Dental diaphragm capable of resisting stress relaxation as well as preparation method and application of dental diaphragm

Abstract

The invention provides a dental diaphragm with stress relaxation resistance as well as a preparation method and application thereof, and relates to the technical field of orthodontic materials. The dental diaphragm resistant to stress relaxation comprises a branched modified copolyester diaphragm, wherein the branched modified copolyester film is prepared from the following raw materials: terephthalic acid, alicyclic structure dihydric alcohol, side group dihydric alcohol and a polyfunctional group branching agent; wherein the glass transition temperature of the branched modified copolyester film is more than or equal to 80 DEG C, the light transmittance of the branched modified copolyester film is more than or equal to 86%, and the 24-hour tension attenuation rate of the branched modified copolyester film is less than or equal to 20%. The dental diaphragm provided by the invention has excellent tensile attenuation resistance, heat resistance and optical performance, is simple in processing technology, is more suitable for clinical requirements of dental orthodontic correction, and is particularly suitable for preparing dental orthodontic correction devices.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of dental orthodontic materials, and in particular to a stress relaxation resistant dental film and a preparation method and application thereof. BACKGROUND

[0002] With the rapid upgrading of oral health consumption, the bracket-free invisible orthodontic appliance has gradually replaced the traditional metal bracket scheme and become the fastest growing segment of the orthodontic market due to its advantages of beauty, removable wearing and digital design. The existing large-scale process generally adopts the route of “3D printing dental model-high light transmission thermoplastic polymer film hot pressing-machining”, and the optical performance, mechanical strength, heat resistance and biocompatibility of the film material directly determine the clinical expression efficiency and wearing comfort of the appliance, thus becoming the focus of competition in the industry chain technology.

[0003] The early commercialized film mainly uses a hard thermoplastic polyurethane (TPU) system, which has the characteristics of high initial modulus and good resilience, but is prone to hydrolysis yellowing, light transmission rate reduction (≤80%) and potential monomer precipitation in the oral environment, and the biological safety is controversial.

[0004] Subsequently, the mainstream scheme in the industry shifts to alcohol-modified polyethylene terephthalate glycol (PETG) copolyester, which can improve the light transmission rate to more than 85%, but the glass transition temperature and heat distortion temperature of PETG are low, which can easily induce stress cracking in hot pressing and daily cold and hot cycles; at the same time, the elongation at break is low, and the toughness reserve is limited, and a large number of tearing failure cases along the force concentration area in the clinic have occurred. Obviously, the PETG material (polyethylene terephthalate-1,4-cyclohexane dimethanol, ethylene glycol derivative structural unit content > 50 mol%) has a high elastic modulus and a significant tensile decay characteristic in orthodontic treatment, which leads to insufficient maintenance of the orthodontic force and directly affects the correction effect, and this defect has been widely pointed out in clinical application.

[0005] More importantly, both the TPU and PETG systems mentioned above exhibit significant tensile decay behavior at 37°C physiological environment, for example, the maintenance force decay rate of a 0.75 mm thick film can reach 45~80% within 21 days, which leads to insufficient orthodontic force persistence, and the actual displacement of the teeth is lower than the digital preset, and the treatment period is forced to be extended.

[0006] Although the industry attempts to alleviate the relaxation by thickening, multi-layer compounding or adding inorganic fillers, etc., it brings new problems of increased film rigidity, wearing discomfort and decreased transparency, and there is still no mature material solution that takes into account “high transparency-high toughness-anti-tensile decay”.

[0007] Therefore, developing a new type of high-molecular dental film with low tensile decay rate, excellent tear resistance and high light transmittance under the oral temperature field has become a key technical bottleneck to improve the clinical efficiency of the clear aligner.

[0008] In view of this, the present application is proposed. SUMMARY

[0009] The purpose of the present application is to provide a stress relaxation resistant dental film and its preparation method and application. The synergistic effect of the multiple components of the stress relaxation resistant dental film significantly improves the comprehensive performance of the material, including thermal stability, mechanical strength and tensile decay resistance, so that it can maintain stable mechanical performance in the complex oral environment for a long time.

[0010] In order to achieve the above-mentioned purpose of the present application, the following technical solutions are adopted: In a first aspect, the present application provides a stress relaxation resistant dental film, which comprises a branched modified copolyester film; Wherein, the preparation raw materials of the branched modified copolyester film include terephthalic acid, aliphatic cyclic diol, side group diol and multi-functional branching agent. Wherein, the glass transition temperature of the branched modified copolyester film is ≥ 80℃, the light transmittance of the branched modified copolyester film is ≥ 86%, and the 24 h tensile decay rate of the branched modified copolyester film is ≤ 20%.

[0011] Further, the 24 h tensile decay rate of the branched modified copolyester film is 5-20%.

[0012] Further, the glass transition temperature of the branched modified copolyester film is 85-120℃.

[0013] Further, the heat distortion temperature of the branched modified copolyester film is 70-105℃.

[0014] Further, the light transmittance of the branched modified copolyester film is 88-92%.

[0015] Further, the haze of the branched modified copolyester film is ≤ 1.7%.

[0016] Further, the thickness of the branched modified copolyester film is 0.3-2.0 mm.

[0017] Further, the form of the stress relaxation resistant dental film includes any one of roll material, round sheet or square sheet.

[0018] Furthermore, when the stress-relaxation-resistant dental diaphragm is a dental diaphragm roll, the width of the stress-relaxation-resistant dental diaphragm ranges from 100 to 150 mm, preferably from 120 to 140 mm, and more preferably from 137 mm.

[0019] Furthermore, when the stress-relaxation-resistant dental diaphragm is a dental diaphragm disc, the diameter of the stress-relaxation-resistant dental diaphragm ranges from 100 to 150 mm, preferably from 120 to 140 mm, and more preferably from 125 mm.

[0020] Furthermore, when the stress-relaxation-resistant dental membrane is a square dental membrane, the side length of the stress-relaxation-resistant dental membrane ranges from 100 to 150 mm, preferably from 120 to 140 mm, and more preferably from 125 mm.

[0021] Furthermore, based on the molar amount of terephthalic acid in the raw materials for preparing the branched modified copolyester film being 100 mol%, the molar content of the alicyclic diol is 60-85 mol%, and the content of the side-chain diol is 15-50 mol%.

[0022] Furthermore, the alicyclic diol is selected from any one or a combination of at least two of the following structural formulas I-1 to I-3: , , ; A1, A2, A3, A4, and A5 are each independently selected from C3-C8 cycloalkyl and C6-C15 bicycloalkyl; R1, R2, R3, R4, R5, and R6 are each independently selected from H and C1-C6 straight-chain or branched alkyl groups; L1 is selected from single-bonded and C1-C6 straight-chain or branched alkylene groups.

[0023] Furthermore, the side-chain diol is selected from any one or a combination of at least two of the compounds shown in Formula II:

[0024] Wherein, the side groups R1, R2, R3, and R4 are each independently selected from H, C1~C6 straight-chain or branched alkyl groups, and the side groups R1, R2, R3, and R4 are not all H at the same time; m is an integer between 0 and 6, n is an integer between 0 and 6, and m and n are not both 0 at the same time.

[0025] Furthermore, in the raw materials for preparing the branched modified copolyester film, the content of the multifunctional branching agent is 500~3000 ppm relative to the mass of terephthalic acid.

[0026] Furthermore, the multifunctional branching agent is selected from any one or a combination of at least two of the following: compounds containing at least two anhydride groups, compounds containing at least three hydroxyl groups, compounds containing at least three carboxyl groups, and compounds containing at least three epoxy groups.

[0027] Furthermore, the raw materials for preparing the branched modified copolyester film also include a catalyst; wherein the catalyst is a titanium-based bimetallic catalyst, and the titanium-based bimetallic catalyst includes: titanium and aluminum metal centers, and organic ligands located at the metal centers through carboxyl groups and / or hydroxyl groups.

[0028] Furthermore, the content of the catalyst is 10 to 200 ppm relative to the mass of terephthalic acid.

[0029] Furthermore, in the titanium-based bimetallic catalyst, the molar ratio of aluminum to titanium is (1~3):1.

[0030] Furthermore, the structural formula of the organic ligand is shown in Formula III below:

[0031] Among them, R1, R2, R3, and R4 are each independently selected from hydrogen, carboxyl, and hydroxyl groups, and R1, R2, R3, and R4 are not all hydrogen at the same time; a is an integer between 1 and 3, b is an integer between 0 and 3, and c is an integer between 1 and 3.

[0032] In a second aspect, the present invention provides a method for preparing a stress-relaxation resistant dental membrane as described in the first aspect, the method comprising: (1) Terephthalic acid, alicyclic diol, side-chain diol, multifunctional branching agent and catalyst are mixed and then subjected to esterification and polycondensation reactions in sequence to obtain branched modified copolyester melt. (2) The branched modified copolyester melt is filtered, cooled and solidified, and then granulated to obtain branched modified copolyester chips. (3) The branched modified copolyester chips are dried, melt-extruded and calendered in sequence to obtain the dental film resistant to stress relaxation.

[0033] Further, in step (1), the temperature of the esterification reaction is 250~270℃; the pressure of the esterification reaction is 50~200 kPa gauge pressure; and the time of the esterification reaction is 3~5 h.

[0034] Further, in step (1), the polycondensation reaction includes a pre-polycondensation reaction and a final polycondensation reaction carried out sequentially; The temperature of the prepolymerization reaction is 260~290℃; the pressure of the prepolymerization reaction is 1000~3000 Pa absolute; and the time of the prepolymerization reaction is 1~2 h. The temperature of the final polycondensation reaction is 270~300℃; the pressure of the final polycondensation reaction is 50~200Pa absolute; and the time of the final polycondensation reaction is 2~4 h.

[0035] Further, in step (2), the filtration includes: filtering the branched modified copolyester melt through a filter with a precision of 10~25μm.

[0036] Furthermore, in step (2), the cooling and curing method is water-cooled curing, and the water temperature is controlled at 20~35℃.

[0037] Furthermore, in step (2), the size of the branched modified copolyester chips obtained by pelletizing is 1~4 mm.

[0038] Furthermore, in step (3), the drying is carried out using a vacuum dehumidification dryer, the drying temperature is 65~80℃, and the drying time is 4~6 h.

[0039] Furthermore, in step (3), the melt extrusion is performed using a single-screw extruder with a screw speed of 10~30 r / min and a processing temperature of 200~250℃.

[0040] Furthermore, in step (3), the parameters of the calendering process include: the temperature of the cooling roller is 25~100℃, the linear speed is 0.5~3 m / min, which matches the extrusion speed and controls the uniformity of the film thickness.

[0041] Thirdly, the present invention provides the use of the stress-relaxation resistant dental membrane as described in the first aspect in the preparation of products for invisible orthodontic treatment.

[0042] Furthermore, the product for invisible orthodontic treatment includes dental orthodontic appliances.

[0043] Furthermore, the product used for invisible orthodontic treatment is a transparent dental orthodontic appliance.

[0044] Fourthly, the present invention provides a dental orthodontic appliance, the dental orthodontic appliance comprising a stress-relaxation resistant dental membrane as described in the first aspect, or a stress-relaxation resistant dental membrane prepared by the preparation method described in the second aspect.

[0045] Furthermore, the dental orthodontic appliance is a transparent dental orthodontic appliance.

[0046] Compared with the prior art, the present invention has the following beneficial effects: (1) The dental membrane of the present invention utilizes a three-component molecular design with synergistic effects of a multifunctional branching agent, alicyclic diol and side-chain diol: the copolymerization of alicyclic diol and side-chain diol can regulate the modulus of the copolyester sheet and inhibit molecular chain crystallization, thereby avoiding brittle fracture and ensuring the transparency of the polyester sheet. (2) By introducing a multifunctional branching agent into the dental membrane of the present invention, a uniformly dispersed topological branching network can be constructed in the main chain. It can also be used in conjunction with other diol copolymerization to drive the impact stress to be efficiently dispersed at the molecular scale. The resulting branched structure can inhibit molecular chain slippage, thereby reducing tensile attenuation. (3) In terms of the preparation process, the dental membrane of the present invention adopts a biocompatible titanium-based catalytic system and controls the amount of catalyst at an extremely low level, which fully complies with the safety standards of medical devices. Moreover, through the precise optimization of catalytic parameters and copolymerization ratio, the resulting material is superior to the orthodontic material prepared by the traditional blending process in terms of optical performance and mechanical strength. This innovation not only enriches the selection of orthodontic materials, but also provides a new solution for improving the performance of invisible orthodontic appliances. Detailed Implementation

[0047] Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.

[0048] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. 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.

[0049] In a first aspect, the present invention provides a dental membrane resistant to stress relaxation, the dental membrane resistant to stress relaxation comprising a branched modified copolyester membrane; The raw materials for preparing the branched modified copolyester film include: terephthalic acid, alicyclic diol, side-chain diol, and multifunctional branching agent. The branched modified copolyester film has a 24-hour tensile strength attenuation rate of ≤20%.

[0050] In this invention, the dental membrane is made of branched-modified copolyester. The main body of the branched-modified copolyester molecular chain is composed of structural units derived from terephthalic acid, alicyclic diols, and side-group diols, ensuring the basic mechanical, heat-resistant, and optical properties of the dental membrane. By introducing multifunctional monomers to create a branched structure in the copolyester molecular chain, the tensile strength decay of the dental membrane is reduced, making it more suitable for the clinical needs of orthodontic treatment. Therefore, with the synergistic effect of terephthalic acid, alicyclic diols, side-group diols, and multifunctional branching agents, the dental membrane of this invention possesses excellent transparency while significantly improving its resistance to tensile strength decay. The dental membrane of this invention exhibits excellent resistance to environmental tensile strength decay, superior transparency, heat resistance, and simple processing technology, making it suitable for the fabrication of orthodontic appliances.

[0051] As an optional implementation, the glass transition temperature of the branched modified copolyester film is ≥80℃, for example, it can be 80℃, 82℃, 84℃, 85℃, 86℃, 88℃, 90℃, 92℃, 94℃, 96℃, 98℃, 100℃, 102℃, 104℃, 106℃, 108℃, 110℃, 112℃, 114℃, 115℃, 116℃, 118℃, 120℃, 122℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, etc.

[0052] In a preferred embodiment, the glass transition temperature of the branched modified copolyester film is 85~120℃.

[0053] As an optional implementation, the light transmittance of the branched modified copolyester film is ≥86%, for example, it can be 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, etc.

[0054] In a preferred embodiment, the light transmittance of the branched modified copolyester film is 88-92%.

[0055] As an optional implementation, the 24-hour tensile attenuation rate of the branched modified copolyester film is ≤20%, for example, it can be 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0%, etc.

[0056] In a preferred embodiment, the 24-hour tensile strength attenuation rate of the branched modified copolyester film is 5-20%.

[0057] As an optional implementation, the heat distortion temperature of the branched modified copolyester film is 70~105℃, for example, it can be 70℃, 72℃, 74℃, 75℃, 76℃, 78℃, 80℃, 82℃, 84℃, 85℃, 86℃, 88℃, 90℃, 92℃, 94℃, 95℃, 96℃, 98℃, 100℃, 102℃, 104℃, 105℃, etc.

[0058] As an optional implementation, the haze of the branched modified copolyester film is ≤1.7%, for example, it can be 1.7%, 1.6%, 1.5%, 1.4%, 1.3%, 1.2%, 1.1%, 1.0%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, etc.

[0059] As an optional implementation, the thickness of the branched modified copolyester film is 0.3~2.0 mm, for example, it can be 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, etc.

[0060] As an optional implementation, the stress-relaxation resistant dental membrane may be in the form of any one of rolls, discs, or squares.

[0061] As an optional implementation, the circular or square pieces are cut from rolls of material.

[0062] As an optional implementation, when the stress-relaxation-resistant dental diaphragm is a dental diaphragm roll, the width of the stress-relaxation-resistant dental diaphragm is in the range of 100~150 mm, for example, it can be 100 mm, 105 mm, 110 mm, 115 mm, 120 mm, 125 mm, 130 mm, 135 mm, 140 mm, 145 mm, 150 mm, etc.

[0063] In a preferred embodiment, when the stress-relaxation resistant dental diaphragm is a dental diaphragm roll, the width of the stress-relaxation resistant dental diaphragm ranges from 120 to 140 mm.

[0064] As a more preferred embodiment, when the stress-relaxation resistant dental diaphragm is a dental diaphragm roll, the width of the stress-relaxation resistant dental diaphragm is more preferably 137 mm.

[0065] As an optional implementation, when the stress-relaxation-resistant dental membrane is a dental membrane disc, the diameter of the stress-relaxation-resistant dental membrane ranges from 100 to 150 mm, for example, it can be 100 mm, 105 mm, 110 mm, 115 mm, 120 mm, 125 mm, 130 mm, 135 mm, 140 mm, 145 mm, 150 mm, etc.

[0066] In a preferred embodiment, when the stress-relaxation-resistant dental diaphragm is a dental diaphragm disc, the diameter of the stress-relaxation-resistant dental diaphragm ranges from 120 to 140 mm.

[0067] In a more preferred embodiment, when the stress-relaxation-resistant dental diaphragm is a dental diaphragm disc, the diameter of the stress-relaxation-resistant dental diaphragm is in the range of 125 mm.

[0068] As an optional implementation, when the stress-relaxation-resistant dental membrane is a square dental membrane, the side length of the stress-relaxation-resistant dental membrane ranges from 100 to 150 mm, for example, it can be 100 mm, 105 mm, 110 mm, 115 mm, 120 mm, 125 mm, 130 mm, 135 mm, 140 mm, 145 mm, 150 mm, etc.

[0069] In a preferred embodiment, when the stress-relaxation-resistant dental membrane is a square dental membrane, the side length of the stress-relaxation-resistant dental membrane ranges from 120 to 140 mm.

[0070] In a more preferred embodiment, when the stress-relaxation-resistant dental membrane is a square dental membrane, the side length of the stress-relaxation-resistant dental membrane ranges from 125 mm.

[0071] As an optional implementation, based on a molar amount of terephthalic acid of 100 mol% in the raw materials for preparing the branched modified copolyester film, the molar content of the alicyclic diol is 60-85 mol%, for example, it can be 60 mol%, 61 mol%, 62 mol%, 63 mol%, 64 mol%, 65 mol%, 66 mol%, 67 mol%, 68 mol%, 69 mol%, 70 mol%, 71 mol%, 72 mol%, 73 mol%, 74 mol%, 75 mol%, 76 mol%, 77 mol%, 78 mol%, 79 mol%, 80 mol%, 81 mol%, 82 mol%, 83 mol%, 84 mol%, 85 mol%, etc.

[0072] As an optional implementation, based on a molar amount of terephthalic acid of 100 mol% in the raw materials for preparing the branched modified copolyester film, the content of the side-chain diol is 15-50 mol%, for example, it can be 15 mol%, 16 mol%, 17 mol%, 18 mol%, 19 mol%, 20 mol%, 21 mol%, 22 mol%, 23 mol%, 24 mol%, 25 mol%, 26 mol%, 27 mol%, 28 mol%, 29 mol%, 30 mol%, 31 mol%, 32 mol%, 33 mol%, 34 mol%, 35 mol%, 36 mol%, 37 mol%, 38 mol%, 39 mol%, 40 mol%, 45 mol%, 50 mol%, etc.

[0073] As an optional implementation, the alicyclic diol is selected from any one or a combination of at least two of the following structural formulas I-1 to I-3: , , ; A1, A2, A3, A4, and A5 are each independently selected from C3-C8 cycloalkyl and C6-C15 bicycloalkyl; R1, R2, R3, R4, R5, and R6 are each independently selected from H and C1-C6 straight-chain or branched alkyl groups; L1 is selected from single-bonded and C1-C6 straight-chain or branched alkylene groups.

[0074] As an optional implementation, the alicyclic diol is selected from any one or a combination of at least two of 1,4-cyclohexanediethanol, tricyclodecanediethanol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, hydrogenated bisphenol A, and hydrogenated biphenyl.

[0075] As an optional implementation, the side-chain diol is selected from any one or a combination of at least two of the compounds shown in Formula II:

[0076] Wherein, the side groups R1, R2, R3, and R4 are each independently selected from H, C1~C6 straight-chain or branched alkyl groups, and the side groups R1, R2, R3, and R4 are not all H at the same time; m is an integer between 0 and 6, n is an integer between 0 and 6, and m and n are not both 0 at the same time.

[0077] As an optional embodiment, the side-chain diol is selected from any one or a combination of at least two of 1,2-propanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,3-butanediol, 2,3-butanediol, and 2,2,4-trimethyl-1,3-pentanediol.

[0078] As an optional implementation, in the raw materials for preparing the branched modified copolyester film, the content of the multifunctional branching agent is 500~3000 ppm relative to the mass of terephthalic acid, for example, it can be 500 ppm, 700 ppm, 900 ppm, 1100 ppm, 1300 ppm, 1500 ppm, 1700 ppm, 1900 ppm, 2100 ppm, 2300 ppm, 2500 ppm, 2700 ppm, 2900 ppm, 3000 ppm, etc.

[0079] As an optional implementation, the multifunctional branching agent is selected from any one or a combination of at least two of the following: compounds containing at least two anhydride groups, compounds containing at least three hydroxyl groups, compounds containing at least three carboxyl groups, and compounds containing at least three epoxy groups.

[0080] As an optional embodiment, the compound containing at least two anhydride groups is selected from any one or a combination of at least two of pyromellitic dianhydride, bisphenol A type diether dianhydride, and 1,2,3,4-cyclobutanetetracarboxylic dianhydride.

[0081] As an optional implementation, the compound containing at least three hydroxyl groups is selected from any one or a combination of at least two of glycerol, pentaerythritol, dipentaerythritol, trimethylolpropane, 1,2,4-butanetriol, and sorbitol.

[0082] As an optional implementation, the compound containing at least three carboxyl groups is selected from any one or a combination of at least two of citric acid, pyromellitic acid, pyromellitic tetracarboxylic acid, and trimellitic acid.

[0083] As an optional implementation, the compound containing at least three epoxy groups is selected from any one or a combination of at least two of trimethylolpropane triglycidyl ether, glycerol triglycidyl ether, pentaerythritol triglycidyl ether, and tri(4-hydroxyphenyl)methane triglycidyl ether.

[0084] As an optional implementation, the raw materials for preparing the branched modified copolyester film also include a catalyst.

[0085] In a preferred embodiment, the catalyst is a titanium-based bimetallic catalyst, and the titanium-based bimetallic catalyst comprises: titanium and aluminum metal centers, and organic ligands located at the metal centers via carboxyl groups and / or hydroxyl groups.

[0086] As an optional implementation, the content of the catalyst is 10 to 200 ppm relative to the mass of terephthalic acid, for example, it can be 10 ppm, 20 ppm, 40 ppm, 60 ppm, 80 ppm, 100 ppm, 120 ppm, 140 ppm, 160 ppm, 180 ppm, 200 ppm, etc.

[0087] As an optional implementation, in the titanium-based bimetallic catalyst, the molar ratio of aluminum to titanium is (1~3):1, for example, it can be 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3:1, etc.

[0088] As an optional implementation, the organic ligand has the following structural formula III:

[0089] Among them, R1, R2, R3, and R4 are each independently selected from hydrogen, carboxyl, and hydroxyl groups, and R1, R2, R3, and R4 are not all hydrogen at the same time; a is an integer between 1 and 3, b is an integer between 0 and 3, and c is an integer between 1 and 3.

[0090] As an optional implementation, the organic ligand is selected from any one or a combination of at least two of 2,3-dihydroxysuccinic acid, 3-carboxy-3-hydroxyglutaric acid, and 2-hydroxysuccinic acid.

[0091] As an optional implementation, the raw materials for preparing the branched modified copolyester film also include hindered phenolic compounds.

[0092] As an optional implementation, the content of the hindered phenolic compound is 5 to 150 ppm relative to the mass of terephthalic acid, for example, it can be 5 ppm, 10 ppm, 15 ppm, 20 ppm, 25 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm, 70 ppm, 80 ppm, 90 ppm, 100 ppm, 110 ppm, 120 ppm, 130 ppm, 140 ppm, 150 ppm, etc.

[0093] As an optional embodiment, the hindered phenolic compound is selected from any one or a combination of at least two of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,6-di-tert-butyl-4-methylphenol, 2,4-dimethyl-6-(1-methylpentadecanyl)phenol, and 4,4'-methylenebis(2,6-di-tert-butylphenol).

[0094] As an optional implementation, the raw materials for preparing the branched modified copolyester film also include phosphite compounds.

[0095] As an optional implementation, the content of the phosphite compound is 20 to 200 ppm relative to the mass of terephthalic acid, for example, it can be 20 ppm, 25 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm, 70 ppm, 80 ppm, 90 ppm, 100 ppm, 110 ppm, 120 ppm, 130 ppm, 140 ppm, 150 ppm, etc.

[0096] As an optional embodiment, the phosphite compound is selected from any one or a combination of at least two of tris(2,4-di-tert-butyl)phosphite, 4,4'-biphenyl diphosphite, distearate pentaerythritol diphosphite, and bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite.

[0097] In a second aspect, the present invention provides a method for preparing a stress-relaxation resistant dental membrane as described in the first aspect, the method comprising: (1) Terephthalic acid, alicyclic diol, side-chain diol, multifunctional branching agent and catalyst are mixed and then subjected to esterification and polycondensation reactions in sequence to obtain branched modified copolyester melt. (2) The branched modified copolyester melt is filtered, cooled and solidified, and then granulated to obtain branched modified copolyester chips. (3) The branched modified copolyester chips are dried, melt-extruded and calendered in sequence to obtain the dental film resistant to stress relaxation.

[0098] As an optional implementation, in step (1), the temperature of the esterification reaction is 250~270℃, for example, it can be 250℃, 252℃, 254℃, 256℃, 258℃, 260℃, 262℃, 264℃, 266℃, 268℃, 270℃, etc.

[0099] As an optional embodiment, in step (1), the pressure of the esterification reaction is a gauge pressure of 50 to 200 kPa, for example, it can be 50 kPa, 60 kPa, 70 kPa, 80 kPa, 90 kPa, 100 kPa, 105 kPa, 110 kPa, 115 kPa, 120 kPa, 125 kPa, 130 kPa, 135 kPa, 140 kPa, 145 kPa, 150 kPa, 155 kPa, 160 kPa, 165 kPa, 170 kPa, 175 kPa, 180 kPa, 185 kPa, 190 kPa, 195 kPa, 200 kPa, etc.

[0100] As an optional implementation, in step (1), the esterification reaction time is 3 to 5 hours, for example, 3 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours, 4 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, 5 hours, etc.

[0101] As an optional implementation, in step (1), the polycondensation reaction includes a pre-polycondensation reaction and a final polycondensation reaction carried out sequentially.

[0102] As an optional implementation, in step (1), the temperature of the pre-condensation reaction is 260~290℃, for example, it can be 260℃, 262℃, 264℃, 266℃, 268℃, 270℃, 272℃, 274℃, 276℃, 278℃, 280℃, 282℃, 284℃, 286℃, 288℃, 290℃, etc.

[0103] As an optional implementation, in step (1), the pressure of the pre-condensation reaction is an absolute pressure of 1000~3000 Pa, for example, it can be 1000 Pa, 1200 Pa, 1400 Pa, 1600 Pa, 1800 Pa, 2000 Pa, 2200 Pa, 2400 Pa, 2600 Pa, 2800 Pa, 3000 Pa, etc.

[0104] As an optional implementation, in step (1), the pre-condensation reaction time is 1 to 2 hours, for example, 1 hour, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, 2 hours, etc.

[0105] As an optional implementation, in step (1), the temperature of the final polycondensation reaction is 270~300℃, for example, it can be 270℃, 272℃, 274℃, 276℃, 278℃, 280℃, 282℃, 284℃, 286℃, 288℃, 290℃, 292℃, 294℃, 296℃, 298℃, 300℃, etc.

[0106] As an optional implementation, the pressure of the final polycondensation reaction is an absolute pressure of 50~200 Pa.

[0107] As an optional implementation, in step (1), the final polycondensation reaction time is 2 to 4 hours, for example, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours, 4 hours, etc.

[0108] As an optional implementation, in step (2), the filtration includes: filtering the branched modified copolyester melt through a filter with a precision of 10~25 μm (for example, it can be 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, etc.).

[0109] As an optional implementation, in step (2), the cooling and curing method is water-cooled curing, and the water temperature is controlled at 20~35℃, for example, 20℃, 22℃, 24℃, 26℃, 28℃, 30℃, 32℃, 34℃, 35℃, etc.

[0110] As an optional implementation, in step (2), the size of the branched modified copolyester chips obtained by pelletizing is 1~4 mm, for example, it can be 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, etc.

[0111] As an optional implementation, step (2) of preparing the branched modified copolyester chips includes: filtering the copolyester melt through a filter and then sending it to the casting head for cooling and solidification, and then cutting it into pellets by a pelletizer to obtain the branched modified copolyester chips.

[0112] As an optional implementation, in step (3), the drying is performed using a vacuum dehumidification dryer.

[0113] As an optional implementation, in step (3), the drying temperature is 65~80℃, for example, it can be 65℃, 68℃, 70℃, 72℃, 75℃, 80℃, etc., and the drying time is 4~6 h, for example, it can be 4 h, 4.5 h, 5 h, 5.5 h, 6 h, etc.

[0114] As an optional implementation, in step (3), the melt extrusion is performed using a single screw extruder.

[0115] As an optional implementation, in step (3), the screw speed is 10~30 r / min, for example, it can be 10 r / min, 11 r / min, 12 r / min, 13 r / min, 14 r / min, 15 r / min, 16 r / min, 17 r / min, 18 r / min, 19 r / min, 20 r / min, 22 r / min, 24 r / min, 25 r / min, 26 r / min, 28 r / min, 30 r / min, etc., and the processing temperature is 200~250℃, for example, it can be 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, 230℃, 235℃, 240℃, 245℃, 250℃, etc.

[0116] As an optional implementation, in step (3), the parameters of the calendering process include: the temperature of the cooling roller is 25~100℃, for example, it can be 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 100℃, etc.; the linear speed is 0.5~3 m / min, which matches the extrusion speed and controls the uniformity of the film thickness.

[0117] As an optional implementation, step (3) of preparing the stress-relaxation resistant dental membrane includes: drying the branched modified copolyester chips, then melting and calendering them using a single-screw extruder, controlling the thickness of the calendered sheet to be 0.3~2.0 mm, to obtain the stress-relaxation resistant dental membrane.

[0118] Thirdly, the present invention provides the use of the stress-relaxation resistant dental membrane as described in the first aspect in the preparation of products for invisible orthodontic treatment.

[0119] As an optional implementation, the product for invisible orthodontic treatment includes dental orthodontic appliances.

[0120] As an optional implementation, the product for invisible orthodontic treatment is a transparent dental orthodontic appliance.

[0121] Fourthly, the present invention provides a dental orthodontic appliance, the dental orthodontic appliance comprising a stress-relaxation resistant dental membrane as described in the first aspect, or a stress-relaxation resistant dental membrane prepared by the preparation method described in the second aspect.

[0122] As an optional implementation, the dental orthodontic appliance is a transparent dental orthodontic appliance.

[0123]

Terminology Explanation

[0124] The term "alkyl" refers to a monovalent substituent derived from a straight-chain or branched saturated hydrocarbon; the term "C1-C6 straight-chain or branched alkyl" refers to a saturated straight-chain or branched alkyl group containing 1-6 carbon atoms, either alone or in combination, including but not limited to methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, 2-pentyl, 3-pentyl, n-hexyl, etc.

[0125] The term "alkylene" refers to a divalent substituent derived from a straight-chain or branched saturated hydrocarbon; the term "C1-C6 straight-chain or branched alkylene" refers to a saturated straight-chain or branched alkylene containing 1-6 carbon atoms, either alone or in combination, including but not limited to methylene, ethylene, n-propylene, 1,2-propylene, n-butylene, 1,3-butylene, 1,2-neopentylene, etc.

[0126] The term "cycloalkyl" refers to a substituent derived from a saturated hydrocarbon with a cyclic structure formed by carbon atoms linked by single bonds; the term "C3-C8 cycloalkyl" refers to a substituent, either alone or in combination, representing a monocyclic or polycyclic hydrocarbon containing 3 to 8 cyclic carbon atoms in the main chain, including but not limited to cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, etc.

[0127] The term "bicycloalkyl" refers to a monovalent group with unbonded electrons formed by removing a hydrogen atom from a bicycloalkane molecule (a cycloalkane in which two rings share two or more carbon atoms). The term "C6~C15 bicycloalkyl" includes, but is not limited to, bicyclo[2.2.1]heptyl, bicyclo[2.2.2]octyl, bicyclo[3.3.1]nonyl, camphenyl, pinyl, naphthyl, fenelyl, longleaf alkyl, etc.

[0128] The term "hydroxyl group" refers to -OH.

[0129] The term "carboxyl group" refers to -RCOOH, where R is H or an alkyl group, such as -COOH, -CH2COOH, etc.

[0130] The term "cycloalkyl" refers to monocyclic or polycyclic hydrocarbons derived from a main chain of 1 to 30 carbon atoms.

[0131] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0132] Example 1 This embodiment provides a stress-relaxation-resistant dental membrane and a dental orthodontic appliance containing the same. The stress-relaxation-resistant dental membrane and the dental orthodontic appliance containing the same are specifically prepared by the following steps: (1) Preparation of branched modified copolyester: (1-1) A mixture of terephthalic acid, 1,4-cyclohexanediol, 2,2-dimethyl-1,3-propanediol, and pentaerythritol is subjected to esterification under the catalysis of a titanium-based bimetallic catalyst to obtain a copolyester oligomer; wherein, based on a molar amount of terephthalic acid of 100 mol% in the raw materials for preparing the branched modified copolyester film, the molar content of 1,4-cyclohexanediol is 80 mol%, and the content of 2,2-dimethyl-1,3-propanediol is 30 mol%; the content of pentaerythritol is 1000 ppm relative to the mass of terephthalic acid; and the content of the titanium-based bimetallic catalyst, calculated as titanium element, is 50%. ppm; and in the titanium-based bimetallic catalyst, the molar ratio of aluminum to titanium is 2:1, the ligand is 2,3-dihydroxysuccinic acid, and the mass ratio of the ligand to the total mass of the bimetal is 1:7.5; wherein, the esterification reaction is carried out at a reaction temperature of 260℃, a reaction pressure of 70 kPa gauge pressure, and a reaction time of 4 h.

[0133] (1-2) The copolyester oligomer obtained in step S1 is subjected to a polycondensation reaction to obtain the branched modified copolyester melt; wherein the polycondensation reaction includes a pre-polycondensation reaction and a final polycondensation reaction; the reaction temperature of the pre-polycondensation reaction is 270°C, the reaction pressure is 2000 Pa absolute, and the reaction time is 1.5 h; the reaction temperature of the final polycondensation reaction is 280°C, the reaction pressure is 100 Pa absolute, and the reaction time is 3 h.

[0134] (2) Preparation of branched modified copolyester chips: The branched modified copolyester melt prepared in step (1) was filtered through a filter with a precision of 15 μm, flowed out through the casting head, water-cooled and solidified, and then granulated by a pelletizer to obtain branched copolyester chips with a size of about 3 mm.

[0135] (3) Preparation of dental membranes resistant to stress relaxation: After the branched copolyester chips obtained in step (2) are dried at 80°C for 4 hours, they are extruded and calendered using a single-screw extruder. The screw speed is 15 r / min, the melt extrusion temperature is 250°C, and the cooling roller temperature is 60°C. The linear speed of the cooling roller is adjusted to control the thickness of the calendered sheet to be 0.75~0.8 mm. The calendered sheet is then cut to obtain round or square copolyester films, which are the stress-relaxation-resistant dental films.

[0136] (4) Preparation of dental orthodontic appliances: The stress-relaxation resistant dental membrane obtained in step (3) is hot-pressed onto an orthodontic dental mold, and then cut, ground, polished, and disinfected to obtain a dental orthodontic appliance.

[0137] Example 2 This embodiment provides a stress-relaxation-resistant dental membrane and a dental orthodontic appliance containing the same. The stress-relaxation-resistant dental membrane and the dental orthodontic appliance containing the same are specifically prepared by the following steps: (1) Preparation of branched modified copolyester: (1-1) A mixture of terephthalic acid, 1,4-cyclohexanediol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, 2,2-dimethyl-1,3-propanediol, and trimesic acid was subjected to esterification under the catalysis of an organotitanium-aluminum bimetallic compound to obtain a copolyester oligomer; wherein, in the mixture, the amount of 1,4-cyclohexanediol added relative to the molar amount of terephthalic acid was 50 mol%, the amount of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 30 mol%, and the amount of 2-methyl-1,3-propanediol was 30 mol%; in the mixture, the amount of trimesic acid added relative to the mass of terephthalic acid was 2000 ppm, and the amount of the organotitanium-aluminum bimetallic compound added was 50 ppm based on titanium element. ppm; and in the organotitanium-aluminum bimetallic compound, the molar ratio of aluminum to titanium is 3:1, the ligand is 3-carboxy-3-hydroxyglutaric acid, and the mass ratio of the ligand to the total mass of the bimetal is 1:10; wherein, the esterification reaction is carried out at a temperature of 265°C, a pressure of 100 kPa (gauge), and a reaction time of 3 h.

[0138] (1-2) The copolyester oligomer obtained in step S1 is subjected to a polycondensation reaction to obtain the branched modified copolyester melt; wherein the polycondensation reaction includes a pre-polycondensation reaction and a final polycondensation reaction; the reaction temperature of the pre-polycondensation reaction is 270°C, the reaction pressure is 3000 Pa absolute pressure, and the reaction time is 1 h; the reaction temperature of the final polycondensation reaction is 280°C, the reaction pressure is 100 Pa absolute pressure, and the reaction time is 2.5 h.

[0139] (2) Preparation of branched modified copolyester chips: The branched modified copolyester melt prepared in step (1) was filtered through a filter with a precision of 20 μm, flowed out through the casting head, water-cooled and solidified, and then granulated by a pelletizer to obtain branched copolyester chips with a size of about 4 mm.

[0140] (3) Preparation of dental membranes resistant to stress relaxation: After the branched copolyester chips obtained in step (2) are dried at 70°C for 5 hours, they are extruded and calendered using a single-screw extruder. The screw speed is 25 r / min, the melt extrusion temperature is 245°C, and the cooling roller temperature is 55°C. The linear speed of the cooling roller is adjusted to control the thickness of the calendered sheet to be 0.75~0.8 mm. The calendered sheet is then cut to obtain round or square copolyester films, which are the stress relaxation resistant dental films.

[0141] (4) Preparation of dental orthodontic appliances: The stress-relaxation resistant dental membrane obtained in step (3) is hot-pressed onto an orthodontic dental mold, and then cut, ground, polished, and disinfected to obtain a dental orthodontic appliance.

[0142] Example 3 This embodiment provides a stress-relaxation-resistant dental membrane and a dental orthodontic appliance containing the same. The stress-relaxation-resistant dental membrane and the dental orthodontic appliance containing the same are specifically prepared by the following steps: (1) Preparation of branched modified copolyester: (1-1) A mixture of terephthalic acid, tricyclodecanediethanol, 2-butyl-2-ethyl-1,3-propanediol, and bisphenol A type diether dianhydride was subjected to esterification in the presence of a titanium bimetallic catalyst, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and tris(2,4-di-tert-butyl)phosphite to obtain a copolyester oligomer; wherein, based on a molar amount of terephthalic acid of 100 mol% in the raw materials for preparing the branched modified copolyester film, the molar content of tricyclodecanediethanol was 70 mol%, and the content of 2-butyl-2-ethyl-1,3-propanediol was 40 mol%; the content of bisphenol A type diether dianhydride was 1500 ppm relative to the mass of terephthalic acid; and the content of the titanium bimetallic catalyst, calculated as titanium element, was 100 ppm. The content of the titanium-based bimetallic catalyst is 20 ppm; and in the titanium-based bimetallic catalyst, the molar ratio of aluminum to titanium is 2:1, the ligand is 3-carboxy-3-hydroxyglutaric acid, and the mass ratio of the ligand to the total mass of the bimetal is 1:10; the content of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is 20 ppm; the content of tris(2,4-di-tert-butyl)phosphite is 20 ppm; wherein, the reaction temperature of the esterification reaction is 255℃, the reaction pressure is 100 kPa gauge pressure, and the reaction time is 3 h.

[0143] (1-2) The copolyester oligomer obtained in step S1 is subjected to a polycondensation reaction to obtain the branched modified copolyester melt; wherein the polycondensation reaction includes a pre-polycondensation reaction and a final polycondensation reaction; the reaction temperature of the pre-polycondensation reaction is 280°C, the reaction pressure is 2000 Pa absolute pressure, and the reaction time is 1 h; the reaction temperature of the final polycondensation reaction is 290°C, the reaction pressure is 80 Pa absolute pressure, and the reaction time is 2 h.

[0144] (2) Preparation of branched modified copolyester chips: Same as in Example 1.

[0145] (3) Preparation of dental membranes resistant to stress relaxation: Same as in Example 1.

[0146] (4) Preparation of dental orthodontic appliances: Same as in Example 1.

[0147] Example 4 This embodiment provides a stress-relaxation-resistant dental membrane and a dental orthodontic appliance containing the same. The stress-relaxation-resistant dental membrane and the dental orthodontic appliance containing the same are specifically prepared by the following steps: (1) Preparation of branched modified copolyester: (1-1) A mixture of terephthalic acid, hydrogenated bisphenol A, 2,3-butanediol, and pyromellitic acid was subjected to esterification in the presence of a titanium-based bimetallic catalyst, 2,4-dimethyl-6-(1-methylpentadecanyl)phenol, and 4,4'-biphenyl diphosphite to obtain a copolyester oligomer; wherein, based on a molar amount of terephthalic acid of 100 mol% in the raw materials for preparing the branched modified copolyester film, the molar content of hydrogenated bisphenol A was 85 mol%, and the content of 2,3-butanediol was 25 mol%; the content of pyromellitic acid relative to the mass of terephthalic acid was 1000 ppm; and the content of the titanium-based bimetallic catalyst, calculated as titanium element, was 200 ppm. The content of 2,4-dimethyl-6-(1-methylpentadecanyl)phenol is 50 ppm; the content of 4,4'-biphenyl diphosphite is 50 ppm; the esterification reaction is carried out at a reaction temperature of 255°C, a reaction pressure of 100 kPa gauge pressure, and a reaction time of 4 h.

[0148] (1-2) The copolyester oligomer obtained in step S1 is subjected to a polycondensation reaction to obtain the branched modified copolyester melt; wherein the polycondensation reaction includes a pre-polycondensation reaction and a final polycondensation reaction; the reaction temperature of the pre-polycondensation reaction is 280°C, the reaction pressure is 2000 Pa absolute pressure, and the reaction time is 2.5 h; the reaction temperature of the final polycondensation reaction is 290°C, the reaction pressure is 80 Pa absolute pressure, and the reaction time is 3.5 h.

[0149] (2) Preparation of branched modified copolyester chips: Same as in Example 1.

[0150] (3) Preparation of dental membranes resistant to stress relaxation: Same as in Example 1.

[0151] (4) Preparation of dental orthodontic appliances: Same as in Example 1.

[0152] Example 5 This embodiment provides a stress-relaxation-resistant dental membrane and a dental orthodontic appliance containing the same. The stress-relaxation-resistant dental membrane and the dental orthodontic appliance containing the same are specifically prepared by the following steps: (1) Preparation of branched modified copolyester: (1-1) A mixture of terephthalic acid, hydrogenated biphenyl, 2,2,4-trimethyl-1,3-pentanediol, and tris(4-hydroxyphenyl)methane triglycidyl ether was subjected to esterification in the presence of a titanium-based bimetallic catalyst, 4,4'-methylenebis(2,6-di-tert-butylphenol), and pentaerythritol diphosphite to obtain a copolyester oligomer; wherein, based on a molar amount of terephthalic acid of 100 mol% in the raw materials for preparing the branched modified copolyester film, the molar content of hydrogenated biphenyl was 70 mol%, and the content of 2,2,4-trimethyl-1,3-pentanediol was 40 mol%; the content of tris(4-hydroxyphenyl)methane triglycidyl ether was 2500 ppm relative to the mass of terephthalic acid; and the content of the titanium-based bimetallic catalyst, calculated as titanium element, was 50 ppm. The content of aluminum in the titanium-based bimetallic catalyst is 1:1; the ligand is 3-carboxy-3-hydroxyglutaric acid; the mass ratio of the ligand to the total mass of the bimetal is 1:10; the content of 4,4'-methylene bis(2,6-di-tert-butylphenol) is 20 ppm; the content of bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite is 30 ppm; and the reaction temperature of the esterification reaction is 255°C, the reaction pressure is 100 kPa (gauge), and the reaction time is 3.5 h.

[0153] (1-2) The copolyester oligomer obtained in step S1 is subjected to a polycondensation reaction to obtain the branched modified copolyester melt; wherein the polycondensation reaction includes a pre-polycondensation reaction and a final polycondensation reaction; the reaction temperature of the pre-polycondensation reaction is 280°C, the reaction pressure is 2000 Pa absolute pressure, and the reaction time is 1 h; the reaction temperature of the final polycondensation reaction is 290°C, the reaction pressure is 80 Pa absolute pressure, and the reaction time is 2 h.

[0154] (2) Preparation of branched modified copolyester chips: Same as in Example 1.

[0155] (3) Preparation of dental membranes resistant to stress relaxation: Same as in Example 1.

[0156] (4) Preparation of dental orthodontic appliances: Same as in Example 1.

[0157] Example 6 This embodiment provides a dental membrane resistant to stress relaxation. The only difference from Embodiment 1 is that, in step (1-1), based on the molar amount of terephthalic acid in the raw materials for preparing the branched modified copolyester membrane being 100 mol%, the molar content of 1,4-cyclohexanediol is 100 mol%, and the content of 2,2-dimethyl-1,3-propanediol is 10 mol%; the other steps are the same as in Embodiment 1.

[0158] Example 7 This embodiment provides a dental membrane resistant to stress relaxation. The only difference from Embodiment 1 is that, in step (1-1), based on the molar amount of terephthalic acid in the raw materials for preparing the branched modified copolyester membrane being 100 mol%, the molar content of 1,4-cyclohexanediol is 50 mol%, and the content of 2,2-dimethyl-1,3-propanediol is 60 mol%; the other steps are the same as in Embodiment 1.

[0159] Example 8 This embodiment provides a dental membrane resistant to stress relaxation. The only difference from Example 1 is that, in step (1-1), the content of pentaerythritol is 400 ppm relative to the mass of terephthalic acid; the other steps are the same as in Example 5.

[0160] Example 9 This embodiment provides a dental membrane resistant to stress relaxation. The only difference from Embodiment 1 is that, in step (1-1), the content of pentaerythritol is 4000 ppm relative to the mass of terephthalic acid; the other steps are the same as in Embodiment 1.

[0161] Example 10 This embodiment provides a dental membrane resistant to stress relaxation. The only difference from Embodiment 1 is that, in step (1-1), the temperature of the esterification reaction is 240°C and the pressure of the esterification reaction is 250 kPa (gauge pressure); the other steps are the same as in Embodiment 1.

[0162] Example 11 This embodiment provides a dental membrane resistant to stress relaxation. The only difference from Embodiment 1 is that, in step (1-1), the temperature of the esterification reaction is 280°C and the pressure of the esterification reaction is 40 kPa (gauge pressure); the other steps are the same as in Embodiment 1.

[0163] Example 12 This embodiment provides a dental membrane resistant to stress relaxation. The only difference from Embodiment 1 is that, in steps (1-2), the temperature of the pre-condensation reaction is 250°C and the pressure of the pre-condensation reaction is an absolute pressure of 3200 Pa; the temperature of the final condensation reaction is 310°C and the pressure of the final condensation reaction is an absolute pressure of 40 Pa; the other steps are the same as in Embodiment 1.

[0164] Example 13 This embodiment provides a dental membrane resistant to stress relaxation. The only difference from Embodiment 1 is that, in steps (1-2), the temperature of the pre-condensation reaction is 300°C and the pressure of the pre-condensation reaction is absolute 900 Pa; the temperature of the final condensation reaction is 260°C and the pressure of the final condensation reaction is absolute 300 Pa; the other steps are the same as in Embodiment 1.

[0165] Example 14 This embodiment provides a dental membrane resistant to stress relaxation. The only difference from Embodiment 5 is that in step (1-2), only one polycondensation is performed. The polycondensation temperature is 280°C, the polycondensation pressure is 1100 Pa, and the total polycondensation time is 3 hours. The other steps are the same as in Embodiment 5.

[0166] Comparative Example 1 This comparative example provides a dental membrane and an orthodontic appliance comprising the same, wherein the dental membrane and the orthodontic appliance comprising the same are specifically prepared by the following steps: (1) Preparation of branched modified copolyester: The only difference between this preparation and the branched modified copolyester in Example 1 is the preparation of the raw materials. Specifically, terephthalic acid, 1,4-cyclohexanediethanol and ethylene glycol are added to the reactor in a molar ratio of 1:0.35:0.85 to prepare a slurry. The slurry preparation time is 1 h and the temperature is 90°C. The catalyst preparation, esterification reaction and polycondensation reaction conditions and granulation process are the same as step (1) in Example 1.

[0167] (2) Preparation of copolyester chips: Same as in Example 1.

[0168] (3) Preparation of dental membrane: Same as in Example 1.

[0169] (4) Preparation of dental orthodontic appliances: Same as in Example 1.

[0170] Comparative Example 2 This comparative example provides a dental membrane and an orthodontic appliance comprising the same, wherein the dental membrane and the orthodontic appliance comprising the same are specifically prepared by the following steps: (1) Preparation of branched modified copolyester: The only difference between this preparation and the branched modified copolyester in Example 1 is the preparation of the raw materials. Specifically, terephthalic acid, 1,4-cyclohexanediethanol and ethylene glycol are added to the reactor in a molar ratio of 1:0.5:0.7 to prepare a slurry. The slurry preparation time is 1 h and the temperature is 90°C. The catalyst preparation, esterification reaction and polycondensation reaction conditions and granulation process are the same as step (1) in Example 1.

[0171] (2) Preparation of copolyester chips: Same as in Example 1.

[0172] (3) Preparation of dental membrane: Same as in Example 1.

[0173] (4) Preparation of dental orthodontic appliances: Same as in Example 1.

[0174] Test Example 1 Test samples: dental membranes resistant to stress relaxation provided in Examples 1-14, and copolyesters provided in Comparative Examples 1-2.

[0175] Test items: (1) Glass transition temperature (°C), test method: The copolyester was accurately weighed and placed in an aluminum crucible. The glass transition temperature was tested using a PerkinElmer DSC 8000 differential scanning calorimeter under the conditions of a heating and cooling rate of 20°C / min and a nitrogen flow rate of 50 mL / min.

[0176] (2) Heat distortion temperature: in accordance with standard GB / T1634.2 The testing was conducted according to the methods specified in 2019.

[0177] (3) Tensile modulus: Tested according to the method specified in standard GB / T 1040.1-2018.

[0178] (4) Light transmittance: in accordance with standard GB / T2410 The test shall be conducted in accordance with the methods specified in 2008.

[0179] (5) Haze: in accordance with standard GB / T2410 The test shall be conducted in accordance with the methods specified in 2008.

[0180] (6) Tensile attenuation performance, test method: The test equipment for tensile attenuation performance is Shimadzu universal testing machine. Dumbbell-shaped specimens are cut from the extruded film, the specimens are fixed on the fixture, and a tensile force is applied to the specimens to slowly stretch them to a tensile displacement of 0.5 mm. The tensile force F1 is recorded. The displacement is kept constant, and the tensile force F2 is recorded after 24 h. The tensile attenuation Fs is calculated according to the following formula.

[0181] Fs = (F1 - F2) / F1 × 100% In the formula: Fs — Tensile attenuation; F1 — Initial tension value, in Newtons (N).

[0182] F2 — Tension value after 24 hours, in Newtons (N).

[0183] The specific test results are shown in Table 1 below: Table 1

[0184] As shown in Table 1, the tensile strength attenuation of the embodiments is less than that of commercially available linear PETG copolyester and PCTG copolyester. The dental membrane has the following characteristics: tensile strength attenuation of less than 20% after 24 hours, light transmittance of more than 86%, haze of less than 1.7%, and glass transition temperature of more than 85°C. The dental membrane of the present invention possesses excellent tensile strength attenuation performance, superior transparency and heat resistance, and is simple to process, making it suitable for the preparation of dental orthodontic appliances. These test results indicate that the copolyester prepared in the embodiments can provide more suitable and stable orthodontic force in dental appliance applications, thereby achieving better treatment results.

[0185] In summary, the present invention utilizes a specific copolyester to obtain a dental orthodontic material with excellent transparency, good heat resistance, and high tensile strength attenuation. The processing technology is simple and it is suitable for preparing dental orthodontic appliances such as invisible dental orthodontic appliances.

[0186] The dental membrane is made of branched modified copolyester. The main body of the branched modified copolyester molecular chain is composed of structural units derived from terephthalic acid, alicyclic diols, and side-chain diols, which ensures the basic mechanical properties, heat resistance, and optical properties of the dental membrane. By introducing multifunctional monomers to generate a branched structure in the copolyester molecular chain, the tensile strength attenuation of the dental membrane is reduced, making it more suitable for the clinical needs of orthodontic treatment.

[0187] In summary, the present invention utilizes a specific copolyester to obtain a dental orthodontic material with excellent transparency, good heat resistance, and high tensile strength attenuation. The processing technology is simple and it is suitable for preparing dental orthodontic appliances such as invisible dental orthodontic appliances.

[0188] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A dental membrane resistant to stress relaxation, characterized in that, The stress-relaxation resistant dental membrane includes a branched-modified copolyester membrane. The raw materials for preparing the branched modified copolyester film include: terephthalic acid, alicyclic diol, side-chain diol, and multifunctional branching agent. The branched modified copolyester film has a glass transition temperature ≥80℃, a light transmittance ≥86%, and a 24-hour tensile attenuation rate ≤20%.

2. The dental membrane for resisting stress relaxation according to claim 1, characterized in that, The branched modified copolyester film exhibits a 24-hour tensile strength attenuation rate of 5-20%. Preferably, the glass transition temperature of the branched modified copolyester film is 85~120℃; Preferably, the heat distortion temperature of the branched modified copolyester film is 70~105℃; Preferably, the light transmittance of the branched modified copolyester film is 88-92%; Preferably, the haze of the branched modified copolyester film is ≤1.7%; Preferably, the thickness of the branched modified copolyester film is 0.3~2.0 mm; Preferably, the form of the stress-relaxation resistant dental membrane includes any one of roll material, round sheet, or square sheet; Preferably, when the stress-relaxation-resistant dental diaphragm is a dental diaphragm roll, the width of the stress-relaxation-resistant dental diaphragm is in the range of 100~150 mm, preferably 120~140 mm, and more preferably 137 mm. Preferably, when the stress-relaxation-resistant dental membrane is a dental membrane disc, the diameter of the stress-relaxation-resistant dental membrane is in the range of 100~150 mm, preferably 120~140 mm, and more preferably 125 mm. Preferably, when the stress-relaxation-resistant dental membrane is a square dental membrane, the side length of the stress-relaxation-resistant dental membrane is in the range of 100~150 mm, preferably 120~140 mm, and more preferably 125 mm.

3. The dental membrane for resisting stress relaxation according to claim 1, characterized in that, Based on the raw materials for preparing the branched modified copolyester film, with a molar amount of terephthalic acid of 100 mol%, the molar content of alicyclic diols is 60-85 mol%, and the content of side-chain diols is 15-50 mol%. Preferably, the alicyclic diol is selected from any one or a combination of at least two of the following structural formulas I-1 to I-3: 、 、 ； Among them, A1, A2, A3, A4, and A5 are each independently selected from C3-C8 cycloalkyl and C6-C15 bicycloalkyl; R1, R2, R3, R4, R5, and R6 are each independently selected from H and C1-C6 straight-chain or branched alkyl; L1 is selected from single-bonded and C1-C6 straight-chain or branched alkylene. Preferably, the side-chain diol is selected from any one or a combination of at least two of the compounds shown in Formula II: Wherein, the side groups R1, R2, R3, and R4 are each independently selected from H, C1~C6 straight-chain or branched alkyl groups, and the side groups R1, R2, R3, and R4 are not all H at the same time; m is an integer between 0 and 6, n is an integer between 0 and 6, and m and n are not both 0 at the same time.

4. The dental membrane resistant to stress relaxation according to claim 1, characterized in that, In the raw materials for preparing the branched modified copolyester film, the content of the multifunctional branching agent is 500~3000 ppm relative to the mass of terephthalic acid. Preferably, the multifunctional branching agent is selected from any one or a combination of at least two of the following: compounds containing at least two anhydride groups, compounds containing at least three hydroxyl groups, compounds containing at least three carboxyl groups, and compounds containing at least three epoxy groups. Preferably, the raw materials for preparing the branched modified copolyester film further include a catalyst; wherein the catalyst is a titanium-based bimetallic catalyst, and the titanium-based bimetallic catalyst includes: titanium and aluminum metal centers, and organic ligands located at the metal centers via carboxyl groups and / or hydroxyl groups; Preferably, the content of the catalyst is 10-200 ppm relative to the mass of terephthalic acid; Preferably, in the titanium-based bimetallic catalyst, the molar ratio of aluminum to titanium is (1~3):1; Preferably, the organic ligand has the following structural formula III: Among them, R1, R2, R3, and R4 are each independently selected from hydrogen, carboxyl, and hydroxyl groups, and R1, R2, R3, and R4 are not all hydrogen at the same time; a is an integer between 1 and 3, b is an integer between 0 and 3, and c is an integer between 1 and 3.

5. A method for preparing a stress-relaxation resistant dental membrane according to any one of claims 1 to 4, characterized in that, The method for preparing the stress-relaxation resistant dental membrane includes: (1) Terephthalic acid, alicyclic diol, side-chain diol, multifunctional branching agent and catalyst are mixed and then subjected to esterification and polycondensation reactions in sequence to obtain branched modified copolyester melt. (2) The branched modified copolyester melt is filtered, cooled and solidified, and then granulated to obtain branched modified copolyester chips. (3) The branched modified copolyester chips are dried and melt extruded and calendered in sequence to obtain the dental film resistant to stress relaxation.

6. The method for preparing a stress-relaxation resistant dental membrane according to claim 5, characterized in that, In step (1), the temperature of the esterification reaction is 250~270℃; the pressure of the esterification reaction is 50~200 kPa gauge pressure; and the time of the esterification reaction is 3~5 h. Preferably, in step (1), the polycondensation reaction includes a pre-polycondensation reaction and a final polycondensation reaction performed sequentially; The temperature of the prepolymerization reaction is 260~290℃; the pressure of the prepolymerization reaction is 1000~3000Pa absolute; and the time of the prepolymerization reaction is 1~2 h. The temperature of the final polycondensation reaction is 270~300℃; the pressure of the final polycondensation reaction is absolute pressure 50~200 Pa; and the time of the final polycondensation reaction is 2~4 h.

7. The method for preparing a stress-relaxation resistant dental membrane according to claim 5, characterized in that, In step (2), the filtration includes: filtering the branched modified copolyester melt through a filter with a precision of 10~25 μm; Preferably, in step (2), the cooling and curing method is water-cooled curing, and the water temperature is controlled at 20~35℃; Preferably, in step (2), the size of the branched modified copolyester chips obtained by pelletizing is 1~4 mm.

8. The method for preparing a stress-relaxation resistant dental membrane according to claim 5, characterized in that, In step (3), the drying is carried out using a vacuum dehumidification dryer, the drying temperature is 65~80℃, and the drying time is 4~6 h; Preferably, in step (3), the melt extrusion is performed using a single-screw extruder with a screw speed of 10~30 r / min and a processing temperature of 200~250℃; Preferably, in step (3), the parameters of the calendering process include: the temperature of the cooling roller is 25~100℃, the linear speed is 0.5~3 m / min, which matches the extrusion speed and controls the uniformity of the film thickness.

9. The use of a stress-relaxation resistant dental membrane according to any one of claims 1 to 4 in the preparation of a product for invisible orthodontic treatment; Preferably, the product for invisible orthodontic treatment includes dental orthodontic appliances, and more preferably, transparent dental orthodontic appliances.

10. A dental orthodontic appliance, characterized in that, The dental orthodontic appliance includes a stress-relaxation resistant dental membrane as described in any one of claims 1 to 4, or a stress-relaxation resistant dental membrane prepared by the preparation method as described in any one of claims 5 to 8. Preferably, the dental orthodontic appliance is a transparent dental orthodontic appliance.

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