Epoxy resin for food packaging coating

Abstract

The invention belongs to the technical field of food packaging coatings, and discloses an epoxy resin for a food packaging coating, and the epoxy resin is prepared from the following raw materials in parts by weight: 70-90 parts of bisphenol A, 10-30 parts of hexanediol, 30-50 parts of primary bisphenol A epoxy resin relative to the total epoxy equivalent, 14-18 parts of a chain extender and 0.5-2 parts of a catalyst. Resin is synthesized through a bisphenol A type two-step epoxy synthesis process, hexanediol is used for replacing part of bisphenol A, and the hexanediol and primary bisphenol A epoxy resin are heated under the action of a catalyst to synthesize the novel epoxy resin. The 9-type bisphenol A epoxy resin has the advantages that by controlling the proportion of hexanediol, the flexibility and toughness of the resin can be obviously improved, better infiltration and filling are facilitated, the performance of coating and composite materials is improved, meanwhile, the degree of 9-type bisphenol A epoxy can be maintained through the chemical resistance of the resin by controlling the proportion of hexanediol, and the mechanical performance of the resin is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of food packaging coatings, in particular to an epoxy resin for food packaging coatings. Background Art

[0002] Tinplate is the common name for tinplate, which is a cold-rolled thin steel plate coated with an extremely thin layer of metallic tin on both sides. It is a commonly used food packaging material.

[0003] In the field of tinplate packaging, the choice of coating is crucial, especially when comparing the coating for easy-open ends with the coating for can bottom covers. Due to the high processing requirements and the consistent chemical resistance requirements of the coating and the can bottom covers, type 9 bisphenol A epoxy resin (epoxy equivalent between 2500-3500g / eq) can meet the needs of these two coatings due to its good performance.

[0004] However, there are still some challenges in some coatings with pigments and fillers (hereinafter referred to as colored paints). The addition of pigments and fillers will reduce the cross-linking density of the coating film, which results in the chemical resistance of the colored paint being lower than that of the varnish under the condition of equal processing flexibility. In order to improve the chemical resistance of the colored paint, one method is to increase the degree of curing, but this will lead to a decrease in the flexibility and processing of the coating. This decrease in flexibility is particularly obvious during the processing of easy-open lids, which may cause cracking of the coating film at the rivets and countersunk positions. Another method is to use high molecular polyester materials instead. Although this can improve the performance of the coating, it will also bring about a significant increase in cost. Therefore, this epoxy resin needs to be improved and optimized so that its flexibility is significantly improved compared to the existing Type 9, and its chemical resistance remains at the level of Type 9 epoxy, without a significant increase in cost. Summary of the invention

[0005] The object of the present invention is to provide an epoxy resin for food packaging coating to solve the problems raised in the above background technology.

[0006] In order to achieve the above object, the present invention provides the following technical solution: an epoxy resin for food packaging coating, wherein the epoxy resin is prepared from the following raw materials in weight ratio: 70-90 parts of bisphenol A, 10-30 parts of hexanediol, 30-50 parts of primary bisphenol A epoxy resin relative to the total epoxy equivalent, 14-18 parts of chain extender and 0.5-2 parts of catalyst;

[0007] The chain extender is a polyol and does not exceed 20% of bisphenol A. The catalyst is a quaternary ammonium salt catalyst, which is responsible for accelerating the reaction.

[0008] Preferably, the preparation method of the epoxy resin is:

[0009] Step 1: Pretreatment stage: prepare raw materials and reactor according to the formula ratio;

[0010] Step 2: prepolymerization reaction stage, weighed bisphenol A, chain extender and hexylene glycol are put into a reaction kettle for reaction, and a catalyst is added;

[0011] Step 3, epoxidation reaction stage, adding primary bisphenol A epoxy resin after the prepolymer reaction is completed;

[0012] Step 4: Cooling stage: After the reaction is completed, the reactor is cooled to room temperature and subjected to vacuum degassing treatment.

[0013] Preferably, the reaction process of the prepolymerization stage is:

[0014] A1, put the weighed bisphenol A, chain extender and hexylene glycol into a reactor, and ensure that the reactor is completely sealed;

[0015] A2, slowly heat the reactor to 120-180℃, while keeping stirring to ensure that the materials are evenly mixed:

[0016] A3, after reaching the required temperature of the catalyst, add the catalyst and continue heating and stirring;

[0017] A4, continue the reaction and observe the viscosity change of the material in the reactor to ensure that the reaction is fully carried out;

[0018] A5, after 2-4 hours of reaction, a prepolymer is formed.

[0019] Preferably, in the epoxy reaction stage, after adding the primary bisphenol A epoxy resin, the temperature should be continuously heated to 150-200° C. for 1-3 hours with stirring.

[0020] Preferably, during the epoxidation reaction stage, a titration method is used in the reactor to monitor the change of epoxy groups during the reaction process to ensure that the epoxy equivalent is within the range of 3500-5500 g / eq.

[0021] Preferably, the processing steps of the cooling stage are:

[0022] B1, after the reaction is completed, slowly cool the reactor to room temperature;

[0023] B2, during the cooling process, slightly heats the resin so that the internal gas can reach the resin surface faster and be extracted by the vacuum system;

[0024] B3, at this time, the epoxy resin production is completed, and the epoxy resin is tested for tensile strength, flexibility, chemical resistance and other properties to ensure that the product meets the expected standards.

[0025] Preferably, the chain extender can increase the length of the resin molecular chain, so that the molecular weight of the epoxy resin is increased, thereby improving its physical and mechanical properties and heat resistance.

[0026] Preferably, the preparation method can flexibly control the curing time by adjusting the amount of catalyst used, thereby adapting to different processing requirements.

[0027] The beneficial effects of the present invention are as follows:

[0028] 1. The present invention synthesizes the resin through a bisphenol A type two-step epoxy synthesis process, and replaces part of the bisphenol A with hexanediol, and heats it with a primary bisphenol A epoxy resin under the action of a catalyst to synthesize a new epoxy resin. Compared with traditional epoxy resins, the epoxy resin uses hexanediol as a flexible segment, which can significantly improve the flexibility and toughness of the resin, facilitate better infiltration and filling, and improve the performance of coatings and composite materials. At the same time, by controlling the proportion of hexanediol, the chemical resistance of the resin can maintain the level of 9-type bisphenol A epoxy, thereby improving the mechanical properties of the resin.

[0029] 2. The present invention adopts a two-step production process, so that the production reaction time of the resin is relatively short, the temperature fluctuation is small, and it is easy to control, which is conducive to obtaining stable product quality. At the same time, the synthesis process is consistent with type 9 epoxy, and the price of hexanediol is higher than bisphenol A, so that the epoxy resin can reduce costs and increase efficiency while ensuring mechanical properties, and has greater economic benefits. More importantly, the coating compounded with the resin can meet the processing flexibility of tinplate easy-to-open cover, and maintain chemical resistance consistent with existing coatings, thereby improving applicability.

[0030] 3. In the present invention, by adding hexanediol and chain extender in the prepolymerization reaction stage, the chain segments in the resin molecular structure are more flexible, the resin has better fluidity after being made into a coating, and the construction leveling effect is better. In addition, the polyol molecular chains are relatively long, and they can act as a bridge in the resin molecules to connect different resin molecular chains, thereby increasing the flexibility and toughness of the resin and ensuring the stability of the epoxy resin. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The present invention is a flow chart for preparing the epoxy resin. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] like Figure 1As shown, an embodiment of the present invention provides an epoxy resin for food packaging coating, wherein the epoxy resin is prepared from the following raw materials in weight ratio: 70-90 parts of bisphenol A, 10-30 parts of hexanediol, 30-50 parts of primary bisphenol A epoxy resin relative to the total epoxy equivalent, 14-18 parts of a chain extender, and 0.5-2 parts of a catalyst;

[0034] The chain extender is a polyol and does not exceed 20% of bisphenol A. The catalyst is a quaternary ammonium salt catalyst, which is responsible for accelerating the reaction.

[0035] The resin is synthesized through a bisphenol A two-step epoxy synthesis process, and part of the bisphenol A is replaced by hexanediol, and a new epoxy resin is synthesized by heating with a primary bisphenol A epoxy resin under the action of a catalyst. Compared with traditional epoxy resins, the epoxy resin uses hexanediol as a flexible chain segment, which can significantly improve the flexibility and toughness of the resin, facilitate better impregnation and filling, and improve the performance of coatings and composite materials. At the same time, by controlling the proportion of hexanediol, the chemical resistance of the resin can maintain the level of type 9 bisphenol A epoxy, thereby improving the mechanical properties of the resin.

[0036] Wherein, the preparation method of the epoxy resin is:

[0037] Step 1: Pretreatment stage: prepare raw materials and reactor according to the formula ratio;

[0038] The reactor needs to be equipped with an agitator, temperature control and cooling system to ensure subsequent reactions.

[0039] Step 2: prepolymerization reaction stage, weighed bisphenol A, chain extender and hexylene glycol are put into a reaction kettle for reaction, and a catalyst is added;

[0040] Step 3, epoxidation reaction stage, adding primary bisphenol A epoxy resin after the prepolymer reaction is completed;

[0041] Through prepolymerization and epoxidation reactions, the two-step bisphenol A epoxy synthesis process is realized, providing process guarantee for the production of epoxy resin.

[0042] Step 4: Cooling stage: After the reaction is completed, the reactor is cooled to room temperature and subjected to vacuum degassing treatment.

[0043] Cooling and degassing can remove gases that may be produced during the reaction and improve the transparency and performance of the resin.

[0044] Through the two-step production process, the production reaction time of the resin is relatively short, the temperature fluctuation is small, and it is easy to control, which is conducive to obtaining stable product quality. At the same time, the synthesis process is consistent with type 9 epoxy, and the price of hexanediol is higher than bisphenol A, so that the epoxy resin can ensure mechanical properties while reducing costs and increasing efficiency, with greater economic benefits. More importantly, the coating compounded with the resin can meet the processing flexibility of tinplate easy-to-open covers, and maintain chemical resistance consistent with existing coatings, thereby improving applicability.

[0045] Wherein, the reaction process of the prepolymerization stage is:

[0046] A1, put the weighed bisphenol A, chain extender and hexylene glycol into a reactor, and ensure that the reactor is completely sealed;

[0047] Bisphenol A is part of the backbone structure of epoxy resin, while hexanediol is responsible for replacing part of bisphenol A, which can effectively improve the flexibility and toughness of the resin, and the chemical resistance of the resin can maintain the level of type 9 bisphenol A epoxy.

[0048] A2, slowly heat the reactor to 120-180℃, while keeping stirring to ensure that the materials are evenly mixed:

[0049] A3, after reaching the required temperature of the catalyst, add the catalyst and continue heating and stirring;

[0050] A4, continue the reaction and observe the viscosity change of the material in the reactor to ensure that the reaction is fully carried out;

[0051] A5, after 2-4 hours of reaction, a prepolymer is formed.

[0052] By adding hexanediol and chain extender in the prepolymerization stage, the chain segments in the resin molecular structure are more flexible, the resin has better fluidity after being made into coatings, and the construction leveling effect is better. In addition, the polyol molecular chains are longer, and they can act as a bridge in the resin molecules, connecting different resin molecular chains, thereby increasing the flexibility and toughness of the resin and ensuring the stability of the epoxy resin.

[0053] In the epoxy reaction stage, after adding the primary bisphenol A epoxy resin, it is necessary to continue heating to 150-200° C., react for 1-3 hours, and keep stirring.

[0054] The reaction rate is increased by heating, and the reactants are ensured to be evenly distributed in the reaction system by stirring, thereby improving the efficiency of the epoxy reaction.

[0055] Wherein, during the epoxidation reaction stage, a titration method is used in the reactor to monitor the change of epoxy groups during the reaction process to ensure that the epoxy equivalent is within the range of 3500-5500 g / eq.

[0056] The epoxy equivalent of the epoxy resin is 3500-5500 g / eq, and because part of hexanediol replaces bisphenol A, the flexibility of the resin is significantly improved. By controlling the proportion of hexanediol, the chemical resistance of the resin can basically maintain the level of type 9 bisphenol A epoxy.

[0057] Wherein, the processing steps of the cooling stage are:

[0058] B1, after the reaction is completed, slowly cool the reactor to room temperature;

[0059] Since epoxy resin will start to solidify when it reaches a certain temperature, it is necessary to ensure slow cooling to avoid a too fast cooling stage, which will cause the resin to solidify before the gas is completely released, leaving bubbles or defects;

[0060] B2, during the cooling process, slightly heats the resin so that the internal gas can reach the resin surface faster and be extracted by the vacuum system;

[0061] Heating can cause thermal motion of resin molecules, thereby accelerating the diffusion rate of gas molecules in the resin;

[0062] B3, at this time, the epoxy resin production is completed, and the epoxy resin is tested for tensile strength, flexibility, chemical resistance and other properties to ensure that the product meets the expected standards.

[0063] By heating and vacuum degassing, bubbles and defects in the resin can be effectively reduced, the transparency and mechanical properties of the product can be improved, and the stability of the epoxy resin can be ensured.

[0064] The chain extender can increase the length of the resin molecular chain, thereby increasing the molecular weight of the epoxy resin, thereby improving its physical and mechanical properties and heat resistance.

[0065] Polyols have longer molecular chains and can act as bridges in resin molecules, connecting different resin molecular chains, thereby increasing the flexibility and toughness of the resin.

[0066] The preparation method can flexibly control the curing time by adjusting the amount of catalyst used, thereby adapting to different processing requirements.

[0067] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0068] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An epoxy resin for food packaging coating, characterized in that: The epoxy resin is prepared from the following raw materials in weight ratio: 70-90 parts of bisphenol A, 10-30 parts of hexylene glycol, 30-50 parts of primary bisphenol A epoxy resin relative to the total epoxy equivalent, 14-18 parts of chain extender and 0.5-2 parts of catalyst; The chain extender is a polyol and does not exceed 20% of bisphenol A. The catalyst is a quaternary ammonium salt catalyst, which is responsible for accelerating the reaction.

2. The epoxy resin for food packaging coating according to claim 1, characterized in that: The preparation method of the epoxy resin is: Step 1: Pretreatment stage: prepare raw materials and reactor according to the formula ratio; Step 2: prepolymerization reaction stage, weighed bisphenol A, chain extender and hexylene glycol are put into a reaction kettle for reaction, and a catalyst is added; Step 3, epoxidation reaction stage, adding primary bisphenol A epoxy resin after the prepolymer reaction is completed; Step 4: Cooling stage: After the reaction is completed, the reactor is cooled to room temperature and subjected to vacuum degassing treatment.

3. The epoxy resin for food packaging coating according to claim 2, characterized in that: The reaction process of the prepolymerization stage is: A1, put the weighed bisphenol A, chain extender and hexylene glycol into a reactor, and ensure that the reactor is completely sealed; A2, slowly heat the reactor to 120-180℃, while keeping stirring to ensure that the materials are evenly mixed: A3, after reaching the required temperature of the catalyst, add the catalyst and continue heating and stirring; A4, continue the reaction and observe the viscosity change of the material in the reactor to ensure that the reaction is fully carried out; A5, after 2-4 hours of reaction, a prepolymer is formed.

4. The epoxy resin for food packaging coating according to claim 2, characterized in that: In the epoxy reaction stage, after adding the primary bisphenol A epoxy resin, it is necessary to continue heating to 150-200° C. for 1-3 hours while maintaining stirring.

5. The epoxy resin for food packaging coating according to claim 2, characterized in that: During the epoxidation reaction stage, the change of epoxy groups during the reaction process is monitored by titration in the reactor to ensure that the epoxy equivalent is within the range of 3500-5500 g / eq.

6. The epoxy resin for food packaging coating according to claim 2, characterized in that: The processing steps of the cooling stage are: B1, after the reaction is completed, slowly cool the reactor to room temperature; B2, during the cooling process, slightly heats the resin so that the internal gas can reach the resin surface faster and be extracted by the vacuum system; B3, at this time, the epoxy resin production is completed, and the epoxy resin is tested for tensile strength, flexibility, and chemical resistance to ensure that the product meets the expected standards.

7. The epoxy resin for food packaging coating according to claim 2, characterized in that: The chain extender can increase the length of the resin molecular chain, thereby increasing the molecular weight of the epoxy resin, thereby improving its physical and mechanical properties and heat resistance.

8. The epoxy resin for food packaging coating according to claim 2, characterized in that: The preparation method can flexibly control the curing time by adjusting the amount of the catalyst, thereby adapting to different processing requirements.

Images