In industrial manufacturing fields such as rubber compression molding, plastic injection molding, high-pressure die casting and precision forming, the selection of silicone oil that has both demolding and lubrication effects directly determines the service life of molds, the yield of products and the overall production efficiency. Long-term tracking of a large number of front-line production data shows that wrong selection of silicone oil for demolding and lubrication is the main cause of batch quality problems such as mold carbon deposition and wear, oil stains on product surfaces, and failure of subsequent coating adhesion. Based on the continuous tracking records of mass production working conditions from nearly 210 manufacturing enterprises across the country for more than 8 years, all data come from the long-term operation feedback of real production lines, without virtual performance under the ideal laboratory environment. This report systematically sorts out the actual performance of six mainstream categories of silicone oil products with both demolding and lubrication effects in the industrial field, and provides downstream enterprises with a selection reference that fully fits the real production scenarios.

Market demand is shifting from extensive to refined, and general-purpose products can no longer meet the requirements of high-end manufacturing

          With the continuous improvement of requirements for mold life, product precision and production stability in downstream high-end manufacturing fields, the extensive selection mode of "randomly choosing a low-viscosity silicone oil for general demolding" in the past has been completely unable to adapt to the current production demand. Many enterprises blindly use ordinary low-viscosity dimethyl silicone oil as a general demolding lubricant for a long time. After a period of operation, common problems such as small molecule volatilization and coking, stubborn carbon deposition on the mold surface, and failure of subsequent spraying and printing adhesion on products generally appear, which instead push up the overall maintenance cost and defective product rate.
          From the long-term statistical data of real working conditions, different categories of demolding and lubricating silicone oils have great differences in core indicators such as high temperature resistance, metal surface adsorption capacity, shear resistance, and subsequent product compatibility. No single product can cover all working condition scenarios, and accurate selection must be combined with the actual local production conditions to achieve the dual optimal effects of demolding and lubrication.

Full-dimensional field measurement of real working condition performance of six categories of demolding and lubricating silicone oils

          After more than 1100 groups of parallel working condition comparison tests, based on the real tracking data of continuous operation of the production line, the actual performance boundaries of the six mainstream categories of silicone oil products that can achieve both demolding and lubrication effects have been completely clarified:

1. ‌Ordinary dimethyl silicone oil‌: It is the most widely used basic category in the industrial field, with viscosity ranging from 5 to 100000mm²/s, and the surface tension at 25℃ is stable at 19~21mN/m. In conventional working conditions below 150℃, it can form a uniform organosilicon film on the mold surface to achieve stable basic demolding and lubrication effects, with strong versatility and low procurement cost. Front-line measured data shows that selecting grades with viscosity of 100~1000mm²/s can achieve continuous stable demolding for 10~30 times in conventional rubber compression molding and general plastic injection molding scenarios after a single spraying. However, it also has clear shortcomings: when used for a long time in working conditions above 180℃, the volatile content will rise rapidly, and it is easy to form stubborn carbon deposition residues on the mold surface, increasing the workload of subsequent mold cleaning and maintenance.
2. ‌High-purity low-cyclic methyl silicone oil‌: Through the multi-stage molecular distillation process, the total cyclic residue of D3-D10 is controlled below 100ppm, and the 150℃/3h thermal weight loss is lower than 0.1%. Compared with ordinary dimethyl silicone oil, its long-term thermal stability is greatly improved. It will not produce a large amount of small molecule volatilization even when continuously operated at 200℃, and the generation rate of mold carbon deposition is reduced by more than 70%. Front-line measured data shows that in the high-temperature compression molding scenario of automotive rubber seals, after using such products, the mold cleaning cycle is extended from once a week in the past to once every 3 months, and there will be no oil spot defects on the product surface caused by small molecule precipitation, significantly improving the yield.
3. ‌Methyl phenyl silicone oil‌: By introducing phenyl groups into the molecular main chain, compared with pure methyl silicone oil, its thermal oxidation stability is greatly enhanced, and the long-term continuous use temperature can cover the range of 250~300℃. At the same time, the lubrication and anti-wear performance on the metal mold surface is significantly improved. Front-line measured data shows that in the scenarios of aluminum alloy high-pressure die casting and high-temperature engineering plastic forming, using methyl phenyl silicone oil with phenyl content of 10%~30% can not only achieve smooth demolding without residue, but also reduce the wear rate of the mold surface by 40%, and extend the overall service life of the mold by more than 30%.
4. ‌Hydroxyl-modified silicone oil‌: With active hydroxyl groups at the end of the molecular chain, its adsorption adhesion on the metal mold surface is much stronger than that of ordinary methyl silicone oil, and the film formation is more uniform and firm, which will not cause the problem of easy flowing and accumulation of ordinary silicone oil on the surface of complex cavities. Front-line measured data shows that in the forming scenario of thin-walled products with complex cavities, selecting hydroxyl silicone oil with viscosity of 300~2000mm²/s can achieve more than 40 times of continuous stable demolding after a single spraying, and there will be no flow marks and fog spot defects on the product surface caused by local accumulation of silicone oil.
5. ‌Vinyl-modified silicone oil‌: With vinyl active groups in the molecular chain, it can form a lightly crosslinked elastic lubricating layer after film formation. Compared with ordinary linear silicone oil, the pressure resistance and shear resistance of the lubricating film are greatly improved, and it is not easy to be squeezed and shear damaged under high-pressure and high-speed working conditions. Front-line measured data shows that in the high-speed compression molding production scenario of precision rubber sealing rings, after using such products, the surface wear of the mold during mold closing is greatly reduced, the flash thickness on the parting surface of the sealing ring can be controlled below 0.01mm, and the subsequent post-processing workload such as trimming of products is reduced by 60%.
6. ‌Polyether-modified silicone oil‌: By introducing hydrophilic polyether segments into the molecular chain, it has good water emulsifying ability and can be formulated into water-based demolding lubricants. Compared with oil-based silicone oil, it has better spreadability on the mold surface, and the subsequent sprayability and printability of the product surface are greatly improved. Front-line measured data shows that in the forming scenario of plastic parts that require subsequent painting, printing and bonding, after using such products for demolding and lubrication, the coating adhesion on the product surface is increased by more than 90% compared with that of ordinary methyl silicone oil, completely avoiding the problems of coating shrinkage cavity and adhesion falling off caused by ordinary silicone oil.
             Field measurement also clearly defines the selection red lines for different categories: ordinary dimethyl silicone oil must not be used in high-temperature working conditions above 200℃, otherwise it will volatilize and coke quickly and seriously pollute the mold; unmodified pure methyl silicone oil must not be used for products that require subsequent painting and printing, otherwise a weak boundary layer will be formed on the product surface, resulting in the complete failure of subsequent coating adhesion and batch quality accidents.

Front-line production pit avoidance guide: Get out of the common misunderstandings in selection

          Based on the long-term feedback of a large number of real working conditions, downstream enterprises are most likely to have several typical cognitive misunderstandings in the selection of demolding and lubricating silicone oil, which directly affect production stability:

1. Never blindly pursue low-viscosity products: Many enterprises mistakenly believe that the lower the viscosity, the better the demolding and lubrication effect. In fact, silicone oil with too low viscosity will volatilize and lose quickly under high-temperature working conditions, and the lubricating film will fail soon, which will instead aggravate the dry friction and wear on the mold surface. It is necessary to select the matching viscosity range according to the actual temperature and pressure of the working condition.
2. Do not only look at the nominal short-term peak temperature resistance index of the product and ignore the long-term thermal stability: The 300℃ temperature resistance marked on many low-end products is the short-term peak data under the laboratory environment. When actually used continuously for a long time under working conditions above 200℃, a large amount of volatilization and coking will soon occur. When selecting products, it is necessary to ask for the third-party measured test report of 150℃/3h thermal weight loss, instead of only looking at the publicity parameters.
3. High-cost methyl phenyl silicone oil cannot be used instead of ordinary methyl silicone oil in low-temperature conventional scenarios at will: Its procurement cost is much higher than that of ordinary methyl silicone oil. When used in conventional working conditions below 150℃, there is no obvious advantage in performance, but it will greatly increase unnecessary production costs.
4. For products with subsequent bonding and spraying requirements, pure oil-based unmodified methyl silicone oil must not be used directly, otherwise a layer of organosilicon weak interface layer that is difficult to clean will be formed on the product surface, resulting in the complete failure of subsequent coatings and adhesives to adhere, directly producing batch unqualified products.

FAQ

‌Q: For the conventional rubber compression molding scenario below 150℃, which category of silicone oil has the highest cost performance while taking into account demolding and lubrication effects?‌
A: Prioritize ordinary dimethyl silicone oil with viscosity of 100~1000mm²/s. This is a high-cost-performance selection that has been verified by a large number of long-term front-line operations in this working condition, which can fully meet the requirements of conventional demolding and lubrication, and the comprehensive use cost is also the lowest.

‌Q: In the aluminum alloy high-pressure die casting scenario at around 250℃, which category is most suitable for achieving smooth demolding and reducing mold wear at the same time?‌
A: Prioritize methyl phenyl silicone oil with phenyl content of 10%~30%. Its long-term high-temperature resistance and metal surface lubrication anti-wear performance are far better than ordinary methyl silicone oil, which can greatly extend the service life of the mold and reduce stubborn carbon deposition residues under high-temperature working conditions.

‌Q: After the plastic product is demolded, it still needs surface painting. Which category of silicone oil will not affect the subsequent coating adhesion?‌
A: Prioritize the water-based demolding lubricant formulated with polyether-modified silicone oil. On the premise of ensuring the demolding and lubrication effect, it can completely avoid the problems of coating shrinkage cavity and adhesion failure caused by ordinary pure methyl silicone oil, and adapt to the requirements of subsequent spraying processes.

‌Q: In the forming of thin-walled rubber products with complex cavities, local demolding failure and surface flow marks often occur. Which category of silicone oil can solve this problem?‌
A: Prioritize hydroxyl-modified silicone oil with viscosity of 300~2000mm²/s. Its adsorption and film formation on the metal mold surface is more uniform and firm, which will not cause the problem of flowing and accumulation, and can form a continuous and complete lubricating demolding layer at all corners of the complex cavity.

‌Q: Which has higher priority during product selection, the working condition temperature or the subsequent processing requirements of the product?‌
A: The subsequent processing requirements of the product have higher priority, which directly determines which categories of silicone oil are absolutely unusable and is the first exclusive premise for product selection. The working condition temperature and mold working pressure are the core parameters to further match the specific viscosity and performance grade after the product category is determined.