Cardanol phenolic resin and preparation thereof, adhesion promoter, vulcanized rubber composition and rubber product

Abstract

The invention discloses cardanol phenolic resin and preparation thereof, an adhesion promoter, a vulcanized rubber composition and a rubber product. The cardanol phenolic resin is obtained by taking crude cardanol and paraformaldehyde as raw materials, carrying out condensation polymerization reaction in a solvent under the action of an acid catalyst, and separating after reaction. The adhesion promoter of the rubber product comprises a methylene acceptor and a methylene donor, and the methylene acceptor is the cardanol phenolic resin. The vulcanized rubber composition for the rubber product comprises the adhesion promoter. A rubber product is obtained by hot-pressing and vulcanizing a layered material comprising alternately stacked mixed rubber sheets and EP impregnated canvas, and the mixed rubber sheets are obtained by mixing the vulcanized rubber composition. According to the cardanol phenolic resin, non-grain bio-based raw materials are used, the cardanol phenolic resin is green, environmentally friendly and low in production cost, and the cardanol phenolic resin can achieve reliable bonding between rubber and a reinforcing material, especially gum dipping canvas.

Description

Technical Field

[0001] This invention relates to the field of polymer processing aids, and in particular to a cashew phenolic resin and its preparation method, an adhesion promoter for rubber products, a vulcanized rubber composition for rubber products, and a rubber product. Background Technology

[0002] Rubber products, such as conveyor belts and tires, generally require reinforcing materials like steel wires or fibers as skeleton materials. This necessitates maintaining good adhesion between the vulcanized rubber and the reinforcing materials. Typically, adhesion-promoting systems are added to maintain this adhesion. Existing adhesion-promoting systems generally include resorcinol or resorcinol resin as methylene acceptors and hexamethylenetetramine (HMT) or hexamethoxymethylmelamine (HMMM) as methylene donors. During vulcanization, the methylene acceptors and methylene donors react to form a resorcinol-formaldehyde resin network. This network structure improves the physical, mechanical, and adhesive properties of the vulcanized rubber and provides excellent connection and transition between the rubber compound and the steel wire adhesive layer after the adhesive layer is formed.

[0003] In existing technologies, resorcinol monomers are commonly used as methylene acceptor adhesives. However, due to the low smoke point of resorcinol, harmful substances are released during the rubber compounding process (150℃~200℃), thus it is gradually being replaced by pre-condensed phenolic resins. In existing technologies, styrene-modified resorcinol-formaldehyde resins have very low free resorcinol content (1-5%) and are less prone to fuming. However, a significant drawback is its significantly reduced reactivity; the resulting network is far less robust than networks constructed in situ with resorcinol monomers, leading to a noticeable decline in product performance. Furthermore, resorcinol is expensive; the price of commonly available industrial-grade resorcinol adhesive resins is typically between 42,000-49,000 yuan / ton, with high-purity resorcinol adhesive resins being even more expensive.

[0004] CN103910840A discloses a cashew nut shell bisphenol A (CNBOA) modified resorcinol formaldehyde resin. The method involves mixing resorcinol and cashew nut shell bisphenol A at a weight ratio of 1:0.1 to 1:1, adding an acid catalyst, reacting at 115-130°C for 30-120 minutes, then lowering the temperature to 100°C, and adding an aldehyde compound in a molar ratio of 1:0.5 to 1:0.8 to the resorcinol. After the addition is complete, the mixture is refluxed for 5-30 minutes, then neutralized with sodium hydroxide, and the temperature is raised to 150°C. The mixture is then distilled and dehydrated to obtain the CNBOA-modified resorcinol formaldehyde resin. Modified vulcanized rubber compositions using CNBOA-modified resorcinol formaldehyde resin as a methylene acceptor in an adhesion promoter exhibit better physical properties. A particularly notable improvement is the significantly enhanced extraction performance of steel wire after salt water and steam aging, demonstrating superior steel wire adhesion performance in applications requiring resistance to steam and salt water aging. However, the patent specifies that the mixing weight ratio of resorcinol and cashew nut bicarbonate is 1:0.1 to 1:1. Considering that the cashew nut bicarbonate used in its example has a purity of 40%, the highest substitution rate of cashew nut bicarbonate for resorcinol is only 12.3%. Therefore, it has limited effect on solving the above-mentioned technical problems of resorcinol formaldehyde resin.

[0005] CN 105623188A discloses a cashew nut shell modified phenolic resin and its application as an adhesion promoter in rubber and its products. The cashew nut shell modified phenolic resin in this patent can be prepared by two methods: one method involves reacting cashew nut shell with phenol and formaldehyde in the presence of a catalyst, in which the double bonds of the cashew nut shell alkyl chain are retained in the resin prepared by this method; the other method involves first preparing a resin from phenolic and aldehyde compounds in the presence of a catalyst, and then reacting cashew nut shell with this resin through an alkylation reaction of the double bonds to prepare the cashew nut shell modified phenolic resin, in which the double bonds of the cashew nut shell alkyl chain are significantly consumed. The cashew nut shell modified phenolic resin, as an adhesion promoter, enables the prepared rubber and its products to exhibit characteristics such as no smoke generation during mixing, high modulus, high hardness, and good steel cord extraction performance. However, this method uses refined cashew nut shell as a raw material, resulting in relatively high production costs.

[0006] Crude cashew phenol is a product of decarboxylation treatment of cashew shell oil (a natural oil obtained by dry pressing of cashew shells, whose main component is pentadecyl salicylic acid). It is a viscous black liquid, with cashew phenol as its main chemical component, and also contains 10-20 wt% cardiotonic phenol (i.e., cashew diol) and a small amount of 2-methyl cardiotonic phenol and other impurities. If the crude cashew phenol is further distilled and purified to remove impurities, high-purity refined cashew phenol can be obtained. If cashew oil can be used directly as a raw material to prepare phenolic resins suitable for use as rubber bonding accelerators, it will not only be green and sustainable, but also significantly reduce production costs.

[0007] Therefore, it is of great significance to prepare a phenolic resin suitable for use as a rubber bonding accelerator by directly reacting crude cashew oil with formaldehyde. Summary of the Invention

[0008] Based on the above, the primary technical problem to be solved by the present invention is to provide a cashew phenolic resin prepared from crude cashew phenol and paraformaldehyde as raw materials. It uses non-grain bio-based raw materials, is green and environmentally friendly, and has low production costs. The cashew phenolic resin has good adhesive properties and good compatibility with rubber (the double bonds contained in the structure of crude cashew phenol can participate in the rubber vulcanization crosslinking network), which can achieve reliable bonding between rubber and reinforcing materials, especially impregnated canvas.

[0009] The second technical problem to be solved by the present invention is to provide a method for preparing cashew phenolic resin using crude cashew phenol and paraformaldehyde as raw materials, thereby solving the gelation problem that easily occurs during the preparation of cashew phenolic resin.

[0010] The third technical problem to be solved by the present invention is to provide an adhesive accelerator for rubber products, which contains cashew phenolic resin, which is not only green and environmentally friendly and has low production cost, but also can achieve reliable adhesion between rubber and reinforcing materials, especially impregnated canvas.

[0011] The fourth technical problem to be solved by the present invention is to provide a vulcanized rubber composition for rubber products, wherein the adhesive accelerator contained therein enables reliable adhesion between the rubber and the reinforcing material, especially the impregnated canvas.

[0012] The fifth technical problem to be solved by the present invention is to provide a rubber product with good mechanical properties.

[0013] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a cashew phenolic resin, which is obtained by polycondensation reaction of crude cashew phenol and paraformaldehyde in a solvent at room temperature to 65°C under the action of an acid catalyst for at least 4 hours and then separated; the acid catalyst is a sulfuric acid or oxalic acid solution with a concentration of 0.5-2wt%, and the amount added is 1-4% of the mass of crude cashew phenol.

[0014] For the preparation of cashew phenolic resin of the present invention, since crude cashew phenol contains both cashew phenol and cardiotonic phenol, and the two have different reactivity with formaldehyde, if the reaction temperature has a large influence, a higher temperature will greatly increase the activity of cardiotonic phenol in crude cashew phenol, and the reaction will crosslink rapidly. Therefore, the reaction temperature needs to be controlled below 65°C; while a lower temperature will greatly increase the reaction time. Therefore, as a preferred option, the polycondensation reaction temperature is 55-65°C, more preferably 57-63°C.

[0015] In the preparation of the cashew phenolic resin of this invention, the reaction time affects the molecular weight of the polycondensation product, which in turn affects its subsequent application performance. When the reaction temperature is between room temperature and 65°C, the reaction time generally needs to be at least 4 hours. It is understood that at lower reaction temperatures, the reaction time needs to be extended. Preferably, the polycondensation reaction temperature is 55-65°C, and the reaction time is 4-6 hours, more preferably 5 hours.

[0016] In the preparation of the cashew phenolic resin of this invention, the acid catalyst and its dosage also affect the molecular weight of the polycondensation product, which will have a certain impact on the subsequent application performance. Taking into account both cost and catalytic performance, the acid catalyst is sulfuric acid with a concentration of 1 wt%, and its addition amount is 2-4% of the mass of cashew phenol, more preferably 3%.

[0017] In the preparation of the cashew phenolic resin of the present invention, the molar ratio of crude cashew phenol to paraformaldehyde is usually 1:0.6-0.8, preferably 1:0.8, wherein the molecular weights of crude cashew phenol and paraformaldehyde are 300 g / mol and 30 g / mol, respectively.

[0018] In the preparation of the cashew phenolic resin of the present invention, the solvent is preferably ethanol. More preferably, the amount of ethanol added is 80-150 g / mol based on the molar amount of crude cashew phenol.

[0019] In the preparation of the cashew phenolic resin of the present invention, after the polycondensation reaction is completed, the solvent and the generated water are removed by vacuum distillation to obtain the cashew phenolic resin.

[0020] Since the crude cashew phenol itself is a mixture whose main components are cashew phenol and cardiotonic phenol, the cashew phenol-formaldehyde resin obtained by this invention is also a mixture, wherein the structural formula of the main components is shown below:

[0021] In each structural unit, R is C. 15 H 31-2m m = 0, 1, 2 or 3.

[0022] Secondly, the present invention provides a method for preparing the cashew phenolic resin described in the first aspect, comprising the following steps: adding crude cashew phenol, paraformaldehyde, an acid catalyst, and a solvent into a reaction vessel; controlling the temperature between room temperature and 65°C and stirring to maintain the temperature for at least 4 hours; and separating the cashew phenolic resin after the reaction is completed; the acid catalyst is preferably a 0.5-2% sulfuric acid or oxalic acid solution, and its addition amount is 1-4% of the mass of the crude cashew phenol. The reaction equation is as follows:

[0023] In each structural unit, R is C. 15 H 31-2m m = 0, 1, 2 or 3.

[0024] Preferably, the reaction temperature is between room temperature and 65°C, and the reaction time is at least 4 hours. More preferably, the polycondensation reaction temperature is 55-65°C, more preferably 57-63°C. Even more preferably, the reaction time is 4-6 hours. The present invention particularly prefers a polycondensation reaction temperature of 57-63°C and a reaction time of 5 hours.

[0025] Preferably, the acid catalyst is sulfuric acid with a concentration of 1 wt%, and its addition amount is 2-4% of the mass of crude cashew phenol, more preferably 3%.

[0026] Preferably, the molar ratio of crude cashew phenol to paraformaldehyde is typically 1:0.6-0.8, more preferably 1:0.8, wherein the molecular weights of crude cashew phenol and paraformaldehyde are 300 g / mol and 30 g / mol, respectively.

[0027] In the preparation of the cashew phenolic resin of this invention, the acid catalyst and its dosage also affect the molecular weight of the polycondensation product, which in turn affects its subsequent application performance. Considering both cost and catalytic performance, the acid catalyst is preferably a 0.5-2% sulfuric acid or oxalic acid solution, added at 1-4% of the mass of the crude cashew phenol. More preferably, the acid catalyst is 1 wt% sulfuric acid, added at 2-4% of the mass of the crude cashew phenol, and more preferably 3%.

[0028] In the preparation of the cashew phenolic resin of the present invention, the molar ratio of crude cashew phenol to paraformaldehyde is usually 1:0.6-0.8, preferably 1:0.8, wherein the molecular weights of crude cashew phenol and paraformaldehyde are 300 g / mol and 30 g / mol, respectively.

[0029] In the preparation of the cashew phenolic resin of the present invention, the solvent is preferably ethanol. More preferably, the amount of ethanol added is 80-150 g / mol based on the molar amount of crude cashew phenol.

[0030] Preferably, the solvent is ethanol, and the amount of ethanol added is 80-150 g / mol based on the molar amount of crude cashew phenol.

[0031] In the preparation of the cashew phenolic resin of the present invention, after the polycondensation reaction is completed, the solvent and the generated water are removed by vacuum distillation to obtain the cashew phenolic resin.

[0032] Thirdly, the present invention provides an adhesion promoter for rubber products, comprising a methylene acceptor and a methylene donor, wherein the methylene acceptor is the cashew phenolic resin described in the first aspect.

[0033] The rubber products described in this invention refer to conveyor belts, tires, and other rubber products that require reinforcing materials such as steel wire and polymer fibers as skeleton materials, especially rubber products using dipped canvas as the skeleton material. In some embodiments, the dipped canvas is EP dipped canvas, such as the EP200, EP300, and EP400 models produced by Shuangjian Co., Ltd.

[0034] In some embodiments, the methylene donor is selected from any one or any combination of two or more of hexamethylenetetramine (HMT), hexamethoxymethylmelamine (HMMM), pentamethoxymethylmelamine (PMMM), hexaethoxymethylmelamine, esterified hydroxymethylmelamine, 2-nitro-2-methyl-1-propanol (NMP), and formaldehyde polymers. Preferably, the methylene donor is selected from hexamethoxymethylmelamine (HMMM).

[0035] In a preferred embodiment, the methylene donor is selected from hexamethoxymethyl melamine (HMMM), and the mass ratio of cashew phenolic resin to hexamethoxymethyl melamine is 1-3:5-10, more preferably 1-2:7-8, and most preferably 2:7.5.

[0036] Fourthly, the present invention provides a vulcanized rubber composition for use in rubber articles, comprising the adhesion promoter described in the third aspect.

[0037] The vulcanized rubber composition of this invention includes unsaturated rubber, reinforcing filler, vulcanization system additives, adhesion accelerators, and antioxidants. The unsaturated rubber can be at least one of natural rubber (NR), styrene-butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), chloroprene rubber (CR), nitrile rubber (NBR), butyl rubber (IIR), and ethylene propylene diene monomer (EPDM). The reinforcing filler can be carbon black, silica, etc. The vulcanization system additives include vulcanizing agents, vulcanization accelerators, and vulcanization activators. The vulcanizing agent can be sulfur. The vulcanization accelerator can be a thiophene accelerator, such as 2-mercaptobenzothiazole (M) or dibenzothiazole disulfide (DM); or a sulfenamide accelerator, such as N-cyclohexyl-2-benzothiazole sulfenamide (CZ) or N-oxoethylene-2-benzothiazole sulfenamide (NOBS). The vulcanization activator can be at least one of metal oxides (such as zinc oxide, used in combination with stearic acid), fatty acids (such as stearic acid, oleic acid, lauric acid, etc.), and metal soaps (such as cobalt stearate, zinc stearate, etc.). The antioxidant can be at least one of antioxidant 4020, antioxidant 4010, antioxidant RD, etc. Typically, in the vulcanized rubber composition, the amount of reinforcing filler is 45-55% of the mass of the unsaturated rubber, the amount of vulcanization system additives is 5-20% of the mass of the unsaturated rubber, the amount of antioxidant is 1-5% of the mass of the unsaturated rubber, and the amount of adhesion accelerator is 6-13% of the mass of the unsaturated rubber.

[0038] In some embodiments, the unsaturated rubber is a combination of natural rubber and styrene-butadiene rubber, with a mass ratio of 40-60%:60-40%; the reinforcing filler is composed of carbon black and silica; the vulcanization system additives are composed of sulfur, stearic acid, zinc oxide, cobalt stearate, and accelerator CZ; the adhesion accelerator is composed of cashew phenolic resin and hexamethoxymethyl melamine resin; and the antioxidant is antioxidant 4020; the carbon black, silica, sulfur, stearic acid, zinc oxide, cobalt stearate, accelerator CZ, cashew phenolic resin, hexamethoxymethyl melamine resin, and antioxidant 4020 account for 40-55%, 7-8%, 2-4%, 1-2%, 5-10%, 1-2%, 1-2%, 1-3%, 5-10%, and 1-2% of the mass of the unsaturated rubber, respectively.

[0039] Fifthly, the present invention provides a rubber article obtained by hot-pressing vulcanization of a layered material, the layered material comprising alternating layers of compounded rubber sheets and EP-impregnated canvas, the layered material comprising at least one layer of compounded rubber sheet and at least two layers of EP-impregnated canvas; the compounded rubber sheet is obtained by compounding the vulcanized rubber composition described in the fifth aspect.

[0040] The preparation method of the compounded rubber sheet according to the present invention generally involves: weighing each raw material, melting and mixing them, mixing them evenly to obtain a compounded rubber, and then extruding the mixture to obtain a compounded rubber sheet. In some embodiments, the compounded rubber sheet is prepared in a two-roll mill, with the temperature of the front and rear rolls of the two-roll mill set at 60~70℃.

[0041] The hot-press vulcanization described in this invention is carried out on a flat vulcanizing machine at a vulcanization temperature of 140-160℃ and a pressure of 14-16 MPa. The vulcanization time depends on the thickness of the sample.

[0042] The rubber products prepared by this invention can be used in the field of rubber conveyor belts.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Compared to industrial-grade resorcinol phenolic resin, the cashew phenolic resin preparation method of the present invention, using crude cashew phenol as a phenolic raw material, is not only green and sustainable, but also significantly reduces production costs (the price of industrial-grade resorcinol phenolic resin is approximately RMB 42,000-49,000 / ton, while high-purity resorcinol reaches RMB 50,000-60,000 / ton; the cost of the cashew phenolic resin prepared by the present invention can be reduced to RMB 4,450-6,000 / ton). It also solves the problem of fuming during the production process of resorcinol, reducing harm to the human body. The preparation method of the present invention, through optimization of reaction conditions, solves the problem of easy gelation of crude cashew phenol during the preparation of phenolic resin. It is simple to operate, has mild reaction conditions, and is easy to industrialize. The cashew phenolic resin of the present invention achieves bonding performance comparable to that of industrial-grade resorcinol phenolic resin in the adhesion between reinforced rubber and reinforcing materials (such as impregnated canvas). Rubber products using cashew phenolic resin as an adhesive accelerator and methylene receptor as a binder exhibit mechanical properties that are no less than, or even better than, those using resorcinol phenolic resin as an adhesive accelerator and methylene receptor as a binder.

[0044] (2) Compared with existing cashew phenol-modified phenolic resins, the present invention achieves a 100% bio-based raw material substitution rate, and the cashew phenolic resin of the present invention achieves better bonding performance than cashew phenol-modified phenolic resins in the bonding between reinforced rubber and reinforcing materials (such as impregnated canvas).

[0045] (3) Compared with existing resorcinol aldehyde resins modified with cashew nut shell phenol, the present invention achieves a 100% bio-based raw material substitution rate, solves the problem of fuming during the production process of resorcinol, and reduces harm to the human body. Moreover, the cashew nut shell phenolic resin of the present invention achieves better bonding performance than cashew nut shell phenolic resins in the adhesion between reinforced rubber and reinforcing materials (such as impregnated canvas). Detailed Implementation

[0046] The technical solution of the present invention will be further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0047] Unless otherwise specified in the embodiments of this invention, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained through conventional technical means or commercially available.

[0048] Crude cashew phenol (approximately 87% cashew phenol by mass, 11% cardiotonic phenol by mass, and approximately 1.4% 2-methylcardiotonic phenol by mass, with the remainder being impurities), paraformaldehyde, sulfuric acid, sodium hydroxide, ethanol, natural rubber (Vietnam rubber 3L), styrene-butadiene rubber (1502 Shanghai Zhengshang Chemical Technology Co., Ltd.), and various additives were all provided by Jiangsu Union Chemical Co., Ltd. EP-impregnated canvas and commonly available methylene acceptors were provided by Shuangjian Co., Ltd. There are three models of EP-impregnated canvas: EP200, EP300, and EP400. The resorcinol phenolic resin provided by Shuangjian Co., Ltd. is model SL-3017.

[0049] In the embodiments of this invention, the quantities mentioned are all by weight.

[0050] Example 1: Preparation of cashew phenolic resin

[0051] Sample 1: Crude cashew nut shellac, paraformaldehyde, catalyst, and an appropriate amount of ethanol were poured into a three-necked flask. The molar ratio of crude cashew nut shellac (300 g / mol) to paraformaldehyde was 1:0.8. The catalyst was a 1 wt% sulfuric acid solution, added at 3.0% of the crude cashew nut shellac content. The ethanol content was 100 g per 1 mol of phenol. The temperature was gradually raised to 60℃ with stirring, and the reaction was maintained at 60±3℃ for 5 h. Then, vacuum distillation was carried out at the same temperature to obtain cashew nut shellac phenolic resin.

[0052] Sample 2: The preparation method is the same as Sample 1, except that the reaction time is shortened to 4 h, while the other conditions remain unchanged; Sample 3: The preparation method is the same as that of Sample 1, except that the reaction time is extended to 6 h, while the other conditions remain unchanged; Sample 4: The preparation method is the same as Sample 1, except that the amount of catalyst added is reduced to 2.0 wt% of the amount of crude cashew phenol added, while the other conditions remain unchanged; Sample 5: The preparation method is the same as Sample 1, except that the amount of catalyst added is increased to 4.0 wt% of the amount of crude cashew phenol added, and the other conditions remain unchanged.

[0053] Sample 6: The preparation method is the same as Sample 1, except that the catalyst concentration is changed to 0.5%, while the amount added remains the same.

[0054] Sample 7: The preparation method is the same as Sample 1, except that the catalyst concentration is changed to 2%, while the amount added remains the same.

[0055] Sample 8: The preparation method is the same as Sample 1, except that the catalyst is replaced with oxalic acid, while the concentration and amount added remain the same.

[0056] Sample 9: The preparation method is the same as Sample 1, except that crude cashew phenol is replaced with refined cashew phenol, and all other conditions remain the same.

[0057] Sample 10 (refer to the example in CN103910840A): 110 g of resorcinol was weighed and added to a 500 ml four-necked flask equipped with a spherical condenser. The mixture was heated to 115-125°C and stirred until melted. 55 g of cashew nut shell glycoside (40% purity) was added and stirred, followed by 0.35 g of p-toluenesulfonic acid. The reaction was allowed to proceed for 60 min, then cooled to approximately 100°C. A 37 wt% formaldehyde aqueous solution (containing 46.6 g of formaldehyde) was added dropwise. After the formaldehyde addition was complete, the mixture was refluxed, and reflux was continued. Finally, the mixture was neutralized with 0.18 g of 50% sodium hydroxide solution. The mixture was then heated to 140°C and distilled under normal and reduced pressure. Cashew nut shell glycoside-modified resorcinol aldehyde resin was obtained.

[0058] Sample 11 (refer to Example 1 of CN 105623188A): In a 5L four-necked round-bottom reaction flask equipped with a stirrer, thermometer, reflux condenser and dropping funnel, 1880g of phenol, 235g of refined cashew phenol and 25g of oxalic acid were added. The mixture was heated to 95-100°C, and then 1260g of 37% formaldehyde aqueous solution was added dropwise over 90 minutes. After the addition was completed, the mixture was refluxed for another 30 minutes. At this time, the reflux device was changed to a distillation device, and the temperature was raised to distill off the water and some unreacted phenol generated in the reaction. When the temperature reached 114-115°C, no more water was distilled off. The temperature was raised to 195-200°C, and steam was introduced for distillation for another 60 minutes. Then, the mixture was distilled under reduced pressure at 195-200°C for another 60 minutes (vacuum degree -95KPa). After the vacuum was broken, cashew phenol modified phenolic resin was obtained.

[0059] Example 2

[0060] A rubber compounding formula, made from the following raw materials:

[0061] The preparation method of rubber products is carried out according to the following steps: Rubber mixing was performed using an open-type mixing mill (Qingdao Kegao Rubber & Plastic Machinery Technology Equipment Co., Ltd., XK160). The temperature of both the front and rear rolls was 65℃, and the roll gap was adjusted to approximately 1.2 mm. First, NR and SBR were mixed for 5 minutes until the mixture wrapped around the rolls. Then, Sample 1 prepared in Example 0 was added and mixed for 2-3 minutes until homogeneous. Carbon black, silica, and stearic acid were then added. After mixing for 10 minutes until homogeneous, zinc oxide, HMMM, antioxidant 4020, accelerator CZ, and cobalt stearate were added. After mixing for 8 minutes until homogeneous, sulfur was added. Finally, the mixture was rolled in a triangular pattern ten times and then sheeted. The entire process took approximately 30 minutes.

[0062] The rubber compound was pressed into sheets of approximately 5 mm thickness. These sheets were then layered with EP-impregnated canvas to create a layered material. The EP-impregnated canvas consisted of four layers: rubber compound-EP-impregnated canvas-rubber compound-EP-impregnated canvas-rubber compound-EP-impregnated canvas-rubber compound-EP-impregnated canvas-rubber compound. EP200 EP-impregnated canvas was used. The sample's width and length were 15 cm and 20 cm, respectively. The temperature of the flat vulcanizing apparatus was set to 150℃, the vulcanization time to 20 min, and the pressure to 15 MPa to obtain the rubber product.

[0063] Example 3

[0064] Rubber products were prepared according to the method of Example 2, the only difference being that EP300 was used for the EP impregnated canvas.

[0065] Example 4

[0066] Rubber products were prepared according to the method of Example 2, the only difference being that EP400 was used for the EP impregnated canvas.

[0067] Example 5

[0068] Rubber products were prepared according to the method of Example 2, except that the addition amount of Sample 1 was changed to 1 phr, and EP200 was used for the EP impregnated canvas.

[0069] Example 6

[0070] Rubber products were prepared according to the method of Example 2, except that the addition amount of Sample 1 was changed to 3 phr, and EP200 was used for the EP impregnated canvas.

[0071] Example 7

[0072] Rubber products were prepared according to the method of Example 2, except that: Sample 1 was replaced with Sample 2, and EP-impregnated canvas was used as EP200.

[0073] Example 8

[0074] Rubber products were prepared according to the method of Example 2, except that: Sample 1 was replaced with Sample 3, and EP200 was used for the EP-impregnated canvas.

[0075] Example 9

[0076] Rubber products were prepared according to the method of Example 2, except that: Sample 1 was replaced with Sample 4, and EP200 was used for the EP-impregnated canvas.

[0077] Example 10

[0078] Rubber products were prepared according to the method of Example 2, except that: Sample 1 was replaced with Sample 5, and EP200 was used for the EP-impregnated canvas.

[0079] Example 11

[0080] Rubber products were prepared according to the method of Example 2, except that: Sample 1 was replaced with Sample 6, and EP200 was used for the EP-impregnated canvas.

[0081] Example 12

[0082] Rubber products were prepared according to the method of Example 2, except that: Sample 1 was replaced with Sample 7, and EP200 was used for the EP-impregnated canvas.

[0083] Example 13

[0084] Rubber products were prepared according to the method of Example 2, except that: Sample 1 was replaced with Sample 8, and EP200 was used for the EP-impregnated canvas.

[0085] Comparative Example 1

[0086] Rubber products were prepared according to the method of Example 2, except that: Sample 1 was replaced with Sample 9, and EP200 was used for the EP-impregnated canvas.

[0087] Comparative Example 2

[0088] Rubber products were prepared according to the method of Example 2, except that: Sample 1 was replaced with Sample 10, and EP200 was used for the EP-impregnated canvas.

[0089] Comparative Example 3

[0090] Rubber products were prepared according to the method of Example 2, with the only difference being that: Sample 1 was replaced with resorcinol phenolic resin SL-3017 provided by Shuangjian Co., Ltd., and EP-impregnated canvas was EP200.

[0091] Comparative Example 4

[0092] Rubber products were prepared according to the method of Example 2, with the only difference being that: Sample 1 was replaced with resorcinol phenolic resin SL-3017 provided by Shuangjian Co., Ltd., and EP impregnated canvas was EP300.

[0093] Comparative Example 5

[0094] Rubber products were prepared according to the method of Example 2, with the only difference being that: Sample 1 was replaced with resorcinol phenolic resin SL-3017 provided by Shuangjian Co., Ltd., and EP impregnated canvas was EP400.

[0095] Comparative Example 6: Rubber products were prepared according to the method of Example 2, except that: Sample 1 was replaced with Sample 11, and EP-impregnated canvas was EP200.

[0096] Comparative Example 7

[0097] Rubber products were prepared according to the method of Example 2, except that the reaction temperature was increased to 75°C and the reaction time was 2 hours, at which point the reaction gelled and the reaction failed.

[0098] Comparative Example 8

[0099] Rubber products were prepared according to the method of Example 2, except that the reaction temperature was increased to 90°C and the reaction time was 0.5 h, at which point the reaction gelled and the reaction failed.

[0100] Application evaluation process: The materials obtained in each embodiment and comparative example were subjected to the following tests, and the test methods are as follows: 1. Peel strength test: Using rubber products as test samples, according to GB / T32109—2015, the test samples are cut into long strips with a width of 25 mm and a length of more than 15 cm. A cut of about 5 cm deep is made between every two pieces of EP-impregnated canvas, resulting in three cuts, which are recorded as cut 1-2, cut 2-3, and cut 3-4. The peel strength is tested using a universal testing machine controlled by Jiangsu Qiantong (QT-6201S). The moving speed of the tensile testing motorized clamp is set to (100±10) mm / min. Three data points can be obtained for each strip, and at least three strips are required for each sample. The ratio of peel strength to sample width is the adhesive peel strength of the sample. The arithmetic mean of the three samples is taken as the test result of the adhesive peel strength, expressed in Newtons per millimeter (N / mm). The value is rounded to one decimal place according to the rules given in GB / T8170. The experimental results are shown in Table 1.

[0101] Table 1 Peel strength test results

[0102] The best data from the three sets of data for each sample was used as the data to measure the peel strength of the sample. According to the results in Table 1, the peel strength of Examples 2 and 4 was significantly higher than that of Comparative Examples 3 and 5, respectively. The peel strength of Examples 3 and Comparative Example 4 was comparable. It can be concluded that, under the same EP-impregnated canvas conditions, the effect of cashew phenolic resin as a methylene acceptor is no less than or better than that of resorcinol phenolic resin. Examples 2, 5, and 6 added different parts of cashew phenolic resin under the same EP-impregnated canvas conditions. It can be clearly seen that the more parts of cashew phenolic resin added, the stronger the peel strength. Examples 7-13 changed the preparation conditions of cashew phenolic resin. Compared with Example 2, the effect of the obtained cashew phenolic resin as a methylene acceptor was slightly reduced, but it was still better than that of Comparative Example 3. Comparative Example 1 and Example 2 used phenolic resin prepared by refined cashew phenol and phenolic resin prepared by crude cashew phenol, respectively. The latter not only significantly reduced the preparation cost, but also had a better adhesive effect. The cashew nut shell phenol-modified resorcinol aldehyde resin in Comparative Example 2 has a low bio-substitution rate, still suffers from high production costs and health and environmental problems associated with resorcinol, and its adhesive effect is significantly inferior to that of Example 2. The cashew nut shell phenol-modified aldehyde resin in Comparative Example 6 also exhibits significantly inferior adhesive effect compared to Example 2.

[0103] 2. Mechanical property testing: Rubber products were used as test samples. Mechanical properties of the samples were tested according to GB / T 1040.1 2006 on a universal testing machine controlled by Jiangsu Qiantong (QT-6201S). The elongation at break (EB, %) and tensile strength (TS, MPa) of the samples were obtained. The samples were type 5A, with a clamp spacing of 30 mm and a tensile speed of 50 mm / min. 3-5 samples were prepared for testing per group, and the average value was taken. Error was calculated. Blank samples were those without any added methylene acceptors. The experimental results are shown in Table 2.

[0104] Table 2 Comparison of Mechanical Performance Test Results

[0105] According to the results in Table 2, compared with the blank control, the tensile strength of rubber was generally improved after the addition of methylene acceptors, but the elongation at break was generally decreased. The tensile strength was positively correlated with the amount of methylene acceptors added, while the elongation at break was negatively correlated with the amount of methylene acceptors added. The tensile strength of Comparative Example 3 was slightly lower than that of Example 2.

[0106] 3. Hardness & Density Test: Rubber products were used as test samples. Hardness was tested on a Type A hardness tester (HLX-AC type) according to GB / T 2411-2008. Five hardness values ​​were measured on the same sample, and their average value was calculated. Density was tested on an electronic densitometer (FK-120DT type) using the immersion method according to GB / T 1033.1-2008. Five density values ​​were measured on the same sample, and their average value was calculated. A blank control was a sample without any added methylene acceptors. The experimental results are shown in Table 3.

[0107] Table 3 Comparison of Hardness & Density Test Results

[0108] According to the results in Table 3, the hardness and density of Examples 2, 5, and 6 were higher than those of the blank control and similar to those of Comparative Example 3.

[0109] 4. Vulcanization curve test: Layered materials were used as test samples. The vulcanization performance was tested using a high-speed ferrosulfide analyzer, referring to the standards GB / T16584-1996 and GB / T1233-2008, under conditions of 150℃, 1° radian, and 1.67 Hz. The experimental results are shown in Table 4.

[0110] Table 4 Comparison of vulcanization performance test results

[0111] It can be seen that with the increase of the amount of methylene acceptor added, the ML and MH of the rubber both increased, and the vulcanization curve shifted to the right, that is, tc10 and tc90 were lengthened; the ML and MH of Comparative Example 3 were slightly higher than those of Example 1, while tc10 and tc90 were lower than those of Example 1.

[0112] 5. Mooney viscosity test: The compounded film was used as the test sample. The Mooney viscosity was tested using a Suzhou Qiantong MV2-2000 intelligent computer-controlled Mooney viscometer. The test was conducted at 100℃ for 4 min, with a preheating time of 1 min, under the condition of a large rotor. The experimental results are shown in Table 5.

[0113] Table 5 Comparison of Mooney viscosity test results

[0114] It can be seen that Mooney viscosity is positively correlated with the amount of methylene acceptor added. The Mooney viscosity of Example 6 is slightly greater than that of Comparative Example 3, while the Mooney viscosity of Examples 2 and 5 is less than that of Comparative Example 3. This is because both cashew phenol and cardiotonic phenol have long carbon chains, which have a certain plasticizing effect.

[0115] The scope of the present invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of the present invention, and all such modifications and variations should fall within the scope of the present invention.

Claims

1. A cashew phenolic resin, characterized in that: The cashew phenolic resin is obtained by polycondensation reaction of crude cashew phenol and paraformaldehyde in a solvent at room temperature to 65°C under the action of an acid catalyst for at least 4 hours, followed by separation. The acid catalyst is a sulfuric acid or oxalic acid solution with a concentration of 0.5-2wt%, and its addition amount is 1-4% of the mass of crude cashew phenol.

2. The cashew phenolic resin as described in claim 1, characterized in that: The polycondensation reaction temperature is 55-65℃, and the reaction time is 4-6h; preferably, the polycondensation reaction temperature is 57-63℃, and the reaction time is 5h.

3. The cashew phenolic resin as described in claim 1, characterized in that: The acid catalyst is sulfuric acid with a concentration of 1 wt%, and its addition amount is 2-4% of the mass of cashew phenol, preferably 3%.

4. The cashew phenolic resin as described in claim 1, characterized in that: The molar ratio of crude cashew phenol to paraformaldehyde is 1:0.6-0.8, preferably 1:0.8, wherein the molecular weights of crude cashew phenol and paraformaldehyde are 300 g / mol and 30 g / mol, respectively.

5. The cashew phenolic resin as described in claim 1, characterized in that: The solvent is ethanol.

6. A method for preparing cashew phenolic resin as described in any one of claims 1-5, characterized in that: The preparation method includes the following steps: crude cashew phenol, paraformaldehyde, acid catalyst and solvent are added to a reaction vessel, the temperature is controlled between room temperature and 65°C and stirring is turned on to keep the reaction at a temperature of at least 4 hours, and cashew phenol-formaldehyde resin is obtained after the reaction is completed; the acid catalyst is preferably a sulfuric acid or oxalic acid solution with a concentration of 0.5-2%, and its addition amount is 1-4% of the mass of crude cashew phenol.

7. An adhesion promoter for rubber products, comprising a methylene acceptor and a methylene donor, characterized in that: The methylene receptor is cashew phenolic resin as described in any one of claims 1-5.

8. The adhesion promoter for rubber products as described in claim 7, characterized in that: The methylene donor is selected from any one or any combination of two or more of hexamethylenetetramine, hexamethoxymethyl melamine, pentamethoxymethyl melamine, hexaethoxymethyl melamine, esterified hydroxymethyl melamine, 2-nitro-2-methyl-1-propanol, and formaldehyde polymers.

9. A vulcanized rubber composition for use in rubber products, characterized in that: The vulcanized rubber composition for use in rubber articles includes the adhesion promoter as described in claim 7 or 8.

10. A rubber product obtained by hot-pressing and vulcanizing a layered material, said layered material comprising alternating layers of compounded rubber sheets and EP-impregnated canvas, the layered material comprising at least two layers of compounded rubber sheets and at least one layer of EP-impregnated canvas; characterized in that: The compounded rubber sheet is obtained by compounding the vulcanized rubber composition according to claim 9.

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