Ammonia-free halogen-free high-flame-retardant phenolic moulding plastic and preparation method thereof

Abstract

The invention provides an ammonia-free halogen-free high-flame-retardant phenolic moulding plastic. The ammonia-free halogen-free high-flame-retardant phenolic moulding plastic is prepared from the following raw materials: dimethylene ether type thermosetting phenolic resin, hydroxymethyl type thermosetting phenolic resin, bisphenol F phenolic resin, cellulose, glass fibers, a flame retardant, a curing accelerator and a release agent. The invention also provides a preparation method of the ammonia-free halogen-free high-flame-retardant phenolic moulding plastic. The prepared and molded product is ammonia-free and halogen-free, has the advantages of high flame retardance, high temperature resistance, good mechanical strength and excellent electrical performance, and can meet the requirements of high-end electronic and electric appliance accessory materials.

Description

Technical Field

[0001] The invention belongs to the technical field of composite materials, and in particular relates to an ammonia-free and halogen-free highly flame-retardant phenolic molding compound and a preparation method thereof. Background Art

[0002] Phenolic molding compound is one of the three major thermosetting plastics. It has low cost and wide application, especially suitable for household appliances, electrical accessories and mechanical accessories. General phenolic molding compound is generally made of phenolic resin as a binder, wood powder and minerals as fillers, and a curing agent and accelerator. Ordinary phenolic molding compound is based on thermoplastic phenolic resin. Since thermoplastic phenolic resin only melts but does not solidify when heated, hexamethylenetetramine (urotropine) is generally added as a curing agent. During heating and curing, a small amount of ammonia produced by the decomposition of urotropine will remain in the product in the form of free ammonia, and will be slowly released during the use of the product. Under normal circumstances, these trace amounts of ammonia will not affect the use of the product, but in the field of electrical appliances, even if the amount of ammonia is very small, after a long period of contact, it will still corrode the metal parts in the electrical appliance, resulting in problems such as poor contact, affecting the safety and reliability of instruments and meters, and reducing the service life of the electrical appliance. Moreover, in terms of electrical properties, the PTI of phenolic molding compounds can generally only reach 175, which also affects the scope of use of phenolic molding compounds. With the development of high-end electronic and electrical industries, requirements for comprehensive properties such as ammonia-free, halogen-free and high flame retardancy have been put forward.

[0003] Therefore, the relevant technical personnel of our company have done a lot of research and development and improvement work in view of the comprehensive performance requirements of the material, such as ammonia-free and halogen-free, high flame retardancy, high temperature resistance, mechanical strength and electrical properties.

[0004] The applicant of the present invention has made continuous and unremitting efforts to use dimethyl ether type thermosetting phenolic resin, hydroxymethyl type thermosetting phenolic resin and bisphenol F phenolic resin as adhesives, cellulose and glass fiber as reinforcing fibers, and flame retardants, curing accelerators, and release agents, so that the products after the materials are formed are ammonia-free and halogen-free, have high flame retardancy, high temperature resistance, good mechanical strength, and excellent electrical properties. It is suitable for the requirements of high-end electronic and electrical accessories materials. Summary of the invention

[0005] In view of the defects of the prior art, the object of the present invention is to provide an ammonia-free and halogen-free highly flame-retardant phenolic molding compound with easily available raw materials, easy processing and excellent performance, and a preparation method thereof.

[0006] To achieve the above purpose, the solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides an ammonia-free, halogen-free, highly flame-retardant phenolic molding compound, comprising the following raw materials in percentage by weight:

[0008]

[0009] Preferably, the preparation method of the dimethyl ether type thermosetting phenolic resin comprises the following steps: adding phenol and formaldehyde in a certain molar ratio into a reaction kettle equipped with a reflux condenser, a stirrer, a heating device and a dehydration device; then adding zinc acetate in an amount of 0.5%-2% of the total feed amount to the reaction mixture, and adjusting the pH value to 4.5-5.0; then heating to 80-90°C, reflux reaction for 2-3 hours, and then reducing pressure and dehydrating; finally, the temperature is raised to 130°C to remove phenol until the desired softening point is reached to obtain the dimethyl ether type thermosetting phenolic resin (solid); the molar ratio of phenol to formaldehyde is 1: (1.4-1.5), the softening point is 70-75°C, the free phenol is ≤5.5, and the polymerization rate is 120-180S.

[0010] Preferably, the preparation method of the hydroxymethyl type thermosetting phenolic resin comprises the following steps: phenol and formaldehyde (F) are charged into a reaction kettle equipped with a reflux condenser, a stirrer, a heating device and a dehydration device according to a certain ratio; then, a liquid alkali with a mass percentage concentration of 50% is added to the reaction mixture, the pH value in the reaction system is adjusted to 9.0, the reaction temperature is controlled at 65-68°C, and the reaction is carried out for 1 hour; then the temperature is raised to 78-80°C for reflux reaction for 1.5 hours; cooled to 50°C, phosphoric acid is added, the pH value is adjusted to 7.0-7.1, and then the vacuum degree is gradually increased to above -0.095Mpa for dehydration, and finally the temperature is raised to 98°C to remove phenol until the desired softening point is reached, and finally the hydroxymethyl type thermosetting phenolic resin is obtained; the molar ratio of phenol to formaldehyde is 1:(1.8-1.9), the softening point is 65-70°C, the free phenol is ≤5.5, and the polymerization rate is 50-90S.

[0011] Preferably, the bisphenol F phenolic resin is a bisphenol F modified phenolic resin, the weight ratio of bisphenol F to phenol is 1:2, the molar ratio of phenol to formaldehyde is 1:(0.78-0.82), free phenol ≤4.5, the softening point is 100-110°C, and the polymerization rate is 90-120S.

[0012] Preferably, the cellulose is purified cellulose from wood fiber or cotton fiber, with a cellulose content of ≥98% and a fineness of 60-200 meshes.

[0013] Preferably, the glass fiber is an alkali-free glass fiber with a diameter of 11-13 μm and a length of 1-5 mm.

[0014] Preferably, the flame retardant is selected from zinc borate and aluminum hydroxide or a mixture of the two.

[0015] Preferably, the curing accelerator is selected from one or more of magnesium oxide, calcium oxide and calcium hydroxide.

[0016] Preferably, the release agent is selected from one or more of calcium stearate, zinc stearate, lithium stearate, stearic acid, stearic acid amide and ethylene bis stearic acid amide.

[0017] In a second aspect, the present invention also provides a method for preparing the ammonia-free and halogen-free highly flame-retardant phenolic molding material as described above, comprising the following steps: firstly ultra-finely grinding dimethyl ether type thermosetting phenolic resin, hydroxymethyl type thermosetting phenolic resin, bisphenol F phenolic resin and curing accelerator to a fineness of more than 200 meshes, then uniformly mixing the above mixture with other raw materials, heating and mixing or extruding, and finally granulating and forming, so as to obtain the ammonia-free and halogen-free highly flame-retardant phenolic molding material.

[0018] According to the present invention, the present invention uses two solid thermosetting phenolic resins, namely, dimethyl ether type thermosetting phenolic resin and hydroxymethyl type thermosetting phenolic resin, in combination with bisphenol F phenolic resin, and then adds fiber fillers, flame retardants, curing accelerators, release agents and other raw materials, and the phenolic molding plastic finally obtained has synergistic heat resistance, mechanical properties and electrical properties. The reason is that: due to the presence of dimethyl ether bond bridging structure in the molecular structure, the dimethyl ether type thermosetting phenolic resin has good toughness, which is beneficial to improve the mechanical strength of the ammonia-free molding plastic; due to the presence of hydroxymethyl functional groups in the molecular structure, the hydroxymethyl type thermosetting phenolic resin has good heat resistance, and the aldehyde ratio (i.e., the molar ratio of formaldehyde to phenol) is high (1.8 to 1.9: 1), thereby increasing the content of hydroxymethyl cross-linking groups, on the one hand, increasing the cross-linking density of the molding plastic, and on the other hand, it can also be used as a curing agent for bisphenol F phenolic resin.

[0019] According to the preparation method of the non-ammonia and non-halogen highly flame-retardant phenolic molding plastic of the present invention, firstly, dimethylene ether type thermosetting phenolic resin, hydroxymethyl type thermosetting phenolic resin, bisphenol F phenolic resin and curing accelerator are ultra-finely crushed to a fineness of more than 200 meshes; then, the above mixture is uniformly mixed with other raw materials, heated and kneaded or extruded, and finally granulated to obtain a granular phenolic molding plastic. Subsequently, the granular phenolic molding plastic is injection molded to obtain a phenolic plastic molded product.

[0020] Since the three phenolic resins are all solid at room temperature, after ultrafine grinding and sufficient mixing at room temperature, the contact area between the three phenolic resins is greatly increased, making the cross-linking reaction of the three phenolic resins in the subsequent phenolic plastic moldings after injection molding more complete during the molding process, thereby improving the mechanical strength and heat resistance of the phenolic molding material.

[0021] Moreover, the softening points of the three solid phenolic resins used in the present invention are all higher than 60° C. The granular phenolic molding material products prepared in the present invention will not cause agglomeration during storage, are convenient to transport, and have strong usability and operability of subsequent products.

[0022] According to the process of forming a phenolic plastic molded product from a granular phenolic molding material prepared by the present invention after subsequent injection molding, the present invention adds a thermoplastic bisphenol F phenolic resin to the raw materials constituting the phenolic molding material in order to improve the thermal rigidity of the phenolic plastic molded product after injection molding (i.e., the rigidity of the molded product when it is ejected from the mold. If only a thermosetting phenolic resin is used, the molded product will have poor thermal rigidity when it is ejected from the mold, become soft, and be easily deformed due to the small molecular weight of the thermosetting phenolic resin). The bisphenol F phenolic resin is used instead of ordinary thermoplastic phenolic resin because the molecular structure of bisphenol F makes the heat resistance of the modified phenolic resin better than that of ordinary phenolic resin, thereby improving the heat resistance and electrical properties of the ammonia-free phenolic molding material.

[0023] According to the present invention, two solid thermosetting phenolic resins, namely, dimethylene ether type thermosetting phenolic resin and hydroxymethyl type thermosetting phenolic resin, are used in combination with thermoplastic bisphenol F phenolic resin, and no hexamethylenetetramine (urotropine) is added as a curing agent. The free ammonia content of the phenolic plastic molded product after injection molding is below 10 ppm, that is, the phenolic plastic molding material is free of free ammonia.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The phenolic molding material provided by the present invention is an ammonia-free material because no methenamine is added as a curing agent. The halogen content in the selected raw materials is strictly controlled, so it is a halogen-free material. The compounded flame retardant is added to make the material have high flame retardancy. The ammonia-free resin system is used and cellulose and glass fiber are used as reinforcing materials, so it has high temperature resistance and excellent mechanical strength and electrical properties. The material is suitable for the requirements of high-end electronic and electrical accessories. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with the embodiments, the purpose of which is to better understand the content of the present invention and embody the essential characteristics of the present invention, so the examples given should not be regarded as limiting the scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the enlightenment of the present invention or by combining the features of the present invention with other prior arts falls within the scope of protection of the present invention.

[0027] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0028] The manufacturing method of the molding material of the present invention can adopt the conventional twin-roller mixing method or the screw extrusion method.

[0029] Before mixing or extruding, the resin binder including dimethylene ether type thermosetting phenolic resin, hydroxymethyl type thermosetting phenolic resin, bisphenol F phenolic resin and curing accelerator are pre-ultra-finely crushed to a fineness of more than 200 meshes, so that the cross-linking reaction between the three phenolic resins is more sufficient, thereby improving the mechanical strength and heat resistance; then the above mixture is evenly mixed with other raw materials, heated and mixed or extruded, and finally granulated to obtain the required product.

[0030] The formulation materials shown in Table 1 are crushed, mixed, kneaded or extruded according to the above-mentioned manufacturing method, and finally granulated and formed to obtain the required product. The formulations and characteristic data of Examples 1-5 are all listed in this table. The formulation amounts in the table are all expressed in weight %.

[0031] The test pieces for property evaluation are prepared by compression molding. The performance indexes are measured according to ISO14526-2 standard. The evaluation method is as follows:

[0032] The molding conditions are: preheating temperature: 100-110°C, pressing mold temperature: 170-175°C, and curing time: 1.0min / mm.

[0033] Table 1

[0034]

[0035] The materials in Table 1 are annotated as follows:

[0036] (1) Dimethylene ether type thermosetting phenolic resin

[0037] The preparation method of dimethyl ether type thermosetting phenolic resin is as follows: phenol and formaldehyde are charged into a reaction kettle equipped with a reflux condenser, a stirrer, a heating device and a dehydration device according to a molar ratio of 1: (1.4-1.5); then 0.5%-2% (e.g. 1%) of zinc acetate in the total feed amount is added to the reaction mixture, and the pH value is adjusted to 4.5-5.0; then the temperature is raised to 80-90° C., refluxed for 2-3 hours, and then the pressure is reduced and dehydrated; finally the temperature is raised to 130° C. to remove phenol until the desired softening point of 70-75° C. is reached to obtain the dimethyl ether type thermosetting phenolic resin (solid).

[0038] Physical properties of dimethylene ether type thermosetting phenolic resin: solid, softening point 70-75°C, molar ratio of phenol to formaldehyde 1:(1.4-1.5), free phenol ≤5.5, polymerization rate 120-180S. The determination of technical indicators of phenolic resin shall be carried out in accordance with GB / T 30772-2014.

[0039] (2) Hydroxymethyl thermosetting phenolic resin

[0040] The preparation method of hydroxymethyl type thermosetting phenolic resin is as follows: phenol and formaldehyde (F) are charged into a reaction kettle equipped with a reflux condenser, a stirrer, a heating device and a dehydration device according to a certain ratio; then, liquid alkali with a mass percentage concentration of 50% is added to the reaction mixture, the pH value in the reaction system is adjusted to 9.0, the reaction temperature is controlled at 65-68°C, and the reaction is carried out for 1 hour; then, the temperature is raised to 78-80°C for reflux reaction for 1.5 hours; cooled to 50°C, phosphoric acid is added, the pH value is adjusted to 7.0-7.1, and then the vacuum degree is gradually increased to above -0.095MPa for dehydration, and finally the temperature is raised to 98°C to remove phenol until the desired softening point is reached, and finally the hydroxymethyl type thermosetting phenolic resin is obtained.

[0041] The physical properties of hydroxymethyl thermosetting phenolic resin are as follows: solid, softening point 65-70°C, molar ratio of phenol to formaldehyde 1:(1.8-1.9), free phenol ≤5.5, polymerization rate 50-90S. The determination of technical indicators of phenolic resin shall be carried out in accordance with GB / T30772-2014.

[0042] (3) Bisphenol F phenolic resin

[0043] Bisphenol F phenolic resin, solid, softening point 100-110℃, prepared according to the conventional preparation method of thermoplastic phenolic resin, wherein the weight ratio of bisphenol F to phenol is 1:2, the molar ratio of phenol to formaldehyde is 1:(0.78-0.82), free phenol ≤4.5, and the polymerization rate is 90-120S. The determination of technical indicators of phenolic resin is carried out according to GB / T 30772-2014.

[0044] As can be seen from Table 1, the raw materials of Examples 1-5 are all in accordance with the ratio specified in the present invention, using dimethyl ether type thermosetting phenolic resin, hydroxymethyl type thermosetting phenolic resin and bisphenol F phenolic resin as adhesives, cellulose and glass fiber as reinforcing fibers, and flame retardants, curing accelerators, and release agents, so that the products after material molding are free of ammonia and halogen, have high flame retardancy, flammability (UL94) (1.6mm), reach V-0 grade, high temperature resistance (heat deformation temperature greater than 190°C), good mechanical strength (bending strength greater than 110MPa), and excellent electrical properties (PTI reaches 200). Comparative Example 1 also uses most of the materials of Examples 1-5, but replaces bisphenol F phenolic resin with ordinary thermoplastic phenolic resin, and the anti-tracking index PTI is only 175. It can be seen that the present invention uses the compounding of two solid thermosetting phenolic resins and bisphenol F phenolic resin, which has a synergistic effect on the high temperature resistance, mechanical properties and electrical properties of the phenolic molding material finally obtained.

[0045] Therefore, the ammonia-free and halogen-free highly flame-retardant phenolic molding compound provided by the present invention can be applicable to the requirements of high-end electronic and electrical appliance accessory materials.

[0046] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An ammonia-free and halogen-free highly flame-retardant phenolic molding compound, characterized in that: The raw materials include the following weight percentages:

2. The ammonia-free and halogen-free highly flame-retardant phenolic molding compound according to claim 1, characterized in that: The preparation method of the dimethyl ether type thermosetting phenolic resin comprises the following steps: adding phenol and formaldehyde in a certain molar ratio into a reaction kettle equipped with a reflux condenser, a stirrer, a heating device and a dehydration device; then adding 0.5%-2% of the total feed amount of zinc acetate into the reaction mixture, and adjusting the pH value to 4.5-5.0; then heating to 80-90°C, reflux reaction for 2-3 hours, and then reducing pressure and dehydrating; finally raising the temperature to 130°C to remove phenol until the desired softening point is reached to obtain the dimethyl ether type thermosetting phenolic resin (solid); the molar ratio of phenol to formaldehyde is 1:(1.4-1.5), the softening point is 70-75°C, the free phenol is ≤5.5, and the polymerization rate is 120-180S.

3. The ammonia-free and halogen-free highly flame-retardant phenolic molding compound according to claim 1, characterized in that: The preparation method of the hydroxymethyl type thermosetting phenolic resin comprises the following steps: phenol and formaldehyde (F) are charged into a reaction kettle equipped with a reflux condenser, a stirrer, a heating device and a dehydration device according to a certain ratio; then, liquid alkali with a mass percentage concentration of 50% is added to the reaction mixture, the pH value in the reaction system is adjusted to 9.0, the reaction temperature is controlled at 65-68°C, and the reaction is carried out for 1 hour; then, the temperature is raised to 78-80°C for reflux reaction for 1.5 hours; cooling to 50°C, adding phosphoric acid, adjusting the pH value to 7.0-7.1, then gradually increasing the vacuum degree to above -0.095Mpa, dehydration is carried out, and finally the temperature is raised to 98°C to remove phenol until the desired softening point is reached, and finally the hydroxymethyl type thermosetting phenolic resin is obtained; the molar ratio of phenol to formaldehyde is 1:(1.8-1.9), the softening point is 65-70°C, the free phenol is ≤5.5, and the polymerization rate is 50-90S.

4. The ammonia-free and halogen-free highly flame-retardant phenolic molding compound according to claim 1, characterized in that: The bisphenol F phenolic resin is a bisphenol F modified phenolic resin, the weight ratio of bisphenol F to phenol is 1:2, the molar ratio of phenol to formaldehyde is 1:(0.78-0.82), free phenol is ≤4.5, the softening point is 100-110°C, and the polymerization speed is 90-120S.

5. The ammonia-free and halogen-free highly flame-retardant phenolic molding compound according to claim 1, characterized in that: The cellulose is purified wood fiber or cotton fiber, with a cellulose content of ≥98% and a fineness of 60-200 meshes.

6. The ammonia-free and halogen-free highly flame-retardant phenolic molding compound according to claim 1, characterized in that: The glass fiber is an alkali-free glass fiber with a diameter of 11-13 μm and a length of 1-5 mm.

7. The ammonia-free and halogen-free highly flame-retardant phenolic molding compound according to claim 1, characterized in that: The flame retardant is selected from zinc borate and aluminum hydroxide or a mixture of the two.

8. The ammonia-free and halogen-free highly flame-retardant phenolic molding compound according to claim 1, characterized in that: The curing accelerator is selected from one or more of magnesium oxide, calcium oxide and calcium hydroxide.

9. The ammonia-free and halogen-free highly flame-retardant phenolic molding compound according to claim 1, characterized in that: The release agent is selected from one or more of calcium stearate, zinc stearate, lithium stearate, stearic acid, stearic acid amide and ethylene bis stearic acid amide.

10. A method for preparing the ammonia-free and halogen-free highly flame-retardant phenolic molding compound according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: firstly, superfinely grinding dimethylene ether type thermosetting phenolic resin, hydroxymethyl type thermosetting phenolic resin, bisphenol F phenolic resin and curing accelerator to a fineness of more than 200 meshes, then uniformly mixing the mixture with other raw materials, heating and kneading or extruding, and finally granulating and forming, so as to obtain the ammonia-free and halogen-free highly flame-retardant phenolic molding material.

Images