part of furanyl dicarboxylic acid, one part of isosorbide, one part of TMCD, 0.1 part of tetrabutyl titanate, 0.033 parts of zinc oxide, and 0.02 parts of triphenyl phosphate were mixed and subjected to a pre-condensation reaction at 200°C under helium protection. During the reaction, stirring was applied to ensure uniform mixing of monomers and catalysts, promote heat and mass transfer and discharge of water byproduct. The stirring speed was 75 rpm, a low speed, to avoid bumping of the system and facilitate a stable reaction under inert gas protection. The reaction time was 2 hours.

[0047] Step 2, final polycondensation,

[0048] The final polycondensation reaction was carried out at 250℃ and a vacuum of 30Pa, with stirring at 35 rpm during the final polycondensation reaction; the reaction time was 4 hours.

[0049] Comparative Example 1: Chinese Patent CN109648976A;

[0050] Comparative Example 2: The single-layer structure of layer B in Chinese Patent CN109648976A;

[0051] Comparative Example 3: Traditional polyester heat shrink film;

[0052]

[0053] Then, Example 3 and Comparative Example 1 are further compared:

[0054]

[0055] The above comparison shows that:

[0056] Comparative Example 1, due to its use of more flexible segments and the relatively low proportion of rigid monomers despite the addition of some, suffers from insufficient "rigid support" of the molecular chains, resulting in a lower glass transition temperature. Furthermore, the thermal motion of the flexible segments intensifies with increasing temperature, leading to easy deformation and softening of the material, thus resulting in a lower long-term heat resistance temperature. Similarly, the low proportion of rigid monomers weakens intermolecular forces, resulting in large packing gaps and easy permeation of water vapor and oxygen. The copolymerization of flexible and rigid monomers disrupts the regularity of the molecular chains, causing the amorphous regions to become loose and further reducing the packing density. Comparative Example 1, constructed from stacked materials, exhibits poor compatibility between different layers, with tiny gaps at the interfaces providing shortcuts for small molecule penetration, further reducing overall barrier properties. Comparative Example 1, with terephthalic acid as the main dicarboxylic acid, exhibits high molecular chain regularity and a crystallinity of 10%–20%. Furthermore, the outer modified PPS layer contains numerous rigid benzene rings and thioether bonds (-Ar-S-Ar-), resulting in even higher crystallinity (>30%). The rigid chain segments are difficult to slip, leading to the elongation at break of the composite film being limited by the PPS layer (typically <100%). Additionally, in the composite structure of Comparative Example 1, the molecular chain structures of the two layers differ significantly (PPS is a rigid aromatic chain, while PET is a semi-rigid aliphatic-aromatic chain), resulting in limited interfacial adhesion (i.e.,...). Even with improvements through polar groups, microscopic interface defects still exist. Under external tensile force, stress tends to concentrate at the interface, leading to interlayer delamination or localized fracture, resulting in a low overall elongation at break. Comparative Example 1 used terephthalic acid and other dicarboxylic acids as copolymers and adopted a PET+PPS composite structure. The molecular chain regularity of PET and PPS differs more, resulting in higher crystallinity (usually >10%) and more obvious light scattering, leading to low transmittance. Furthermore, the difference in refractive index between different materials causes light to be reflected at the interface, exacerbating light scattering and further reducing transmittance.

[0057] In Example 3, the main chain uses furanyl dicarboxylic acid. The furan ring has a stronger rigid structure and lower symmetry, which can more effectively improve the crystallization resistance, molecular packing density, and intermolecular forces of the material. Furthermore, the strong polarity and steric hindrance of the furan ring can achieve a higher barrier effect, fundamentally optimizing barrier properties and heat resistance. By copolymerizing the more rigid furan ring with a rigid diol, a double rigid structure is formed, which increases the glass transition temperature, strengthens the molecular chain rigidity, improves dimensional stability at high temperatures, enhances high-temperature resistance, and increases elongation at break. Through the double rigid structure of "furan ring + cyclic diol", the symmetry and regularity of the molecular chain are significantly disrupted. This irregular structure greatly reduces the crystallization tendency of the molecular chain (crystallinity <5%). Crystallization causes light scattering at the interface between crystalline and amorphous regions. Combined with the single material, this reduces light transmittance. The higher proportion of amorphous regions (>95%) can obtain more disordered molecular chains, which can achieve a greater degree of extension through chain segment rotation and slip under external force, thus exhibiting a high elongation at break.

[0058] Furthermore, since Example 3 uses a single-layer copolyester film with a single composition, it can be directly recycled using a single treatment method of chemical depolymerization or physical remodeling, which is simple and low-cost.

[0059] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-barrier heat-shrinkable film, characterized in that, It is a single-layer copolyester film, which is obtained by copolymerizing furan dicarboxylic acid or its derivatives with rigid diols, at least one of which is a cyclic diol.

2. The high-barrier heat-shrinkable film according to claim 1, characterized in that: The copolyester component has one of the following structures: Furan dicarboxylic acid or its derivatives-neopentyl glycol-TMCD copolyester: ； Furan dicarboxylic acid or its derivatives - isosorbide - TMCD copolyester: ； Furan dicarboxylic acid or its derivatives - isosorbide-neopentyl glycol copolyester: 。 3. A method for preparing the high-barrier heat-shrinkable film as described in claim 1, characterized in that, Includes the following steps: Step 1: Mix furanyl dicarboxylic acid or its derivatives with a rigid diol, and add a catalyst and stabilizer to carry out a pre-condensation reaction; Step 2: Perform the final polycondensation reaction.

4. The method according to claim 3, characterized in that: The catalyst is a tetrabutyl titanate-zinc oxide composite catalyst, and the stabilizer is triphenyl phosphate.

5. The method according to claim 3, characterized in that: In step 1, the reaction temperature of the pre-condensation reaction is 180-220℃, and the reaction environment is protected by an inert gas.

6. The method according to claim 3, characterized in that: In step 2, the reaction temperature of the final polycondensation reaction is 240-260℃, and the vacuum degree is below 50Pa.

7. The method according to claim 3, characterized in that: The rigid diol is one or more of isosorbide, TMCD, and neopentyl glycol.

8. The method according to claim 7, characterized in that, The mass parts of diol, furanyl dicarboxylic acid or its derivatives, catalyst, and stabilizer are as follows: 1.2-3 parts rigid diol, 1 part furanyl dicarboxylic acid or its derivative, 0.1-0.2 parts catalyst, and 0.015-0.025 parts stabilizer.

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