A styrene-free unsaturated polyester resin and its preparation method

Abstract

The present invention relates to the technical field of unsaturated polyester resins, and mainly relates to a styrene-free unsaturated polyester resin and a preparation method thereof. The styrene-free unsaturated polyester resin provided by the present invention comprises an unsaturated polyester and a crosslinking diluent, and the crosslinking diluent comprises dimethacrylate and 4-methylstyrene. In the present invention, dimethacrylate and 4-methylstyrene are used together as the crosslinking diluent. The dimethacrylate with an oxygen atom at the β position has good copolymerization ability with the unsaturated polyester, and can promote the compatibility of 4-methylstyrene and the unsaturated polyester resin. By adjusting the molar ratio of the two and the weight ratio between the two and the unsaturated polyester resin, the physical properties of the cured product are comparable to those of the styrene system, and it has good low-temperature stability. By mixing different types of unsaturated polyesters, a styrene-free unsaturated polyester resin with good mechanical properties and good water resistance can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of unsaturated polyester resins, and particularly to a styrene-free unsaturated polyester resin and a preparation method thereof. Background Art

[0002] Unsaturated polyester resins have good physical properties, corrosion resistance, gloss, and fullness, and are easy to process with low cost. They are widely used in industries such as fiberglass composite materials, gel coat resins, and handicrafts. Unsaturated polyesters are mainly obtained by polycondensation of diols and dianhydrides, and then diluted with unsaturated monomers to obtain a polymer solution with a lower viscosity. In the processing of traditional unsaturated polyester resins, styrene is the most commonly used reactive diluent monomer. However, styrene has a relatively high saturated vapor pressure at room temperature, is easy to volatilize, and has a pungent and special smell, which has an irritating effect on the eyes and the mucous membranes of the upper respiratory tract. Therefore, its volatility and toxic side effects will inevitably cause great harm to the environment and the health of operators. Therefore, the development of low-styrene or styrene-free unsaturated polyester resins has become a hot research topic at home and abroad.

[0003] At present, a large number of literatures have reported on styrene-free unsaturated polyester resin technologies. The monomer substitution technologies for styrene-free can generally be divided into two categories. The first category uses styrene-like monomers, and the second category is methacrylate monomers. Styrene-like substitution monomers include 4-tert-butylstyrene, 4-methylstyrene, vinylstyrene, etc. The substitution effect of this type of monomer is better, and the properties of the cured products obtained are similar, but they have a large volatility and a relatively high price. The second category of methacrylate monomers is cheap, but generally common methacrylate monomers, fumarates or maleates are electron-deficient monomers, and their copolymerization activity is poor, resulting in a reduction in the mechanical properties of the cured products. At the same time, conventional methacrylate monomers are easily inhibited by oxygen in the air, resulting in insufficient polymerization and the surface of the product being prone to stickiness.

[0004] Therefore, it is of great significance to develop a styrene-free unsaturated polyester resin with high copolymerization ability, good mechanical properties, good low-temperature stability and water resistance. Summary of the Invention

[0005] The purpose of the present invention is to provide a styrene-free unsaturated polyester resin and a preparation method thereof.

[0006] To achieve this purpose, the present invention adopts the following technical solutions:

[0007] The first aspect of the present invention provides a styrene-free unsaturated polyester resin, and the specific technical solution is as follows:

[0008] A styrene-free unsaturated polyester resin, comprising an unsaturated polyester resin and a crosslinking diluent, wherein the crosslinking diluent comprises dimethacrylate and 4-methylstyrene; the molar ratio of the dimethacrylate to the 4-methylstyrene is 1:2.5 to 3.5.

[0009] In some embodiments of the present invention, the dimethacrylate is selected from any one of glycerol dimethacrylate, diethylene glycol dimethacrylate, and triethylene glycol dimethacrylate.

[0010] In some embodiments of the present invention, the molar ratio of the dimethacrylate to the 4-methylstyrene is 1:3.

[0011] In some embodiments of the present invention, when the crosslinking diluent is diethylene glycol dimethacrylate, the double bond molar content of the diethylene glycol dimethacrylate and the 4-methylstyrene is 35% to 40% of the double bond molar content of styrene by weight.

[0012] In some embodiments of the present invention, the unsaturated polyester resin is selected from one or a combination of UP-196, UP-667, UP-196-2, and UP-988-3.

[0013] In some embodiments of the present invention, the unsaturated polyester is formed by the polycondensation of a diol and a diacid; the diol is one or several of propylene glycol, ethylene glycol, neopentyl glycol, dipropylene glycol, glycerol, dicyclopentadiene, and trimethylolpropane; the diacid is one or several of isophthalic acid, phthalic acid, maleic acid, adipic acid, fumaric acid, tetrahydrophthalic anhydride, and terephthalic acid.

[0014] In some embodiments of the present invention, the crosslinking diluent further comprises one or several of divinylbenzene, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate.

[0015] In some embodiments of the present invention, the unsaturated polyester is dissolved in the crosslinking agent to obtain a styrene-free unsaturated resin, and cobalt octoate is used as an accelerator and methyl ethyl ketone peroxide is used as a curing agent for room temperature curing, or benzoyl peroxide and tert-butyl peroxybenzoate are used as curing agents for high temperature curing.

[0016] In some embodiments of the present invention, it further comprises 0.08 to 0.12 wt% of paraffin wax.

[0017] The second aspect of the present invention provides a method for preparing a styrene-free unsaturated polyester resin, comprising the following steps:

[0018] Step 1: Esterify a diol and a diacid in a suitable alcohol-acid ratio to obtain an unsaturated polyester;

[0019] Step 2: Add the unsaturated polyester obtained in Step 1 to dimethacrylate and 4-methylstyrene crosslinking agent, and mix evenly to obtain a mixed material.

[0020] Step 3: Adjust the gel time of the mixed material by adding an inhibitor to obtain a styrene-free unsaturated polyester resin.

[0021] In some embodiments of the present invention, the molar ratio of the dimethacrylate and the 4-methylstyrene in Step 2 is 1:2.5 - 3.5.

[0022] In some embodiments of the present invention, divinylbenzene, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate or one or more of them can also be added in Step 2.

[0023] In some embodiments of the present invention, one or more of an antifoaming agent, a leveling agent, and a wetting and dispersing agent are also added in Step 3.

[0024] In some embodiments of the present invention, the inhibitor in Step 3 includes one or two of hydroquinone and methylhydroquinone.

[0025] In some embodiments of the present invention, paraffin wax is also added in Step 3, the addition temperature is controlled above 60°C, and the mass of the added paraffin wax is 0.08 - 0.12% of the mass of the mixed material.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. For the styrene-free unsaturated polyester resin provided by the present invention, dimethacrylate and 4-methylstyrene are used together as a crosslinking diluent. The dimethacrylate with an oxygen atom at the β-position has good copolymerization ability with the unsaturated polyester resin, and can promote the compatibility of 4-methylstyrene and the unsaturated polyester resin. By adjusting the molar ratio of the two and the weight ratio between the two and the unsaturated polyester resin, the physical properties of the cured product are comparable to those of the styrene system.

[0028] 2. The present invention preferably uses dimethacrylate and 4-methylstyrene together as a crosslinking diluent to obtain a styrene-free unsaturated polyester resin with good low-temperature stability. By mixing different types of unsaturated polyester resins, a styrene-free unsaturated polyester resin with good mechanical properties and water resistance can be obtained. Specific Embodiments

[0029] The styrene-free unsaturated polyester resin and its preparation method of the present invention will be described in detail below.

[0030] The first aspect of the present invention provides a styrene-free unsaturated polyester resin, comprising an unsaturated polyester resin and a crosslinking diluent, wherein the crosslinking diluent comprises dimethacrylate and 4-methylstyrene (VT); the molar ratio of the dimethacrylate to VT is 1:2.5 to 3.5.

[0031] In the present invention, two types of styrene alternative monomers are combined. The first type of styrene alternative monomer is VT, and the second type of methacrylate monomer is a methacrylate containing β-hydroxy or alkoxy group, which has good copolymerization activity with the α,β-unsaturated double bond and cyclohexene in the unsaturated polyester. It is speculated that the β-oxygen atom may attack the carbonyl group to form a 5-membered ring, disrupting the conjugation between the acrylic double bond and the carbonyl group, increasing the electron cloud density on the acrylic double bond, and thus enabling it to copolymerize with the electron-deficient α,β-unsaturated double bond. As shown in the following formula (1):

[0032]

[0033] In some embodiments of the present invention, the dimethacrylate is selected from any one of glycerol dimethacrylate (GL-DMA), diethylene glycol dimethacrylate (DEG-DMA), and triethylene glycol dimethacrylate (TEG-DMA). Experiments have shown that the dimethacrylate with an oxygen atom at the β-position has good copolymerization ability with the unsaturated polyester resin and promotes the compatibility of VT and the unsaturated polyester resin.

[0034] In some preferred embodiments of the present invention, the molar ratio of the dimethacrylate to VT is 1:3. During the experiment, it was found that when the dimethacrylate / VT with a molar ratio of 1:1 was used as the crosslinking diluent, the physical properties of the cured product were quite different from those of the styrene / UP196 system. The increase in the amount of VT contributed to obtaining properties similar to those of the styrene-cured product. When the molar ratio of the dimethacrylate to VT is 1:3, the physical properties of the unsaturated polyester resin approach or reach those of the styrene-system cured product. When the molar ratio of the dimethacrylate to VT is further increased to 1:4, the sample is very brittle and cannot be taken out of the mold. Therefore, the molar ratio of the dimethacrylate to VT is preferably 1 to 3.

[0035] In some embodiments of the present invention, when the crosslinking diluent is DEG-DMA, the molar content of double bonds of DEG-DMA and VT is the same as that of styrene with a double bond molar content of 35% to 40% by weight. During the experiment, it was found that when the molar content of double bonds of both DEG-DMA / VT is equivalent to that of styrene with 35% by weight, and the molar ratio of DEG-DMA / VT = 1 / 3, the degree of curing reaches 93.7%, approaching the degree of curing of the styrene / UP system (95.6%). The physical properties obtained are approximately equivalent to those of the product after curing of 80% of the styrene / UP system. Secondly, by changing the weight ratio of DEG-DMA / VT to UP, when the double bond content of both DEG-DMA / VT is equivalent to that of styrene with 40%, and the molar ratio of DEG-DMA / VT = 1 / 3, the main physical properties obtained, such as the yield strength, have been comparable to those of the styrene / UP system, and other physical property indicators have also been improved accordingly.

[0036] In some embodiments of the present invention, the unsaturated polyester resin is selected from one or a combination of UP-196, UP-667, UP-196-2, and UP-988-3.

[0037] The UP-196 unsaturated polyester resin is a light yellow transparent viscous liquid with a solid content of 64% to 70%; viscosity (25°C, 450 - 500 mpa.s); acid value: 17 - 25 mgKOH / g; good toughness and high impact strength, and it is a general-purpose reinforced unsaturated resin. Propylene glycol, phthalic anhydride, and maleic anhydride are used to synthesize a polyester with a certain molecular weight. The crosslinking agent is vinyltoluene (VT) and hydroxyethyl methacrylate (HPMA).

[0038] The UP-667 unsaturated polyester resin is a yellow transparent viscous liquid with a solid content of 72% - 74%, viscosity (25°C, 1400 - 1500 mpa.s); acid value: 16 - 22 mgKOH / g; of the dicyclopentadiene type, with good air-drying property, and is specifically used for unsaturated insulating paint. Ethylene glycol, diethylene glycol, dicyclopentadiene, and maleic acid are used to synthesize the polyester, and the diluent is vinyltoluene (VT), hydroxyethyl methacrylate (HEMA), and divinylbenzene (DVB).

[0039] The UP-196-2 unsaturated polyester resin adds materials such as ethylene glycol and diethylene glycol on the basis of UP-196 to increase toughness and reduce costs. Its solid content is 64 - 70%; viscosity (25°C, 450 - 500 mpa.s); acid value: 17 - 25 mgKOH / g; good toughness and high impact strength, and it is a general-purpose reinforced unsaturated resin.

[0040] UP-988-3 unsaturated polyester resin has a solid content of 66% - 69%; viscosity (25°C, 900 - 1100 mPa·s); acid value: 18 - 22 mgKOH / g; high hardness and good pearlescent arrangement, and it is an unsaturated resin for buttons. Neopentyl glycol, propylene glycol, diethylene glycol, phthalic anhydride, and maleic anhydride are used to synthesize a polyester with a certain molecular weight. The crosslinking agent uses vinyltoluene (VT), hydroxypropyl methacrylate (HPMA), and defoaming agents, leveling agents and other additives are added, and the addition amount is 0.1 - 0.3 wt%. In some embodiments of the present invention, the crosslinking diluent further includes one or more of divinylbenzene (DVB), hydroxyethyl methacrylate (HEMA), and hydroxypropyl methacrylate (HPMA). In some embodiments of the present invention, when DVB is used to replace part of VT, the impact resistance of the spline is better, and the maximum bending stress decreases slightly. In some embodiments of the present invention, when HEMA and UP are cured, the obtained spline has very high impact resistance. Therefore, an appropriate amount of HEMA can be added to some formulations to make up for the lack of impact resistance.

[0041] In some embodiments of the present invention, the unsaturated polyester is formed by condensation polymerization of diols such as propylene glycol, ethylene glycol, neopentyl glycol, dipropylene glycol, glycerol, dicyclopentadiene, trimethylolpropane, etc. and dibasic acids such as isophthalic acid, phthalic acid, maleic acid, adipic acid, fumaric acid, tetrahydrophthalic anhydride, terephthalic acid, etc. into polyesters with different molecular structures and different molecular weights. This unsaturated polyester is dissolved in the above crosslinking agent without styrene to obtain a styrene-free unsaturated resin. Cobalt isooctanoate is used as a promoter, and methyl ethyl ketone peroxide is used as a curing agent for room temperature curing, or benzoyl peroxide, tert-butyl peroxybenzoate and other heat curing agents can be used for high temperature curing. Some application models also add defoaming agents, leveling agents, wetting and dispersing agents and other additives.

[0042] In some embodiments of the present invention, it also includes 0.08 - 0.12 wt% of paraffin, for example, it can be 0.08 - 0.10 wt%, 0.10 - 0.12 wt%, 0.09 - 0.11 wt%, and more preferably 0.1 wt%. Experiments have found that adding 0.1 wt% of paraffin can not only make the spline pass the boiling water test, but also has excellent mechanical properties. As the amount of paraffin increases, the hydrolysis resistance is better, but the mechanical properties decrease, which may be caused by the poor compatibility of paraffin.

[0043] The second aspect of the present invention provides a method for preparing a styrene-free unsaturated polyester resin, including the following steps:

[0044] Step 1: Esterify the diol and the dibasic acid in a suitable alcohol-acid ratio to obtain an unsaturated polyester;

[0045] Step 2: Add the unsaturated polyester obtained in Step 1 to dimethacrylate and 4-methylstyrene crosslinking agent, and mix evenly to obtain a mixed material.

[0046] Step 3: Adjust the gel time of the mixed material by adding an inhibitor to obtain a styrene-free unsaturated polyester resin.

[0047] In some embodiments of the present invention, the molar ratio of the dimethacrylate and VT in Step 1 is 1:2.5 - 3.5, preferably 1:3.

[0048] In some embodiments of the present invention, one or more of DVB, HEMA, and HPMA can also be added in Step 2.

[0049] In some embodiments of the present invention, one or more of an antifoaming agent, a leveling agent, and a wetting and dispersing agent are also added in Step 3.

[0050] In some embodiments of the present invention, the inhibitor in Step 3 includes one or two of hydroquinone and methylhydroquinone.

[0051] In some embodiments of the present invention, paraffin wax is also added in Step 3, the addition temperature is controlled above 60°C, and the mass of the added paraffin wax is 0.08 - 0.12% of the mass of the mixed material, preferably 0.1%.

[0052] The following further details the specific embodiments of the present invention in conjunction with preferred embodiments. When the embodiments give a numerical range, it should be understood that unless otherwise specified in the present invention, any value between the two endpoints of each numerical range and any value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art of this technology. In addition to the specific methods, equipment, and materials used in the embodiments, as those skilled in the art of this technology master the prior art and the present invention is described, any method, equipment, and materials similar or equivalent to the methods, equipment, and materials described in the embodiments of the present invention can also be used to implement the present invention.

[0053] Example 1

[0054] A styrene-free unsaturated polyester resin, comprising an unsaturated polyester resin and a crosslinking diluent, the grade of the unsaturated polyester resin is: UP-196; the crosslinking diluent is DEG-DMA and VT.

[0055] A preparation method of a styrene-free unsaturated polyester resin, comprising the following steps:

[0056] Step 1: Put propylene glycol, phthalic anhydride, and maleic anhydride into the reaction kettle according to an alcohol-acid ratio of 1.1. Carry out esterification reaction to remove water at about 160°C. After water removal, control the distillate head temperature below 102°C, raise the material temperature to 205°C and continue the reaction until the acid value of the material is 60 - 65 mg KOH / g. The atmospheric pressure reaction time is about 8 hours. Then carry out a vacuum reaction, control the pressure at -0.095 MPa, and the time is about 2 hours. Control the end point acid value at 26 - 29 mg KOH / g to obtain unsaturated polyester, and its structural formula is as follows:

[0057]

[0058] Step 2: Cool the unsaturated polyester obtained in Step 1 to 160°C and pump it from the reaction kettle to the dilution kettle. The dilution kettle is pre-added with a certain proportion of DEG-DMA and VT. Control the dilution speed to keep the temperature of the material in the dilution kettle below 85°C, and complete the dilution and uniform mixing in about 1.5 hours;

[0059] Step 3: After dilution, test the gel time and viscosity, add inhibitor to complete the adjustment of the gel time, and add a small amount of VT to complete the adjustment of the viscosity;

[0060] Step 4: Pour the adjusted material into the mold, add 1% MEKP (curing agent) and 1% cobalt salt solution, cure at room temperature for 24 hours, and then post-cure at 80°C for 2 hours to obtain a GL-DMA / VT / UP196 styrene-free unsaturated polyester resin casting block.

[0061] Example 2

[0062] A styrene-free unsaturated polyester, comprising unsaturated polyester resin and crosslinking diluent. The grade of the unsaturated polyester is: UP-196-2; the crosslinking diluent is GL-DMA and VT;

[0063] The structural formula of the unsaturated polyester UP-196-2 is:

[0064]

[0065] A preparation method of a styrene-free unsaturated polyester resin, comprising the following steps:

[0066] Step 1: Mix GL-DMA and VT according to a molar ratio of 1:3 to prepare a crosslinking diluent;

[0067] Step 2: Add unsaturated polyester UP196 to the dilution kettle. The dilution kettle is pre-added with the crosslinking diluent prepared in Step 1. Control the dilution speed to keep the temperature of the material in the dilution kettle below 85°C, and complete the dilution and uniform mixing in about 1.5 hours;

[0068] Step 3: After dilution, test the gel time, add inhibitor, and complete the adjustment of the gel time;

[0069] Step 4: Pour the adjusted materials into a mold, add 1% MEKP as the curing agent and 1% cobalt salt solution, cure at room temperature for 24 h, and then post-cure at 80 °C for 2 h to obtain a GL-DMA / VT / UP196 styrene-free unsaturated polyester resin casting block.

[0070] Example 3

[0071] A styrene-free unsaturated polyester resin, comprising an unsaturated polyester resin and a crosslinking diluent, wherein the grade of the unsaturated polyester is: UP988-3; the crosslinking diluent is GL-DMA and VT;

[0072] The structural formula of the unsaturated polyester UP988-3 is:

[0073]

[0074] A preparation method of a styrene-free unsaturated polyester resin, comprising the following steps:

[0075] Step 1: Mix GL-DMA and VT in a molar ratio of 1:3 to prepare a crosslinking diluent;

[0076] Step 2: Add the unsaturated polyester resin UP988-3 to a dilution kettle, and the crosslinking diluent prepared in Step 1 has been added to the dilution kettle in advance. Control the dilution speed to keep the temperature of the materials in the dilution kettle below 85 °C, and complete the uniform mixing of dilution in about 1.5 h;

[0077] Step 3: After the dilution is completed, test the gel time and add an inhibitor to complete the adjustment of the gel time;

[0078] Step 4: Pour the adjusted materials into a mold, add 1% MEKP as the curing agent and 1% cobalt salt solution, cure at room temperature for 24 h, and then post-cure at 80 °C for 2 h to obtain a GL-DMA / VT / UP988-3 styrene-free unsaturated polyester resin casting block.

[0079] Example 4

[0080] A styrene-free unsaturated polyester resin, comprising an unsaturated polyester resin and a crosslinking diluent, wherein the grade of the unsaturated polyester is: UP667; the crosslinking diluent is GL-DMA and VT;

[0081] The structural formula of the unsaturated polyester UP667 is:

[0082]

[0083] A preparation method of a styrene-free unsaturated polyester resin, comprising the following steps:

[0084] Step 1: Mix GL-DMA and VT in a molar ratio of 1:3 to prepare a crosslinking diluent.

[0085] Step 2: Add unsaturated polyester resin UP667 to a dilution kettle, in which the crosslinking diluent prepared in Step 1 has been added in advance. Control the dilution rate to keep the temperature of the materials in the dilution kettle below 85°C, and complete the uniform mixing by dilution in about 1.5 h.

[0086] Step 3: After the dilution is completed, test the gel time and add an inhibitor to complete the adjustment of the gel time.

[0087] Step 4: Pour the adjusted materials into a mold, add 1% MEKP as a curing agent and 1% cobalt salt solution, cure at room temperature for 24 h, and then post-cure at 80°C for 2 h to obtain a GL-DMA / VT / UP667 styrene-free air-dry resin casting block.

[0088] 1. Influence of the proportion of crosslinking monomers

[0089] Dimethacrylate esters DEG-DMA, TEG-DMA, GL-DMA and their combinations with VT are used to crosslink and cure unsaturated polyester. Through Soxhlet extraction, it is found that these monomers can react with unsaturated polyester, and the introduction of VT can improve the physical properties after curing. The physical properties of the cured products are adjusted by changing the molar ratio of the two and their ratio to unsaturated polyester. The results are as follows.

[0090] 1.1 DEG-DMA / VT system

[0091] Table 1 Properties of DEG-DMA / VT / UP196 cured products

[0092]

[0093]

[0094] Note: Type and dosage of accelerator: 1% cobalt octoate solution, 1% methyl ethyl ketone peroxide solution.

[0095] As can be seen from Table 1, when the fixed crosslinking diluent DEG-DMA / VT = 1 / 2, with the increase in the total dosage of DEG-DMA / VT (Groups 1 and 3), the physical properties are improved, indicating that the amount of crosslinking diluent cannot be too small, otherwise the crosslinking is incomplete. When the molar ratio of DEG-DMA / VT increases from 1 / 1 to 1 / 2 to 1 / 3 (Groups 2, 3, and 4), the physical properties continue to rise. This is because the structure of VT is similar to that of styrene, while DEG-DMA is too soft. Therefore, the increase in the dosage of VT helps to obtain properties similar to those of styrene-cured products. When DEG-DMA / VT = 1 / 3 and the total dosage is equivalent to 35% of styrene, the tensile properties of the cured product reach the level of 80% styrene / UP196. Further increasing the total dosage of DEG-DMA / VT, equivalent to 40% of styrene, the tensile properties are improved to the level of 90% styrene / UP196, and the flexural properties reach 77% of the level of styrene / UP196.

[0096] 1.2 TEG-DMA / VT system

[0097] Table 2 Properties of TEG-DMA / VT / UP196 cured products

[0098]

[0099]

[0100] Note: Type and dosage of accelerator: 1% cobalt octoate solution, 1% methyl ethyl ketone peroxide solution.

[0101] As can be seen from Table 2, generally speaking, TEG-DMA / VT shows the same trend as DEG-DMA / VT with respect to the molar ratio and weight ratio. However, perhaps because TEG-DMA is softer than DEG-DMA, the overall properties of the unsaturated polyester products cured by TEG-DMA / VT are not as good as those of the latter.

[0102] 1.3 GL-DMA / VT system

[0103] Table 3 Properties of GL-DMA / VT / UP196 cured products

[0104]

[0105]

[0106] Note: Type and dosage of accelerator: 1% cobalt octoate solution, 1% methyl ethyl ketone peroxide solution.

[0107] Table 3 results show that with the increase of VT, the physical properties continuously improve. When TEG-DMA / VT = 1 / 3 and the total dosage is equivalent to 35% or 40% of styrene (Groups 3 and 4), especially in Group 4, the physical properties of the cured products obtained are already very close to those of styrene / UP196. For example, the tensile properties such as elastic modulus / yield strength / fracture growth rate are close to or exceed those of the styrene / UP system. In terms of flexural properties, it also reaches 90% of the styrene / UP system, and the impact resistance is comparable.

[0108] 2. Influence of unsaturated polyester resin types

[0109] After investigating the influence of the dimethacrylate structure, its molar ratio with VT, and the addition amount on the physical properties of the cured products of unsaturated polyester resins, considering that UP196 contains approximately 11% maleate with relatively poor copolymerization activity, the influence of the types of unsaturated polyester resins on the physical properties of the cured products was further studied.

[0110] 2.1 Air-drying unsaturated polyester resin UP667

[0111] Table 4 Properties of dimethacrylate / VT / UP7667 cured products

[0112]

[0113]

[0114] Note: Types and dosages of accelerators: 1% cobalt octoate solution, 1% methyl ethyl ketone peroxide solution.

[0115] It can be seen from Table 4 that the air-drying unsaturated polyester resin crosslinked with styrene is relatively brittle. Using dimethacrylates with flexible chain segments can effectively improve the brittleness of the air-drying unsaturated polyester resin, and the flexural properties of DEG-DMA / VT have exceeded those of styrene / UP667 (the tensile property specimens are all brittle fractures), and TEG-DMA / VT or GL-DMA / VT also significantly improve the tensile properties and impact resistance of UP667, but the flexural properties decrease. Combining the results of Tables 1 - 3, the tensile properties and flexural properties are somewhat contradictory to each other to a certain extent.

[0116] 2.2 High fumarate unsaturated polyester resin 196-2

[0117] Table 5 Properties of dimethacrylate / VT / UP19-2 cured products

[0118]

[0119]

[0120] Note: Types and dosages of accelerators: 1% cobalt octoate solution, 1% methyl ethyl ketone peroxide solution.

[0121] The content of fumarate in UP196-2 is approximately 97%, and its copolymerization activity with crosslinking diluents is also expected to be higher. As can be seen from Table 4, the performance of GL-DMA / UP196-2 is comparable to that of styrene / UP196-2, and is also comparable to the tensile and impact strengths of styrene / UP196-2, with similar bending properties, indicating that styrene-free unsaturated polyester resins can be achieved by using appropriate UP resins and crosslinking diluents.

[0122] 3. Influence of curing conditions

[0123] Considering that the optimal curing conditions may vary for different unsaturated polyester resin compositions, taking UP / glycerol dimethacrylate / 4-methylstyrene as an example, the influence of curing agents, curing time, etc. on the degree of curing was investigated, and the results are shown in Table 6.

[0124] Table 6 Different curing conditions and results

[0125]

[0126]

[0127] As can be seen from Table 6, by comparing between Group 1 and Group 2, and between Group 5 and Group 6, it can be known that after the room temperature curing time is greater than 24 h, the room temperature curing duration has little effect on the degree of curing. By comparing between Group 1 and Group 3, and between Group 5 and Group 7, it can be known that after the 80 °C curing time is greater than 2 h, the 80 °C curing duration has little effect on the degree of curing. By comparing between Group 1 and Group 5, and between Group 2 and Group 6, it can be known that the dosage of the curing agent also has little effect on the degree of curing. Generally speaking, the dosage of the curing agent and the curing time have little effect on the degree of curing. Therefore, the initial curing scheme (1% MEKP, 1% cobalt salt, cured at room temperature for 24 h, post-cured at 80 °C for 2 h) can still be adopted in subsequent research.

[0128] 4. Low-temperature stability test

[0129] To understand the low-temperature stability of the UP / methacrylate / 4-methylstyrene system, 6 compositions were selected for low-temperature testing, and the specific compositions are shown in Table 7. These 6 compositions were placed in the refrigerator freezer (5 °C) and observed once every other day. The results are shown in Table 7.

[0130] Table 7 Compositions and low-temperature stability of styrene-free UP compositions

[0131] UP DMA / Mass percentage VT Before refrigeration Stratification time Group 1 61.92％ DEG - DMA / 9.7% 28.38％ Yellow and transparent ＜46h Group 2 60.85％ TEG - DMA / 11.26% 27.89％ Yellow and transparent > 12 days Group 3 60.80％ GL - DMA / 11.33% 27.87％ Yellow and transparent > 12 days Group 4 58.73％ DEG - DMA / 10.51% 30.76％ Yellow and transparent ＜46h Group 5 57.63％ TEG - DMA / 12.18% 20.18％ Yellow and transparent ＜46h Group 6 57.58％ GL - DMA / 12.26% 30.16％ Yellow and transparent > 12 days

[0132] The results in Table 7 show that GL-DMA / VT / UP has good low-temperature stability and remains a homogeneous liquid after long-term (>12 days) low-temperature storage, while DEG-DMA / VT / UP shows stratification within 2 days; the TEG-DMA / VT / UP system has good low-temperature stability and can be stored for a long time when the usage amounts of TEG-DMA and VT are low, but has poor stability and shows stratification within 2 days when the usage amounts are high. Considering all the results, GL-DMA / VT / UP has the best low-temperature stability and can be stored at low temperature for a long time.

[0133] 5. Water resistance test

[0134] The DEG-DMA / VT / UP and GL-DMA / VT / UP systems with better mechanical properties were selected, and different types of UP were replaced for the water resistance test. The test was carried out in a water bath at 90 - 95 °C, and the results are shown in Table 8.

[0135] Table 8 Water resistance test results of UP compositions

[0136]

[0137] The styrene-free UP compositions of the 196 series all have poor water resistance, and whiteening appears on the surface after short-term boiling; UP667 and UP JC-S28 have better water resistance and do not show whiteening under boiling. In addition, when mixing UPs, when the content of UP667 is high (50%), the water resistance of the composition is good and no whiteening occurs. However, when the content of UP667 is low (<25%), the water resistance of the composition is poor.

[0138] 6. Water resistance solutions

[0139] 6.1 Water resistance solutions for GL-DMA / VT / UP compositions

[0140] The water resistance of the GL-DMA / VT / UP system is insufficient. Through mechanism analysis, it should be that the surface of GL-DMA / VT is inhibited by oxygen polymerization, similar to UP / styrene, but more serious than the latter. To verify this reasoning, during the curing process of the sample, part was covered with a glass slide and part was completely exposed. The boiling test found that the samples in the air-insulated part did not turn white or sticky, while the exposed part was the opposite. Therefore, the GL-DMA / VT / UP system also needs to avoid oxygen polymerization.

[0141] Measures to avoid or reduce air inhibition are to use paraffin. By changing the addition amount of paraffin, the effects of paraffin on the boiling water performance and physical properties are investigated. It is found through experiments that adding 0.1% paraffin can not only enable the test specimens to pass the boiling water test, but also have excellent mechanical properties. As the amount of paraffin increases, the hydrolysis resistance is better, but the mechanical properties decline, which may be caused by the poor compatibility of paraffin. The results are shown in Table 9.

[0142] Table 9 Effects of Paraffin and Air on the Water Resistance of GL-DMA / VT / UP Composition

[0143]

[0144] Note: Curing system: Curing agent: M50 1%, cobalt salt solution 1%; Water resistance test: Boiling water in a water bath at >90°C for >2 h.

[0145] 6.2 Mechanical Property Test of GL-DMA / VT / UP Composition

[0146] The test results of the mechanical properties of the GL-DMA / VT / UP composition are shown in Table 10.

[0147] Table 10 Test Results of the Mechanical Properties of Styrene-Free UP Composition

[0148]

[0149]

[0150] Note: Default curing system: Curing agent M50 1%, cobalt salt solution 1%.

[0151] It can be seen from Table 10 that the formulation with 0.1% paraffin added is very similar to the mechanical properties of UP / styrene. As the amount of paraffin increases, the yield strength, maximum bending stress, and impact performance all decline, indicating that paraffin affects the internal properties of the material.

[0152] The above embodiments merely illustrate the principles and effects of the present invention, rather than limiting the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. An unsaturated polyester resin without styrene, characterized in that, The invention comprises an unsaturated polyester resin and a cross-linking diluent. The cross-linking diluent comprises dimethacrylate and 4-methylstyrene. The molar ratio of the dimethacrylate to the 4-methylstyrene is 1:2.5-3.

5.

2. The styrene-free unsaturated polyester resin according to claim 1, wherein, The dimethacrylate is selected from any one of glycerol dimethacrylate, diethylene glycol dimethacrylate, and triethylene glycol dimethacrylate.

3. The styrene-free unsaturated polyester resin according to claim 1, wherein The molar ratio of the dimethacrylate to the 4-methylstyrene is 1:

3.

4. The styrene-free unsaturated polyester resin according to claim 1, wherein, Include any of the following characteristics: 1) The unsaturated polyester resin is one or a combination of UP-196, UP-667, UP-196-2, and UP-988-3; 2) The unsaturated polyester is prepared by shrinkage polymerization of a diol and a dibasic acid; the diol is one or more of propylene glycol, ethylene glycol, neopentyl glycol, dipropylene glycol, glycerol, dicyclopentadiene, and trimethylolpropane; and the dibasic acid is one or more of isophthalic acid, phthalic acid, maleic acid, adipic acid, fumaric acid, tetrahydrophthalic anhydride, and terephthalic acid.

5. The styrene-free unsaturated polyester resin according to claim 1, wherein The cross-linking diluent further comprises one or more of divinylbenzene, hydroxyethyl methacrylate, and hydroxypropyl methacrylate.

6. The styrene-free unsaturated polyester resin according to claim 1, wherein The unsaturated polyester is dissolved in the crosslinking agent to obtain a styrene-free unsaturated resin, which is cured at room temperature using cobalt isooctanoate as an accelerator and methyl ethyl ketone peroxide as a curing agent, or cured at high temperature using benzoyl oxide and tert-butyl perbenzoate as curing agents.

7. The styrene-free unsaturated polyester resin according to claim 1, wherein, The invention also includes 0.08-0.12 wt% of paraffin wax.

8. A method for preparing a styrene-free unsaturated polyester resin according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1: esterifying diol and dibasic acid at a suitable alcohol-acid ratio to obtain unsaturated polyester; Step 2: adding the unsaturated polyester prepared in step 1 to dimethacrylate and 4-methylstyrene crosslinking agent, and uniformly mixing to obtain a mixed material; the molar ratio of the dimethacrylate to the 4-methylstyrene is 1:2.5-3.5; Step 3: Add a polymerization inhibitor to the mixture to adjust the gel time to obtain a styrene-free unsaturated polyester resin.

9. The preparation method of the styrene-free unsaturated polyester resin according to claim 8, characterized in that, Also includes one or more of the following characteristics: 1) adding one or more of divinylbenzene, hydroxyethyl methacrylate, and hydroxypropyl methacrylate in step 2; 2) In step 3, one or more of a defoaming agent, a leveling agent, and a wetting and dispersing agent are also added; 3) The polymerization inhibitor in step 3 includes one or both of hydroquinone and methylhydroquinone; 4) Paraffin is also added in step 3, the addition temperature is controlled to be above 60° C., and the mass of the added paraffin is 0.08-0.12% of the mass of the mixed material.

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