Low-hardness solid silicone rubber composition and preparation method thereof

Abstract

The invention provides a low-hardness solid silicone rubber composition and a preparation method thereof. The low-hardness solid silicone rubber composition comprises the following raw materials in parts by weight: 93-100 parts of methyl vinyl silicone rubber raw rubber, 30-40 parts of white carbon black, 3.3-5.5 parts of a structured control agent, 4-6.5 parts of vinyl-terminated silicone oil, 1-2 parts of a diluent, 0.05-0.2 part of an internal release agent and 0.1-0.3 part of deionized water. The composition provided by the invention improves the processability of later open milling and extrusion molding, increases the smoothness before and after vulcanization, is not easy to separate out and remain, is not easy to migrate after being prepared into a finished product rubber compound, and accords with related food-grade certification. According to the preparation method, the surface glossiness of the rubber material is further improved, and the extrusion molding smoothness of the silicone rubber is improved.

Description

Technical Field

[0001] The invention belongs to the field of silicone rubber, and in particular relates to a low-hardness solid silicone rubber composition and a preparation method thereof. Background Art

[0002] The high-temperature silicone rubber sold on the market is mainly divided into solid silicone rubber and liquid silicone rubber. The molding methods of solid silicone rubber include compression molding, extrusion molding, calendering molding, etc. Low-hardness solid mixed rubber will be subject to greater filter resistance and friction such as the inner wall of the head during circumferential and axial movement in the extruder. The low-hardness rubber has a small amount of white carbon black filling and a high proportion of raw rubber. A large amount of dimethyl silicone oil is required to reduce the hardness, and the rubber is in a soft and sticky state. Therefore, the rubber has a large friction with the inner wall of the head and the mold surface during the extrusion process, which can easily cause the surface of the rubber to be rough, and then the inner and outer surfaces of the product are not smooth. In addition, the low-hardness rubber has a small amount of white carbon black, and it is difficult to evenly disperse the raw rubber and white carbon black during the mixing stage. During extrusion molding, it is easy for undispersed white carbon black particles to appear inside and outside the product, which can also easily cause the surface of the extruded product to be uneven.

[0003] The low-hardness solid silicone rubber on the market has a Shore hardness of 20-40HA, which is widely used in extruded tubes, extruded sealing strips, wires and cables and other products. Customers generally require low hardness, smooth inside and outside of the extruded products after molding, and no particles. As the application area gradually expands, people have higher and higher requirements for silicone rubber. In the fields of baby straws, skin-friendly cables, etc., there are other personalized requirements, such as mechanical strength (tensile strength ≥8.0Mpa, tear strength ≥20N / mm), food grade migration requirements (GB 4806), etc.

[0004] In the existing technical scheme, the traditional hardness control method is to control the crosslinking density, filler amount and diluent. The conventional method to control the crosslinking density is to reduce the average vinyl content, and reduce the crosslinking density while ensuring a certain degree of crosslinking, thereby obtaining a lower hardness. However, due to the sudden drop in crosslinking density, the physical properties after vulcanization are low, and it is very easy to have undesirable conditions such as breakage at the subsequent application end, and the strength of the material cannot be guaranteed; the hardness of silicone rubber can be reduced by reducing the amount of filler in the rubber, but the strength of the material cannot be guaranteed; adding diluents (such as dimethyl silicone oil) to solid silicone rubber can reduce the hardness of silicone rubber, thereby obtaining low-hardness silicone rubber, but the diluents commonly added at present do not participate in the reaction and are easy to precipitate, making the rubber sticky, and cannot meet the food grade migration requirements (GB 4806). Patent CN103613935A discloses a low-hardness extruded rubber and a preparation method thereof, wherein the raw material composition of the low-hardness extruded rubber is 100 parts by mass of raw rubber with a vinyl molar content of 0.03% and 20-30 parts by mass of hydrophobic fumed silica. The product has good extrusion processing characteristics after actual testing and can meet the use requirements of making extruded tubes. The preparation method is easy to operate. However, the tensile strength (4Mpa) and tear strength (15N / mm) obtained in the end are too low to meet the performance requirements of the subsequent extruded finished products. Patent CN102888119A discloses a low-hardness mixed silicone rubber composition and a preparation process, which includes 80-120 parts of methyl vinyl silicone rubber raw rubber, 0.5-5 parts of silicone oil, 2-8 parts of dihydroxy polydimethylsiloxane, 30-60 parts of white carbon black, and 0.1-3 parts of dimethyl di-tert-butyl peroxyhexane. The invention is prepared by reducing the filling amount of white carbon black and adding a large amount of low-viscosity silicone oil that does not participate in the reaction. Reducing the amount of white carbon black is not conducive to the smoothness of the later extrusion molding. Adding a large amount of low-viscosity silicone oil will also affect the smoothness of the extruded product. At the same time, it is easy to precipitate in the later stage, affecting food grade certification.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a new low-hardness solid silicone rubber composition, which improves the processability of later mixing and extrusion molding, increases the smoothness before and after vulcanization, is not easy to precipitate and remain, is not easy to migrate after being made into a finished mixed rubber, and meets the relevant later food grade certification.

[0007] The basic concept of the technical solution of the present invention is as follows:

[0008] A low-hardness solid silicone rubber composition, the raw material formula of which is as follows:

[0009]

[0010]

[0011] As one embodiment, the methyl vinyl silicone rubber raw rubber is: methyl terminated methyl vinyl silicone rubber raw rubber and vinyl terminated methyl vinyl silicone rubber raw rubber.

[0012] Preferably, the weight ratio of the methyl-terminated methyl vinyl silicone rubber raw rubber to the vinyl-terminated methyl vinyl silicone rubber raw rubber is 1 to 2.95.

[0013] As a method, the characteristic parameters of the methyl vinyl silicone rubber raw rubber are: 500000-750000 g / mol, and the molar percentage of vinyl is 0.03% to 0.16%.

[0014] As a method, the white carbon black has a specific surface area of ​​200 to 380 m 2 / g of fumed silica.

[0015] As a method, the characteristic parameters of the vinyl-terminated silicone oil are: the vinyl molar percentage is 0.05 to 0.2, and the viscosity at 25°C is (5 to 12)×10 4 mm 2 / s.

[0016] As one embodiment, the structure control agent is one or more combinations of hydroxy silicone oil, dimethyldimethoxysilane and hexamethyldisilazane.

[0017] As one embodiment, the diluent is dimethicone.

[0018] The present invention provides a method for preparing the low-hardness solid silicone rubber composition as described in any one of the above, comprising the following steps:

[0019] Step 1: putting an internal mold release agent and part of the methyl vinyl silicone rubber raw rubber into a kneader, and then adding a part of the formula amount of the structuring control agent, the vinyl-terminated silicone oil, deionized water and a diluent to obtain a first mixed material;

[0020] Step 2: Put the white carbon black into a kneader in batches, then add the remaining methyl vinyl silicone rubber raw rubber, mix, and finally add the remaining formula amount of the structuring control agent, the vinyl-terminated silicone oil, deionized water and the diluent, control the mixing and place it to obtain a second mixed material;

[0021] Step 3: heating, vacuuming, kneading, and obtaining a mixed base rubber;

[0022] Step 4: Discharging the material at a temperature of ≤120° C. to obtain the low-hardness solid silicone rubber composition.

[0023] As one approach, in step 2, the temperature of the mixture is controlled to be ≤70°C and the standing time is 4 to 8 hours.

[0024] As one method, in step 3, the kneading machine is heated to 140-180° C., evacuated to -0.065-0.75 MPa, and kneaded for 2-6 hours.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. The formula of the present invention adopts a composite system of white carbon black, silane-type structural control agent, high viscosity terminal vinyl silicone oil and methyl-terminated methyl vinyl silicone rubber raw rubber. The appropriate amount of white carbon black improves the soft and sticky state of the silicone rubber composition, increases the smoothness of the rubber surface, and improves the processability of later refining and extrusion molding, thereby reducing the resistance of the rubber extrusion molding process and increasing the smoothness before and after vulcanization. The silane-type structural control agent participates in the chemical reaction, has a good treatment effect, is not easy to precipitate or remain, and is not easy to migrate after being made into a finished mixed rubber, which meets the relevant food grade certification in the later period. The high viscosity terminal vinyl silicone oil increases the smoothness of silicone rubber extrusion while enhancing the tensile strength. At the same time, it also increases the problem of poor fluidity caused by the increase in the amount of white carbon black filling, and increases the fluidity of silicone rubber. In addition, the terminal vinyl silicone oil participates in cross-linking and will not precipitate, which meets the food grade certification. The methyl-terminated methyl vinyl silicone rubber raw rubber has lower hardness, avoiding the reduction of hardness due to the introduction of a large amount of dimethyl silicone oil, causing the silicone oil in the rubber to precipitate and cause stickiness (stickiness will make the rubber too resistant during the extrusion molding process, causing extrusion difficulties and resulting in an uneven extruded surface).

[0027] 2. The present invention further optimizes the preparation process, and adds methyl vinyl silicone rubber raw rubber in proportion at different stages, thereby increasing the dispersion of white carbon black and methyl vinyl silicone rubber raw rubber, allowing white carbon black to fully blend with the methyl vinyl silicone rubber raw rubber, increasing the surface gloss of the rubber, and improving the smoothness of silicone rubber extrusion molding; in addition, the liquid additive is added in multiple times to avoid excessive liquid additives during the early mixing, which causes the rubber to slip, deteriorates the dispersion effect of white carbon black and other components such as raw rubber, and causes the surface of the extruded product after the rubber is vulcanized to be rough. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] The "parts" in the following embodiments are "parts by mass". The measurement units of "parts" or "parts by mass" in the same embodiment are unified, which is the same as the idea of ​​the technical solution defined by specific units of measurement and does not affect its feasibility.

[0030] Unless otherwise specified, "%" means molar percentage "mol %" in relation to the vinyl content.

[0031] The specific embodiment of the present invention prepares low hardness (20-40HA) extrusion-molded solid silicone rubber, and the specific information of the raw materials used is shown in Table 1.

[0032] Table 1

[0033]

[0034]

[0035] The above-mentioned methyl vinyl silicone rubber raw rubber includes: methyl terminated methyl vinyl silicone rubber raw rubber and vinyl terminated methyl vinyl silicone rubber raw rubber.

[0036] As an example, the method for preparing the low-hardness solid silicone rubber composition adopted in the embodiment comprises the following steps:

[0037] Step 1: placing an internal mold release agent and the first batch of methyl vinyl silicone rubber raw rubber into a kneader, adding a portion of the formula amount of a structuring control agent, deionized water, vinyl-terminated silicone oil, a diluent and other liquid additives to obtain a first mixed material;

[0038] Step 2: Put the white carbon black into the kneader in batches, then add the remaining methyl vinyl silicone rubber raw rubber, mix, and finally add the remaining formula amount of the structure control agent, deionized water, terminal vinyl silicone oil and diluent and other liquid additives, and control the mixing temperature not to exceed 70°C, and place it for 4 to 8 hours to obtain the second mixed material;

[0039] Step 3: Heat the kneader to 140-180° C., evacuate to -0.065-0.75 MPa, and knead for 2-6 hours to obtain a mixed base rubber;

[0040] Step 4: When the temperature is ≤120℃, discharge the material.

[0041] The mixed rubber material can be formed by adding a vulcanizing agent, and the vulcanizing agent can be selected from 2,5-dimethyl-2,5-di-tert-butyl peroxide hexane, diisopropylbenzene peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide or platinum vulcanizing agent.

[0042] Example 1

[0043]

[0044] In this embodiment 1, the preparation method of the low hardness solid silicone rubber composition is as follows:

[0045] Step 1: Put an internal mold release agent and 70.8 parts of methyl vinyl silicone rubber into a kneader, and then add 70% of the formula amount of a structure control agent, terminal vinyl silicone oil, deionized water, a diluent and other liquid additives to obtain a first mixed material;

[0046] Step 2: 31.3 parts of white carbon black are added into a kneader in three portions, and then the remaining 25 parts of methyl vinyl silicone rubber are added and mixed, and finally the remaining 30% of the formula amount of the structure control agent, the end vinyl silicone oil, the deionized water and the diluent and other liquid additives are added, and the mixing temperature is controlled not to exceed 70°C, and the mixture is placed for 4-8 hours to obtain a second mixed material;

[0047] Step 3: Heat the kneader to 160°C, evacuate to -0.065-0.75Mpa, and knead for 3 hours to obtain a mixed base rubber;

[0048] Step 4: When the temperature is ≤120℃, discharge the material.

[0049] In the above steps, the methyl vinyl silicone rubber raw rubber includes methyl-terminated methyl vinyl silicone rubber raw rubber and vinyl-terminated methyl vinyl silicone rubber raw rubber. The specific types, parameters and amounts of the raw materials added in batches are shown in Table 2.

[0050] Embodiment 2-4

[0051] In Examples 2-4, the dosage of components and some processes are adjusted on the basis of Example 1, as shown in Table 2. The performance parameters of the same raw materials are consistent with those in Example 1.

[0052] The specific parameters of Examples 1-4 and the product properties after vulcanization molding are shown in Table 2.

[0053] Table 2

[0054]

[0055]

[0056] Note: 1. "30% secondary" in the diluent means that 30% of the diluent is added in the second feeding.

[0057] Examples 1-4 show that based on the technical solution of the present invention, low-hardness extruded solid silicone rubber is obtained, and the surface of the extruded product is smooth and free of particles, and has a certain strength, which can meet the application requirements of bionics-related fields.

[0058] Comparative Examples 1-7

[0059] In order to compare and examine the advantages of the technical solution of the present invention, the present invention also implemented comparative examples 1 to 7. The specific parameters of comparative examples 1 to 7 and the product performance after vulcanization molding are shown in Table 3.

[0060] Table 3

[0061]

[0062]

[0063] Compared with Example 1, Comparative Example 1 does not use the process of adding methyl vinyl silicone rubber and liquid additives twice in the mixing process. The surface of the low-hardness solid silicone rubber product prepared after extrusion molding is rough and has obvious particles.

[0064] Compared with Example 2, Comparative Example 2 chose to add a large amount of dimethyl silicone oil to dilute the rubber to reduce the hardness. The surface of the prepared low-hardness solid silicone rubber was sticky, the rubber was sticky during extrusion molding, and the surface of the product after extrusion molding was dark and matte, which could not meet food grade certification.

[0065] Compared with Example 3, Comparative Example 3 does not use the addition of high-viscosity terminal vinyl silicone oil, which affects the appearance of the rubber compound and the smoothness of the extruded product and cannot meet the appearance requirements. At the same time, the physical tensile strength and tear strength properties are also significantly reduced.

[0066] Compared with Example 4, Comparative Example 4 reduces the mass fraction of white carbon black to reduce the hardness. The white carbon black fraction drops sharply, causing a significant decrease in physical properties. At the same time, the smoothness of the product after extrusion molding deviates, and there are obvious particles, which cannot meet the appearance requirements.

[0067] Compared with Example 2, in Comparative Example 5, only hydroxy silicone oil was selected as the structuring control agent. Hydroxy silicone oil treated white carbon black through physical interaction force. After a large amount was added, the plasticity of the rubber compound became very low, the rubber compound was soft and sticky, and the surface of the extruded tube was not smooth, which could not meet the food grade certification.

[0068] Compared with Example 2, Comparative Example 6 uses fully methyl-terminated methyl vinyl silicone rubber raw rubber, and the produced rubber has low hardness, low tear and tensile strength, and cannot meet the basic physical property requirements.

[0069] Compared with Example 3, Comparative Example 7 uses fully vinyl-terminated methyl vinyl silicone rubber raw rubber, and the hardness of the produced rubber is higher, exceeding the hardness range.

Claims

1. A low-hardness solid silicone rubber composition, the raw material formula of which is as follows:

2. The low-hardness solid silicone rubber composition according to claim 1, characterized in that: The methyl vinyl silicone rubber raw rubber is: methyl terminated methyl vinyl silicone rubber raw rubber and vinyl terminated methyl vinyl silicone rubber raw rubber; Preferably, the weight ratio of the methyl-terminated methyl vinyl silicone rubber raw rubber to the vinyl-terminated methyl vinyl silicone rubber raw rubber is 1 to 2.

95.

3. The low-hardness solid silicone rubber composition according to claim 2, characterized in that: The characteristic parameters of the methyl vinyl silicone rubber are: 500000-750000 g / mol, and the molar percentage of vinyl is 0.03%-0.16%.

4. The low-hardness solid silicone rubber composition according to claim 1, characterized in that: The white carbon black has a specific surface area of ​​200 to 380 m 2 / g of fumed silica.

5. The low-hardness solid silicone rubber composition according to claim 1, characterized in that: The characteristic parameters of the vinyl-terminated silicone oil are: the molar percentage of vinyl is 0.05-0.2, the viscosity at 25°C is (5-12)×10 4 mm 2 / s.

6. The low-hardness solid silicone rubber composition according to claim 1, characterized in that: The structural control agent is one or a combination of hydroxy silicone oil, dimethyldimethoxysilane and hexamethyldisilazane.

7. The low-hardness solid silicone rubber composition according to claim 1, characterized in that: The diluent is dimethyl silicone oil.

8. A method for preparing a low-hardness solid silicone rubber composition according to any one of claims 1 to 7, comprising the following steps: Step 1: putting an internal mold release agent and part of the methyl vinyl silicone rubber raw rubber into a kneader, and then adding a part of the formula amount of the structuring control agent, the vinyl-terminated silicone oil, deionized water and a diluent to obtain a first mixed material; Step 2: Put the white carbon black into a kneader in batches, then add the remaining methyl vinyl silicone rubber raw rubber, mix, and finally add the remaining formula amount of the structuring control agent, the vinyl-terminated silicone oil, deionized water and the diluent, control the mixing and place it to obtain a second mixed material; Step 3: heating, vacuuming, kneading, and obtaining a mixed base rubber; Step 4: Discharging the material at a temperature of ≤120° C. to obtain the low-hardness solid silicone rubber composition.

9. The method for preparing a low-hardness solid silicone rubber composition according to claim 8, characterized in that: In step 2, the temperature of the mixture is controlled to be ≤70° C. and the storage time is 4 to 8 hours.

10. The method for preparing a low-hardness solid silicone rubber composition according to claim 8, characterized in that: In step 3, the kneading machine is heated to 140-180° C., evacuated to -0.065-0.75 MPa, and kneaded for 2-6 hours.

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