Polyester material for heat shrink film and preparation method thereof

Abstract

The invention discloses a polyester material for a heat shrink film and a preparation method thereof, and belongs to the technical field of polyester film preparation, the polyester material for the heat shrink film comprises a first polyester resin and a second polyester resin, the first polyester resin is polyethylene glycol terephthalate-neopentyl glycol ester or a mixture of polyethylene glycol terephthalate-neopentyl glycol ester and polyethylene glycol terephthalate, and the second polyester resin is prepared from terephthalyl alcohol serving as an initiator, alkali metal carboxylate serving as a catalyst, anhydride, 3, 3 ', 5'-tetramethyl-1, 3, 5-trimethyl-1, 3, 5-trimethyl-1, 3, 5-trimethyl-1, 3, 5-trimethyl-1, 3, 5-trimethyl-1, 3, 5- The catalyst is a product obtained by copolymerization of 1, 3-dimethyl oxetane and phthalate as raw materials. The polyester material for the heat shrink film is prepared by blending, can generate a shrinkage rate of 75% or above at 80 DEG C, has good wear resistance, and keeps high tensile strength and elongation at break.

Description

Technical Field

[0001] The present invention relates to the technical field of polyester film preparation, and particularly relates to a polyester material for heat shrinkable film and a preparation method thereof. Background Art

[0002] A heat shrinkable film is a film that shrinks when heated and thus tightly adheres to the surface of the packaged item. It is usually made of plastic and has good flexibility and shrinkage properties. The heat shrinkable film can protect the product, prevent dust, moisture, and scratches, and can improve the display effect and packaging aesthetics of the product. Its shrinkage principle is achieved by heating to make the polymer chain segments in the film move more intensively. In practical applications, according to different materials and properties, heat shrinkable packaging films are widely used in the packaging of many fields such as food, beverages, daily chemical products, and electronic products, especially in the packaging of irregularly shaped items or combined (bundled) products.

[0003] Existing heat shrinkable films mainly include PVC (polyvinyl chloride), PE (polyethylene), and PET (polyethylene terephthalate). PVC has good transparency and gloss, making the product appearance more attractive. Its heat shrinkage performance is outstanding, with a relatively high shrinkage rate, and it can tightly adhere to the item, providing a good packaging effect; it has good mechanical strength and can play a certain protective role for the product, but its environmental friendliness is relatively poor, and it may release harmful substances under high temperature or specific conditions; PE has excellent flexibility, strong tensile and tear resistance, and is not easy to break, suitable for packaging items with irregular shapes or sharp corners. It has high chemical stability and is resistant to corrosion by chemical substances such as acids and alkalis. The shrinkage temperature range is relatively wide, and the operation is relatively easy. After shrinkage, it can maintain good flexibility and is not easy to become brittle, but its transparency is generally not as good as that of PVC; PET has relatively high mechanical strength and rigidity, can provide reliable protection for the product, has high transparency, good chemical resistance and heat resistance, can maintain good performance at different ambient temperatures, and is non-toxic, odorless, and easy to recycle, with good environmental friendliness. In developed countries, it has become an ideal substitute for PVC heat shrinkable films. However, since ordinary polyester is a crystalline high polymer, its shrinkage at low temperatures is relatively poor. Existing technologies improve its low-temperature shrinkage by modifying monomers, such as introducing other monomers (such as neopentyl glycol, 1,4-cyclohexanedimethanol) to prepare PETG materials, but its low-temperature shrinkage still needs to be further improved. While improving the low-temperature shrinkage performance, it is also necessary to maintain its mechanical properties and wear resistance to meet the packaging requirements. Summary of the Invention

[0004] In view of the above problems, the present invention provides a polyester material for heat shrinkable film and a preparation method thereof.

[0005] The object of the present invention is achieved by the following technical solutions: A polyester material for heat-shrinkable film, the polyester material for heat-shrinkable film comprising a first polyester resin and a second polyester resin; The first polyester resin is poly(ethylene terephthalate-neopentyl glycol) or a mixture of poly(ethylene terephthalate-neopentyl glycol) and polyethylene terephthalate; The preparation method of the second polyester resin comprises the following steps: (1) Weigh terephthalyl alcohol, acid anhydride, 3,3-dimethyloxetane and phthalide respectively and mix them. Under a protective atmosphere, add an alkali metal carboxylate as a catalyst, keep stirring and reacting at 40-70 °C for 1-6 h. After the reaction is completed, cool down, add dichloromethane to dilute the reaction system, stir and dissolve, then add it to a cold methanol solvent for precipitation, filter and dry in vacuum to obtain; Among them, the acid anhydride is one or more of phthalic anhydride, biphenyl dicarboxylic anhydride, 5-norbornene-endo-2,3-dicarboxylic anhydride. In some preferred embodiments, the mass ratio of the first polyester resin to the second polyester resin in the polyester material for heat-shrinkable film is 1:(0.5-1.4).

[0006] In some preferred embodiments, the mass ratio of poly(ethylene terephthalate-neopentyl glycol) to polyethylene terephthalate in the first polyester resin is 1:(0-1.3).

[0007] In some preferred embodiments, the mass ratio of terephthalyl alcohol to the acid anhydride, 3,3-dimethyloxetane, phthalide, and the alkali metal carboxylate is (0.01-0.05):1:(2.1-2.8):(1.2-1.8):(0.01-0.05).

[0008] In some preferred embodiments, the anion in the alkali metal carboxylate is acetate ion, propionate ion, butyrate ion or valerate ion, and the cation is lithium ion, sodium ion or potassium ion.

[0009] In some preferred embodiments, the acid anhydride includes 5-norbornene-endo-2,3-dicarboxylic anhydride, and the preparation method of the second polyester resin further comprises the following steps: (2) Disperse and dissolve the polymerization product obtained in step (1) in a dichloromethane solvent. Under a protective atmosphere, add 3-phenylpropanethiol, stir and mix, then add a radical initiator, heat up to 60-80 °C, keep stirring and reacting under a protective atmosphere for 8-18 h. After the reaction is completed, cool down, and then add it to a cold methanol solvent for precipitation, filter and dry in vacuum to obtain.

[0010] In some preferred embodiments, the mass ratio of 5-norbornene-endo-2,3-dicarboxylic anhydride in the acid anhydride is 10-30%.

[0011] In some preferred embodiments, the mass ratio of the polymerization product, 3-phenylpropanethiol, and the radical initiator is 10:(1-2.4):(0.01-0.04).

[0012] In some preferred embodiments, the radical initiator is azobisisobutyronitrile, azobisisoheptonitrile, benzoyl peroxide, or tert-butyl benzoyl peroxide.

[0013] Another aspect of the present invention is to provide a method for preparing the polyester material for the heat-shrinkable film, comprising the following steps: S1. Weigh the first polyester resin in proportion and reserve it. S2. Prepare and weigh the second polyester resin in proportion and reserve it. S3. Dry the first polyester resin and the second polyester resin, mix them evenly and then co-extrude to obtain the product.

[0014] The beneficial effects of the present invention are as follows: Aiming at the problems that the low-temperature shrinkage performance of PETG or PET materials in the prior art is poor, and the mechanical properties and wear resistance are difficult to meet the packaging requirements, the present invention prepares a polyester material for a heat-shrinkable film by blending a second polyester resin on the basis of existing polyethylene terephthalate-neopentyl glycol ester and polyethylene terephthalate. The polyester material for the heat-shrinkable film can have a shrinkage rate of more than 75% at 80°C, has good wear resistance, and at the same time maintains high tensile strength and elongation at break. In the present invention, the second polyester resin uses p-xylene glycol as an initiator, an alkali metal carboxylate as a catalyst, and an acid anhydride, 3,3-dimethyloxetane, and phthalide as raw materials for copolymerization. Among them, the alkali metal carboxylate activates the acid anhydride and p-xylene glycol and reacts to open the ring to form an ester and a carboxylate ion, and the carboxylate ion then copolymerizes with oxetane to obtain a polyester. After the acid anhydride is consumed, the alkoxy at the end of the polymer chain further initiates the polymerization with phthalide to obtain the second polyester resin. By blending the second polyester resin with PETG or PET, its low-temperature shrinkage performance is effectively improved, and at the same time, its good mechanical properties and wear resistance are maintained. Further, the present invention utilizes the introduced norbornene unsaturated double bond to introduce an alkylbenzene side chain through a thiol-ene click reaction, improve the π-π stacking effect between side chains, increase the activation energy of the restricted movement of the main chain, and further improve the heat-shrinkage performance. Specific Embodiments

[0015] The present invention will be further described in conjunction with the following examples.

[0016] Example 1 A polyester material for heat-shrinkable film, the polyester material for heat-shrinkable film includes a first polyester resin and a second polyester resin, and the mass ratio of the first polyester resin to the second polyester resin is 1:0.9; The first polyester resin is a mixture of polyethylene terephthalate-neopentyl glycol ester and polyethylene terephthalate, and the mass ratio of polyethylene terephthalate-neopentyl glycol ester to polyethylene terephthalate is 1:0.7; The preparation method of the second polyester resin includes the following steps: (1) Weigh terephthalyl alcohol, acid anhydride, 3,3-dimethyloxetane (CAS No.: 6921-35-3) and phthalide (CAS No.: 87-41-2) respectively and mix them. Under a protective atmosphere, add potassium neopentanoate as a catalyst, keep stirring at 55 °C for 3 h. After the reaction is completed, cool down, add dichloromethane to dilute the reaction system, stir and dissolve, then add it to a cold methanol solvent for precipitation, filter and dry in vacuum to obtain; The acid anhydride is a mixture of phthalic anhydride, biphenyl dicarboxylic anhydride and 5-norbornene-endo-2,3-dicarboxylic anhydride, and their mass ratio is 2:1:1; The mass ratio of the terephthalyl alcohol to the acid anhydride, the 3,3-dimethyloxetane, the phthalide, and the potassium neopentanoate is 0.03:1:2.4:1.5:0.026; The preparation method of the polyester material for heat-shrinkable film includes the following steps: S1. Weigh the first polyester resin according to the proportion for standby; S2. Prepare and weigh the second polyester resin according to the proportion for standby; S3. Dry the first polyester resin and the second polyester resin until the water content is not more than 100 ppm, mix them evenly and then co-extrude to obtain.

[0017] Example 2 A polyester material for heat-shrinkable film, the polyester material for heat-shrinkable film includes a first polyester resin and a second polyester resin, and the mass ratio of the first polyester resin to the second polyester resin is 1:0.5; The first polyester resin is polyethylene terephthalate-neopentyl glycol ester; The preparation method of the second polyester resin includes the following steps: (1) Weigh terephthalyl alcohol, acid anhydride, 3,3-dimethyloxetane, and phthalide respectively and mix them. Under a protective atmosphere, add potassium pivalate as a catalyst, keep stirring at 40 °C for 2 h. After the reaction is completed, cool down, add dichloromethane to dilute the reaction system, stir to dissolve and then add it to a cold methanol solvent for precipitation. Filter and dry in vacuum to obtain it; The acid anhydride is a mixture of phthalic anhydride and diphenic anhydride, and the mass ratio is 2:1; The mass ratio of terephthalyl alcohol to the acid anhydride, 3,3-dimethyloxetane, phthalide, and potassium pivalate is 0.01:1:2.1:1.2:0.01.

[0018] The preparation method of the polyester material for the heat-shrinkable film is the same as that in Example 1.

[0019] Example 3 A polyester material for a heat-shrinkable film, the polyester material for the heat-shrinkable film includes a first polyester resin and a second polyester resin, and the mass ratio of the first polyester resin to the second polyester resin is 1:1.4; The first polyester resin is a mixture of polyethylene terephthalate-neopentyl glycol ester and polyethylene terephthalate, and the mass ratio of polyethylene terephthalate-neopentyl glycol ester to polyethylene terephthalate is 1:1.3; The preparation method of the second polyester resin includes the following steps: (1) Weigh terephthalyl alcohol, acid anhydride, 3,3-dimethyloxetane, and phthalide respectively and mix them. Under a protective atmosphere, add potassium pivalate as a catalyst, keep stirring at 70 °C for 6 h. After the reaction is completed, cool down, add dichloromethane to dilute the reaction system, stir to dissolve and then add it to a cold methanol solvent for precipitation. Filter and dry in vacuum to obtain it; The acid anhydride is a mixture of phthalic anhydride and 5-norbornene-endo-2,3-dicarboxylic anhydride, and the mass ratio is 2:1; The mass ratio of terephthalyl alcohol to the acid anhydride, 3,3-dimethyloxetane, phthalide, and potassium pivalate is 0.05:1:2.8:1.8:0.05; The preparation method of the polyester material for the heat-shrinkable film is the same as that in Example 1.

[0020] Example 4 A polyester material for a heat-shrinkable film, the polyester material for the heat-shrinkable film includes a first polyester resin and a second polyester resin, and the mass ratio of the first polyester resin to the second polyester resin is 1:0.9; The first polyester resin is a mixture of polyethylene terephthalate-neopentyl glycol ester and polyethylene terephthalate, and the mass ratio of the polyethylene terephthalate-neopentyl glycol ester to the polyethylene terephthalate is 1:0.7; The preparation method of the second polyester resin comprises the following steps: (1) Weigh terephthalyl alcohol, acid anhydride, 3,3-dimethyloxetane and phthalide respectively and mix them. Under a protective atmosphere, add potassium neopentanoate as a catalyst, keep stirring at 55 °C for 3 h. After the reaction is completed, cool down, add dichloromethane to dilute the reaction system, stir to dissolve and then add it to a cold methanol solvent for precipitation. Filter and dry in vacuum to obtain; The acid anhydride is a mixture of phthalic anhydride, biphenyl dianhydride and 5-norbornene-endo-2,3-dicarboxylic anhydride, and their mass ratio is 2:1:1; The mass ratio of the terephthalyl alcohol to the acid anhydride, the 3,3-dimethyloxetane, the phthalide and the potassium neopentanoate is 0.03:1:2.4:1.5:0.026; (2) Disperse and dissolve the polymerization product obtained in step (1) in a dichloromethane solvent. Under a protective atmosphere, add 3-phenylpropanethiol, stir and mix, then add azobisisobutyronitrile, heat up to 70 °C, keep stirring at 70 °C for 12 h under a protective atmosphere. After the reaction is completed, cool down, and then add it to a cold methanol solvent for precipitation. Filter and dry in vacuum to obtain; The mass ratio of the polymerization product to the 3-phenylpropanethiol and the azobisisobutyronitrile is 10:1.6:0.03; The preparation method of the polyester material for the heat-shrinkable film is the same as that in Example 1.

[0021] Comparative Example 1 A polyester material for a heat-shrinkable film, the polyester material for the heat-shrinkable film comprises a first polyester resin and a second polyester resin, and the mass ratio of the first polyester resin to the second polyester resin is 1:0.9; The first polyester resin is a mixture of polyethylene terephthalate-neopentyl glycol ester and polyethylene terephthalate, and the mass ratio of the polyethylene terephthalate-neopentyl glycol ester to the polyethylene terephthalate is 1:0.7; The preparation method of the second polyester resin comprises the following steps: (1) Weigh terephthalyl alcohol, acid anhydride and 3,3-dimethyloxetane respectively and mix them. Under a protective atmosphere, add potassium neopentanoate as a catalyst, keep stirring at 55 °C for 3 h. After the reaction is completed, cool down, add dichloromethane to dilute the reaction system, stir to dissolve and then add it to a cold methanol solvent for precipitation. Filter and dry in vacuum to obtain; The acid anhydride is a mixture of phthalic anhydride, biphenyl dicarboxylic anhydride and 5-norbornene-endo-2,3-dicarboxylic anhydride, and the mass ratio thereof is 2:1:1; The mass ratio of the terephthalyl alcohol to the acid anhydride, the 3,3-dimethyloxetane and the potassium pivalate is 0.03:1:2.4:0.026; The preparation method of the polyester material for the heat-shrinkable film is the same as that in Example 1.

[0022] Comparative Example 2 A polyester material for a heat-shrinkable film, wherein the polyester material for the heat-shrinkable film is a mixture of polyethylene terephthalate-neopentyl glycol ester and polyethylene terephthalate, and the mass ratio of the polyethylene terephthalate-neopentyl glycol ester to the polyethylene terephthalate is 1:0.7.

[0023] Experimental Example The property parameters of the polyester materials prepared in Examples 1-4 and Comparative Examples 1-2 or the heat-shrinkable films made therefrom were detected. Among them, the method for measuring the heat shrinkage rate was to cut the shrink film sample into 100 mm × 100 mm (±0.1 mm), soak it in warm water at 80 °C for 10 s under no load, take it out and immerse it in normal temperature water at 25 °C, and measure the transverse length of the sample after cooling. The heat shrinkage rate value was calculated as the ratio of the length difference before and after shrinkage to the length before shrinkage, and the measurement was taken three times in parallel and averaged; the detection of tensile strength and elongation at break referred to GB / T 1040.3 (ASTM D882); the detection of friction coefficient referred to GB / T 10006 (ASTM D1894); the detection of haze referred to GB / T 2410 (ASTM D1003); the detection of glossiness referred to GB / T8807; the detection results are shown in Table 1.

[0024] Table 1 Property parameters of the polyester materials or the heat-shrinkable films made therefrom in Examples 1-4 and Comparative Examples 1-2

[0025] From the detection results of Examples 1-4, it can be seen that the polyester material of the present invention has good low-temperature shrinkage rate and mechanical properties, and can meet the requirements of various packaging materials, especially suitable for container labels with a large difference in diameter between the neck and the bottle body; according to the comparison results between Example 1 and Example 4, it can be seen that the introduction of the alkylbenzene side chain has an improvement effect on both the heat shrinkage performance and the mechanical properties of the polyester material; according to the comparison results between Example 1 and Comparative Example 1, it can be seen that the introduction of phthalide has a key role in improving the heat shrinkage performance of the polyester material; according to the comparison results between Example 1 and Comparative Example 2, it can be seen that the introduction of the second polyester material effectively reduces the heat shrinkage temperature of the polyester material while maintaining the mechanical properties and friction properties.

[0026] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A polyester material for heat-shrinkable film, characterized in that, The polyester material for heat shrinkable film comprises a first polyester resin and a second polyester resin; The first polyester resin is polyethylene terephthalate-neopentyl glycol ester or a mixture of polyethylene terephthalate-neopentyl glycol ester and polyethylene terephthalate; The preparation method of the second polyester resin comprises the following steps: (1) Weigh terephthalyl alcohol, acid anhydride, 3,3-dimethyloxetane and phthalide respectively and mix them. Under a protective atmosphere, add an alkali metal carboxylate as a catalyst, keep stirring at 40 - 70 °C for 1 - 6 h, cool down after the reaction is completed, add dichloromethane to dilute the reaction system, stir and dissolve, then add it to a cold methanol solvent for precipitation, filter and dry in vacuum to obtain it; Among them, the acid anhydride is one or more of phthalic anhydride, biphenyl dicarboxylic anhydride, 5-norbornene-endo-2,3-dicarboxylic anhydride.

2. The polyester material for heat-shrinkable film according to claim 1, characterized in that, In the polyester material for heat shrinkable film, the mass ratio of the first polyester resin to the second polyester resin is 1:(0.5 - 1.4).

3. The polyester material for heat-shrinkable film according to claim 1, characterized in that, In the first polyester resin, the mass ratio of polyethylene terephthalate-neopentyl glycol ester to polyethylene terephthalate is 1:(0 - 1.3).

4. The polyester material for heat-shrinkable film according to claim 1, characterized in that, The mass ratio of terephthalyl alcohol to the acid anhydride, 3,3-dimethyloxetane, phthalide, and the alkali metal carboxylate is (0.01 - 0.05):1:(2.1 - 2.8):(1.2 - 1.8):(0.01 - 0.05).

5. The polyester material for heat-shrinkable film according to claim 1, characterized in that, The anion in the alkali metal carboxylate is acetate ion, propionate ion, butyrate ion or valerate ion, and the cation is lithium ion, sodium ion or potassium ion.

6. The polyester material for heat-shrinkable film according to claim 1, characterized in that, The acid anhydride includes 5-norbornene-endo-2,3-dicarboxylic anhydride, and the preparation method of the second polyester resin further comprises the following steps: (2) Disperse and dissolve the polymerization product obtained in step (1) in a dichloromethane solvent. Under a protective atmosphere, add 3-phenylpropanethiol, stir and mix, then add a radical initiator, heat up to 60 - 80 °C, keep stirring at 60 - 80 °C for 8 - 18 h under a protective atmosphere, cool down after the reaction is completed, then add it to a cold methanol solvent for precipitation, filter and dry in vacuum to obtain it.

7. The polyester material for heat-shrinkable film according to claim 6, characterized in that, The mass ratio of 5-norbornene-endo-2,3-dicarboxylic anhydride in the acid anhydride is 10 - 30%.

8. The polyester material for heat-shrinkable film according to claim 6, characterized in that, The mass ratio of the polymerization product to 3-phenylpropanethiol and the radical initiator is 10:(1 - 2.4):(0.01 - 0.04).

9. The polyester material for heat-shrinkable film according to claim 6, characterized in that, The radical initiator is azobisisobutyronitrile, azobisisoheptonitrile, benzoyl peroxide or tert-butyl benzoyl peroxide.

10. A preparation method of the polyester material for heat-shrinkable film according to any one of claims 1-9, characterized in that, Comprises the following steps: S1. Weigh the first polyester resin according to the proportion for standby; S2. Prepare and weigh the second polyester resin according to the proportion for standby; S3. Dry the first polyester resin and the second polyester resin, mix them evenly and then co-extrude to obtain it.

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