Release film for foamed silica gel and preparation method thereof

Abstract

The invention discloses a release film for foamed silica gel and a preparation method of the release film, and belongs to the technical field of release film preparation. The release film for the foamed silica gel comprises a base material layer and a release coating, the release coating comprises the following raw materials: polydimethylsiloxane resin, polytetrafluoroethylene resin, an organic solvent, a fluorine-containing solvent, a cross-linking agent, an anchoring agent, a catalyst, a stripping agent, an inhibitor and an anti-sticking agent; the cross-linking agent is prepared from the following raw materials: polymethylhydrosiloxane and polytetrafluoroethylene resin. The invention further discloses a preparation method of the release film for the foamed silica gel. The invention can solve the problems of difficult stripping and quality damage of the foamed silica gel caused by adhesion due to interpenetration of the silicon release film and the foamed silica gel, and has the advantages of simple formula and easiness in preparation and operation.

Description

Technical Field

[0001] This invention belongs to the field of release film preparation technology, specifically relating to a release film for foamed silicone and its preparation method. Background Technology

[0002] Foamed silicone, as a new type of lightweight material, is widely used in construction, furniture, and automotive industries due to its sound insulation, heat insulation, good resilience, and high mechanical strength. Also known as addition-cure silicone, foamed silicone is a two-component thermosetting silicone rubber system. The two components are typically mixed in a 1:1 ratio. After foaming, its volume increases significantly, and after high-temperature curing, it forms a soft, elastic shock-absorbing material that combines functionality and practicality.

[0003] In the production of foamed silicone, the use of release film is essential. After being thoroughly stirred in a foaming machine, liquid silicone is evenly extruded through a specialized nozzle onto the surface of the release film on the calendering line. Then, another layer of release film is applied to form a sandwich structure. After being heated in an oven tunnel, the material completes the foaming, molding, and winding processes, ultimately forming the finished foamed silicone. In this process, the release film primarily performs three core functions: firstly, it acts as a support for the foam, ensuring uniform molding of the silicone; secondly, it uses surface coating technology to prevent adhesion between the silicone and the support film, avoiding delamination; and thirdly, it ensures the integrity of the silicone foam structure and maintains the stability of the material's performance.

[0004] However, existing release films still have some problems in use. For example, although fluoroplastic release films have excellent performance, their high cost limits their large-scale application; ordinary silicone release films are prone to chemical reactions with silicone during foaming, leading to permeation and affecting material uniformity. More importantly, localized point reactions occurring in some processes can cause damage when the silicone foam is torn, affecting both the appearance quality of the finished product and potentially reducing the material's lifespan.

[0005] In conclusion, as a core auxiliary material in the production of foamed silicone, the performance optimization and cost control of release film are crucial for improving product quality and driving industry development. Overcoming existing technological bottlenecks and achieving a more efficient and stable foamed silicone production system is one of the key technical challenges that urgently needs to be addressed in this field. Summary of the Invention

[0006] The problem this invention aims to solve is to provide a release film for foamed silicone and its preparation method, in order to address the issue that existing silicone-based release films and foamed silicone permeate each other, causing adhesion and making it difficult to peel off the foamed silicone, resulting in quality degradation.

[0007] The technical solution adopted to solve its technical problem is to provide a release film for foamed silicone, including a substrate layer and a release coating layer; The release coating comprises the following raw materials in parts by weight: 800-900 parts of polydimethylsiloxane resin, 100-200 parts of polytetrafluoroethylene resin, 1000-6000 parts of organic solvent, 50-200 parts of fluorinated solvent, 5-35 parts of crosslinking agent, 2-15 parts of anchoring agent, 10-30 parts of catalyst, 2-20 parts of release agent, 0.1-1.5 parts of inhibitor, and 1-10 parts of anti-sticking agent; The crosslinking agent comprises the following raw materials in parts by weight: 2-20 parts of polymethylhydrosiloxane and 3-15 parts of polytetrafluoroethylene resin.

[0008] Preferably, the release coating comprises the following raw materials in parts by weight: 800 parts of polydimethylsiloxane resin, 200 parts of polytetrafluoroethylene resin, 2000-4000 parts of organic solvent, 100-150 parts of fluorinated solvent, 10-30 parts of crosslinking agent, 2-10 parts of anchoring agent, 15-25 parts of catalyst, 5-15 parts of release agent, 0.5-1 part of inhibitor and 2-8 parts of anti-sticking agent; The crosslinking agent comprises the following raw materials in parts by weight: 5-20 parts of polymethylhydrosiloxane and 5-10 parts of polytetrafluoroethylene resin.

[0009] More preferably, the release coating comprises the following raw materials in parts by weight: 800 parts of polydimethylsiloxane resin, 200 parts of polytetrafluoroethylene resin, 2000 parts of organic solvent, 100 parts of fluorinated solvent, 30 parts of crosslinking agent, 5 parts of anchoring agent, 20 parts of catalyst, 10 parts of release agent, 1 part of inhibitor and 6 parts of anti-sticking agent. The crosslinking agent comprises the following raw materials in parts by weight: 20 parts of polymethylhydrosiloxane and 10 parts of polytetrafluoroethylene resin.

[0010] More preferably, the substrate layer is made of polyethylene terephthalate; the organic solvent is at least one of toluene, methyl ethyl ketone, No. 120 gasoline and ethyl acetate; the fluorinated solvent is tetrafluoroethyl solvent; the anchoring agent is a functionalized organosiloxane compound containing vinyl and epoxy groups; the catalyst is a platinum catalyst; the stripping agent is Dow 7201 and / or cyclohexanol R77; the inhibitor is ethynylcyclohexanol; and the anti-sticking agent is silica microspheres.

[0011] More preferably, the tetrafluoroethyl solvent is 1,1,2,2-tetrafluoroethyl ether.

[0012] This invention also provides a method for preparing the above-mentioned release film for foamed silicone, comprising the following steps: (1) Dissolve polydimethylsiloxane resin in 1 / 2 of the total weight of organic solvent by stirring to obtain premix 1; (2) Dissolve polytetrafluoroethylene resin in a fluorinated solvent by stirring to obtain premix 2; (3) Stir and disperse the anti-sticking agent in the remaining 1 / 2 of the total weight of organic solvent to obtain premix 3; (4) After mixing and stirring premix 1 and premix 2, add premix 3 and mix and stir to obtain mixture 4; (5) Add inhibitor, crosslinking agent, anchoring agent, catalyst and release agent to mixture 4 in sequence, mix well to obtain release coating liquid; (6) Apply the release coating liquid to the substrate layer and bake to obtain the release film for foamed silicone.

[0013] Preferably, in step (1), the stirring speed for dissolving is 2500~3500 r / min and the time is 2~6 min; in step (2), the stirring speed for dissolving is 250~350 r / min and the time is 5~15 min; in step (3), the stirring speed for dispersing is 250~350 r / min and the time is 2~6 min.

[0014] More preferably, in step (1), the stirring speed for dissolving is 3000 r / min and the time is 5 min; in step (2), the stirring speed for dissolving is 300 r / min and the time is 10 min; in step (3), the stirring speed for dispersing is 300 r / min and the time is 5 min.

[0015] Preferably, step (4) includes the following steps: mixing premix 1 and premix 2 at a speed of 250~350 r / min for 2~6 min, then adding premix 3 and mixing at a speed of 250~350 r / min for 5~15 min to obtain mixture 4.

[0016] More preferably, step (4) includes the following steps: mixing premix 1 and premix 2 at a speed of 300 r / min for 5 min, then adding premix 3 and mixing at a speed of 300 r / min for 10 min to obtain mixture 4.

[0017] Preferably, step (5) includes the following steps: adding inhibitor, crosslinking agent, anchoring agent, catalyst and release agent to mixture 4 in sequence and stirring at a speed of 250~350r / min for 2~6min to obtain release coating liquid.

[0018] More preferably, step (5) includes the following steps: adding inhibitor, crosslinking agent, anchoring agent, catalyst and release agent to mixture 4 in sequence and stirring at 300 r / min for 5 min to obtain release coating liquid.

[0019] Preferably, the baking temperature in step (6) is 130~150℃ and the baking time is 40~60s.

[0020] The beneficial effects of the above technical solution adopted in this invention are as follows: the crosslinking agent is composed of polymethylhydrosiloxane and polytetrafluoroethylene resin. The silicon-hydrogen bonds in the crosslinking agent and the anchoring agent with vinyl end groups undergo an addition reaction under the action of a catalyst. After the reaction at 130~150℃, Si-CC-Si bonds are formed, and finally a release coating is formed and attached to the substrate layer.

[0021] The present invention has the following beneficial effects: (1) This invention uses a combination of polytetrafluoroethylene resin and polydimethylsiloxane resin as the silicone resin, and polymethylhydrosiloxane and polytetrafluoroethylene resin as crosslinking agents, which significantly improves the stability of the release film and effectively solves the problem that the silicone oil layer of traditional release films is prone to aging after long-term use or in high-temperature environments, which leads to unstable release force of the release film. At the same time, by adding functionalized organosiloxane compounds containing vinyl and epoxy groups as anchoring agents, the bonding force between the release coating and the substrate is enhanced, the adhesion performance of the release film is improved, and the shortcomings of insufficient adhesion in the prior art are overcome. Secondly, acetylene alcohol inhibitors containing acetylene groups are introduced into the release coating. By adjusting the degree of crosslinking of the silicone resin, the surface of the release film is softened and wear-resistant, which effectively promotes the uniform foaming of silicone. Furthermore, by adding silica microspheres to form an uneven interface in the release coating, the oily and sticky phenomenon caused by the high dry silicone content of the release film is improved, thereby enhancing the dryness of the release film surface and preventing the release film from adhering to the foamed silicone.

[0022] (2) In the preparation method of the present invention, the stepwise preparation of the premix avoids precipitation or agglomeration caused by direct contact between components. For example, the separate dissolution of polydimethylsiloxane resin and polytetrafluoroethylene resin can prevent early cross-linking. Combined with mechanical stirring, it ensures that the anti-sticking agent is uniformly dispersed in the organic solvent, and finally forms a homogeneous coating, which effectively reduces the damage caused by local spot reactions. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments.

[0024] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0025] The features and performance of the present invention will be further described in detail below with reference to the embodiments. The polydimethylsiloxane resin, polymethylhydrosiloxane, and ethynylcyclohexanol are all sourced from Cyrosac (Shanghai) New Materials Co., Ltd.; the polytetrafluoroethylene resin is sourced from Shanghai Zhongboli Chemical Technology Co., Ltd.; the functionalized organosiloxane compound containing vinyl and epoxy groups and the platinum catalyst are both sourced from Dow Corning Incorporated; and the silica microspheres are sourced from Changxing Chemical Industry Co., Ltd.

[0026] Example 1 A release film for foamed silicone includes a substrate layer made of polyethylene terephthalate and a release coating layer. The release coating comprises the following raw materials in parts by weight: 900 parts of polydimethylsiloxane resin, 100 parts of polytetrafluoroethylene resin, 2000 parts of organic solvent, 100 parts of 1,1,2,2-tetrafluoroethyl ethyl ether, 15 parts of crosslinking agent, 5 parts of functionalized organosiloxane compound containing vinyl and epoxy groups, 20 parts of platinum catalyst, 6 parts of seroxac R77, 1 part of ethynylcyclohexanol, and 4 parts of silica microspheres. The organic solvent is a mixture of toluene, methyl ethyl ketone, No. 120 gasoline and ethyl acetate in a mass ratio of 1:1:1:1; the crosslinking agent includes the following raw materials in parts by weight: 10 parts of polymethylhydrosiloxane and 5 parts of polytetrafluoroethylene resin.

[0027] This embodiment also provides a method for preparing the release film for the above-mentioned foamed silicone, including the following steps: (1) Mix polydimethylsiloxane resin and 1 / 2 of the total weight of organic solvent and stir at 3000 r / min for 5 min to dissolve, to obtain premix 1; (2) Mix polytetrafluoroethylene resin and 1,1,2,2-tetrafluoroethyl ethyl ether and stir at 300 r / min for 10 min to dissolve, to obtain premix 2; (3) Mix the silica microspheres with the remaining 1 / 2 of the total weight of organic solvent and stir and disperse at 300 r / min for 5 min to obtain premix 3; (4) After mixing and stirring premix 1 and premix 2 at a speed of 300 r / min for 5 min, add premix 3 and mix and stir at a speed of 300 r / min for 10 min to obtain mixture 4; (5) Add ethynylcyclohexanol, crosslinking agent, functionalized organosiloxane compound containing vinyl and epoxy groups, platinum catalyst and seroxac R77 to mixture 4 in sequence, and stir at 300 r / min for 5 min to obtain release coating liquid. (6) Apply the release coating liquid to the substrate layer and bake at 140°C for 50 seconds until the solvent evaporates completely to obtain the release film for foamed silicone.

[0028] Example 2 A release film for foamed silicone includes a substrate layer made of polyethylene terephthalate and a release coating layer. The release coating comprises the following raw materials in parts by weight: 800 parts of polydimethylsiloxane resin, 200 parts of polytetrafluoroethylene resin, 2000 parts of organic solvent, 100 parts of 1,1,2,2-tetrafluoroethyl ethyl ether, 30 parts of crosslinking agent, 5 parts of functionalized organosiloxane compound containing vinyl and epoxy groups, 20 parts of platinum catalyst, 10 parts of seroxac R77, 1 part of ethynylcyclohexanol, and 6 parts of silica microspheres. The organic solvent is a mixture of toluene, methyl ethyl ketone, No. 120 gasoline and ethyl acetate in a mass ratio of 1:1:1:1; the crosslinking agent includes the following raw materials in parts by weight: 20 parts of polymethylhydrosiloxane and 10 parts of polytetrafluoroethylene resin.

[0029] This embodiment also provides a method for preparing the release film for the above-mentioned foamed silicone, including the following steps: (1) Mix polydimethylsiloxane resin and 1 / 2 of the total weight of organic solvent and stir at 3000 r / min for 5 min to dissolve, to obtain premix 1; (2) Mix polytetrafluoroethylene resin and 1,1,2,2-tetrafluoroethyl ethyl ether and stir at 300 r / min for 10 min to dissolve, to obtain premix 2; (3) Mix the silica microspheres with the remaining 1 / 2 of the total weight of organic solvent and stir and disperse at 300 r / min for 5 min to obtain premix 3; (4) After mixing and stirring premix 1 and premix 2 at a speed of 300 r / min for 5 min, add premix 3 and mix and stir at a speed of 300 r / min for 10 min to obtain mixture 4; (5) Add ethynylcyclohexanol, crosslinking agent, functionalized organosiloxane compound containing vinyl and epoxy groups, platinum catalyst and seroxac R77 to mixture 4 in sequence, and stir at 300 r / min for 5 min to obtain release coating liquid. (6) Apply the release coating liquid to the substrate layer and bake at 140°C for 50 seconds until the solvent evaporates completely to obtain the release film for foamed silicone.

[0030] Example 3 A release film for foamed silicone includes a substrate layer made of polyethylene terephthalate and a release coating layer. The release coating comprises the following raw materials in parts by weight: 900 parts of polydimethylsiloxane resin, 100 parts of polytetrafluoroethylene resin, 2000 parts of organic solvent, 100 parts of 1,1,2,2-tetrafluoroethyl ethyl ether, 15 parts of crosslinking agent, 2 parts of functionalized organosiloxane compound containing vinyl and epoxy groups, 20 parts of platinum catalyst, 6 parts of seroxac R77, 1 part of ethynylcyclohexanol, and 2 parts of silica microspheres. The organic solvent is a mixture of toluene, methyl ethyl ketone, No. 120 gasoline and ethyl acetate in a mass ratio of 1:1:1:1; the crosslinking agent includes the following raw materials in parts by weight: 5 parts of polymethylhydrosiloxane and 10 parts of polytetrafluoroethylene resin.

[0031] This embodiment also provides a method for preparing the release film for the above-mentioned foamed silicone, including the following steps: (1) Mix polydimethylsiloxane resin and 1 / 2 of the total weight of organic solvent and stir at 3000 r / min for 5 min to dissolve, to obtain premix 1; (2) Mix polytetrafluoroethylene resin and 1,1,2,2-tetrafluoroethyl ethyl ether and stir at 300 r / min for 10 min to dissolve, to obtain premix 2; (3) Mix the silica microspheres with the remaining 1 / 2 of the total weight of organic solvent and stir and disperse at 300 r / min for 5 min to obtain premix 3; (4) After mixing and stirring premix 1 and premix 2 at a speed of 300 r / min for 5 min, add premix 3 and mix and stir at a speed of 300 r / min for 10 min to obtain mixture 4; (5) Add ethynylcyclohexanol, crosslinking agent, functionalized organosiloxane compound containing vinyl and epoxy groups, platinum catalyst and seroxac R77 to mixture 4 in sequence, and stir at 300 r / min for 5 min to obtain release coating liquid. (6) Apply the release coating liquid to the substrate layer and bake at 140°C for 50 seconds until the solvent evaporates completely to obtain the release film for foamed silicone.

[0032] Comparative Example 1 A release film for foamed silicone includes a substrate layer made of polyethylene terephthalate and a release coating layer. The release coating comprises the following raw materials in parts by weight: 1000 parts of polytetrafluoroethylene resin, 1100 parts of 1,1,2,2-tetrafluoroethyl ether, 15 parts of crosslinking agent, 3 parts of functionalized organosiloxane compound containing vinyl and epoxy groups, 20 parts of platinum catalyst, and 8 parts of seroxac R77. The crosslinking agent is polytetrafluoroethylene resin.

[0033] This embodiment also provides a method for preparing the release film for the above-mentioned foamed silicone, including the following steps: (1) Mix polytetrafluoroethylene resin and 1,1,2,2-tetrafluoroethyl ether and stir at 300 r / min for 10 min to dissolve them to obtain a premix; (2) Add crosslinking agent, functionalized organosiloxane compound containing vinyl and epoxy groups, platinum catalyst and seroxac R77 to the mixture in sequence, and stir at 300 r / min for 5 min to obtain release coating liquid. (3) Apply the release coating liquid to the substrate layer and bake at 140°C for 50 seconds until the solvent evaporates completely to obtain the release film for foamed silicone.

[0034] Experimental Example The performance of the foamed silicone release films prepared in Examples 1-3 and Comparative Example 1 was tested. The release force / residual adhesion rate was tested according to the national standard GB / T25256-2010 "Test Method for 180° Peel Force and Residual Adhesion Rate of Release Films for Optical Functional Films". The adhesion test involved cutting the prepared release film into 10cm*10cm samples, placing them in a 50℃ environment for 30 minutes, removing the samples, cooling them to room temperature, and observing whether the release layer exhibited peeling, detachment, or bubbling. The light transmittance / haze test was conducted according to the national standard GB / T 2410-2008 "Determination of Light Transmittance and Haze of Transparent Plastics". The appearance was assessed by visual inspection to determine if the film was smooth and even. The results are shown in Table 1.

[0035] Table 1. Test data of release film for foamed silicone.

[0036] As shown in Table 1, the formulation system of the embodiment outperforms traditional silicone release films in key indicators such as 20-minute release force, aging release force, and residual adhesion rate. Example 2 achieves a low release force range of 2.6-3.8 gf / 25 mm, which is 80% lower than the aging release force of 19.3 gf / 25 mm in Comparative Example 1, effectively solving the problem of silicone penetration and adhesion. At the same time, the release film for foamed silicone of the present invention improves the residual adhesion rate to 88.3% while maintaining a high light transmittance of 88.7%-89.8%, breaking through the industry bottleneck of easy reaction and penetration of ordinary silicone release films. In addition, its excellent release performance can meet the application requirements in the production and manufacturing of foamed silicone and has good market prospects.

[0037] The present invention has been described according to the above embodiments. It should be understood that the above embodiments do not limit the present invention in any way. All technical solutions obtained by equivalent substitution or equivalent transformation fall within the scope of the present invention.

Claims

1. A release film for foamed silicone, characterized in that, Includes the substrate layer and the release coating; The release coating comprises the following raw materials in parts by weight: 800-900 parts of polydimethylsiloxane resin, 100-200 parts of polytetrafluoroethylene resin, 1000-6000 parts of organic solvent, 50-200 parts of fluorinated solvent, 5-35 parts of crosslinking agent, 2-15 parts of anchoring agent, 10-30 parts of catalyst, 2-20 parts of release agent, 0.1-1.5 parts of inhibitor, and 1-10 parts of anti-sticking agent; The crosslinking agent comprises the following raw materials in parts by weight: 2-20 parts of polymethylhydrosiloxane and 3-15 parts of polytetrafluoroethylene resin.

2. The release film for foamed silicone as described in claim 1, characterized in that, The release coating comprises the following raw materials in parts by weight: 800 parts of polydimethylsiloxane resin, 200 parts of polytetrafluoroethylene resin, 2000-4000 parts of organic solvent, 100-150 parts of fluorinated solvent, 10-30 parts of crosslinking agent, 2-10 parts of anchoring agent, 15-25 parts of catalyst, 5-15 parts of release agent, 0.5-1 part of inhibitor, and 2-8 parts of anti-sticking agent; The crosslinking agent comprises the following raw materials in parts by weight: 5-20 parts of polymethylhydrosiloxane and 5-10 parts of polytetrafluoroethylene resin.

3. The release film for foamed silicone as described in claim 2, characterized in that, The release coating comprises the following raw materials in parts by weight: 800 parts of polydimethylsiloxane resin, 200 parts of polytetrafluoroethylene resin, 2000 parts of organic solvent, 100 parts of fluorinated solvent, 30 parts of crosslinking agent, 5 parts of anchoring agent, 20 parts of catalyst, 10 parts of release agent, 1 part of inhibitor and 6 parts of anti-sticking agent. The crosslinking agent comprises the following raw materials in parts by weight: 20 parts of polymethylhydrosiloxane and 10 parts of polytetrafluoroethylene resin.

4. The release film for foamed silicone as described in any one of claims 1 to 3, characterized in that, The substrate layer is made of polyethylene terephthalate; the organic solvent is at least one of toluene, methyl ethyl ketone, No. 120 gasoline, and ethyl acetate; the fluorinated solvent is tetrafluoroethyl solvent; the anchoring agent is a functionalized organosiloxane compound containing vinyl and epoxy groups; the catalyst is a platinum catalyst; the stripping agent is Dow 7201 and / or cyclohexanol R77; the inhibitor is ethynylcyclohexanol; and the anti-sticking agent is silica microspheres.

5. The method for preparing the release film for foamed silicone according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Dissolve polydimethylsiloxane resin in 1 / 2 of the total weight of organic solvent by stirring to obtain premix 1; (2) Dissolve polytetrafluoroethylene resin in a fluorinated solvent by stirring to obtain premix 2; (3) Stir and disperse the anti-sticking agent in the remaining 1 / 2 of the total weight of organic solvent to obtain premix 3; (4) After mixing and stirring premix 1 and premix 2, add premix 3 and mix and stir to obtain mixture 4; (5) Add inhibitor, crosslinking agent, anchoring agent, catalyst and release agent to mixture 4 in sequence, mix well to obtain release coating liquid; (6) Apply the release coating liquid to the substrate layer and bake to obtain the release film for foamed silicone.

6. The method for preparing a release film for foamed silicone as described in claim 5, characterized in that, In step (1), the stirring speed for dissolving is 2500~3500 r / min and the time is 2~6 min; in step (2), the stirring speed for dissolving is 250~350 r / min and the time is 5~15 min; in step (3), the stirring speed for dispersing is 250~350 r / min and the time is 2~6 min.

7. The method for preparing a release film for foamed silicone as described in claim 5, characterized in that, Step (4) includes the following steps: mixing and stirring premix 1 and premix 2 at a speed of 250~350 r / min for 2~6 min, then adding premix 3 and mixing and stirring at a speed of 250~350 r / min for 5~15 min to obtain mixture 4.

8. The method for preparing a release film for foamed silicone as described in claim 5, characterized in that, Step (5) The process includes the following steps: adding inhibitor, crosslinking agent, anchoring agent, catalyst and release agent to mixture 4 in sequence and stirring at a speed of 250~350 r / min for 2~6 min to obtain release coating liquid.

9. The method for preparing a release film for foamed silicone as described in claim 5, characterized in that, In step (6), the baking temperature is 130~150℃ and the time is 40~60s.

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