JP6287726B2 - Thermal insulation layer - Google Patents

Description

  The present invention relates to a heat insulating layer formed on a substrate.

  In industrial equipment and consumer equipment that require energy supply, various types of heat insulating materials have been conventionally used in order to increase energy efficiency, and research and development of heat insulating materials have been conducted. For example, in an automobile, in order to reduce engine cooling loss and increase its thermal efficiency, research and development of a heat insulating layer provided on a wall surface of a combustion chamber is underway. Recovery of waste heat from an exhaust system, an EGR cooler, or the like is also one of the important needs of automobiles. For this reason, an efficient heat insulating material is required.

  As a method of providing a heat insulating layer on the combustion chamber wall of the engine, conventionally, a method of forming a heat insulating layer by ceramic spraying has been studied, but since the sprayed layer is porous, a heat insulating layer is formed on the top surface of the piston or the like. In such a case, the penetration of the fuel becomes a problem, and the turbulence of the combustion gas flow due to the occurrence of cracks or the surface roughness becomes a problem.

  In contrast, the applicant of the present application has previously proposed a heat insulating layer described in Patent Document 1. Specifically, hollow particles surface-treated with a silane compound are contained in a silicone resin (tyranno compound), and the hollow particles are bonded to the silicone resin via the silane compound.

JP 2014-40818 A

  Although the heat insulating layer described in Patent Document 1 is useful, there is room for improvement so that, for example, in order to further reduce engine cooling loss, the thermal characteristics are more excellent. Specifically, it is improvement of heat resistance, reduction of thermal conductivity, and reduction of volume specific heat related to thermal responsiveness.

  Then, this invention makes it a subject to bring about the heat insulation layer which was improved in heat resistance, thermal conductivity, and volume specific heat, and was more excellent in thermal characteristics.

  In order to solve the above-mentioned problems, the present invention provides a heat-insulating layer containing a large number of hollow particles and a binder, the basic constituent unit of the silicone resin as the binder, a unit advantageous for improving heat resistance, thermal conductivity, and Units advantageous for reducing the volume specific heat were included.

That is, the heat insulating layer presented here is formed on the surface of the base material of the parts constituting the engine combustion chamber, and a number of hollow particles and a binder that fills the space between the hollow particles and holds the hollow particles on the base material. relates insulation layer with said binder, Ri silicone resins der containing the T units and D units as basic unit, the amount of T units to total amount of the T units and D units than 75 mol% 95 mol% It is characterized by the following.

  The T unit and D unit, which are basic structural units of the silicone resin according to the present invention, are shown in the following formulas (1) and (2), respectively.

  In general, the basic structural unit of a silicone resin includes a Q unit having no substituent and an M unit having three substituents in addition to the T unit and D unit.

  Since the heat resistance of the silicone resin is derived from the Si—O bond siloxane skeleton, the heat resistance of the silicone resin is improved as the number of T unit crosslinked structures increases. However, if there are too many T units, a high-density and strong three-dimensional network structure is formed at the time of film formation, so that the thermal conductivity due to lattice vibration or the like increases. Moreover, since the formed film lacks flexibility, voids and cracks are likely to occur.

  Therefore, by placing a D unit linear structure in this three-dimensional network structure, lattice vibration is suppressed and a minute space is formed between adjacent main chains, so that the thermal conductivity and volume of the silicone resin are reduced. Specific heat can be reduced.

  Therefore, in the present invention, the silicone resin, which is the base material of the heat insulating layer, includes the T unit and the D unit, thereby improving the heat resistance while further improving the heat resistance as compared with the heat insulating layer described in Patent Document 1. A heat insulating layer with reduced rate and volume specific heat can be formed. In addition, since flexibility is generated in the formed film, internal stress at the time of film formation (firing, heat curing) of the heat insulating layer is relieved, and voids and cracks are hardly generated in the film, thereby improving the film formability.

In addition, the substituents R ₁ , R ₂ and R ₃ in the formula (1) and the formula (2) may be the same or different, and may be an alkyl group, an aryl group, an alkoxy group, a phenol group, a vinyl group, It is a substituent selected from the group consisting of hydrogen, a hydrosilyl group, an alkoxysilanol group, or a halogen-substituted hydrocarbon group in which some or all of the hydrogen atoms bonded to these carbon atoms are substituted with a halogen atom.

Then, the amount of T units to total amount of the T and D units is Ru der less 75 mol% or more 95 mol%. Thereby, while being excellent in heat resistance, heat conductivity and volume specific heat are reduced, and the heat insulation layer which is hard to produce a void and a crack can be obtained more effectively.

In addition, as the hollow particles, a Si-based oxide component (for example, silica (SiO ₂ )) or an Al-based oxide component (for example, alumina (Al ₂ ) such as a silica balloon, a glass balloon, a shirasu balloon, a fly ash balloon, and an airgel balloon. It is preferable to employ ceramic hollow particles containing ₂ O ₃ )). And it is preferable that the said hollow particle is contained at least 45 vol% in the said heat insulation layer.

  The heat-insulating layer preferably has a surface roughness Ra of 5 μm or less. Thereby, when the said heat insulation layer is formed in the base-material surface of the components which comprise an engine combustion chamber, disturbance of a combustion gas flow decreases and it becomes advantageous to the improvement of combustibility.

  As described above, according to the present invention, it is possible to form a heat insulating layer with reduced thermal conductivity and volume specific heat while improving the heat resistance of the heat insulating layer. In addition, since flexibility is generated in the formed film, internal stress during film formation (firing, heat curing) of the heat insulating layer is relieved, cracks are less likely to occur in the film, and film formability is improved.

FIG. 1 is a cross-sectional view of an engine as an application example of the present invention. FIG. 2 is a cross-sectional view showing a heat insulating layer on the piston top surface of the engine. FIG. 3 is a graph showing the thermogravimetric change of the binder. FIG. 4 is a graph showing the thermal conductivity of the binder. FIG. 5 is a graph showing the volume specific heat of the binder.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or its application.

  In FIG. 1, 1 is an aluminum alloy piston as a base material on which a heat insulating layer is formed, 2 is a cylinder block, 3 is a cylinder head, 4 is an intake valve for opening and closing the intake port 5 of the cylinder head 3, and 6 is an exhaust port. An exhaust valve 7 opens and closes, and 8 is a fuel injection valve. The combustion chamber of the engine is formed by the top surface of the piston 1, the cylinder block 2, the cylinder head 3, and the front surface of the umbrella portion of the intake / exhaust valves 4 and 6 (surface facing the combustion chamber). A cavity 9 is formed on the top surface of the piston 1. Note that the illustration of the spark plug is omitted.

  As shown in FIG. 2, a heat insulating layer 11 is formed on the top surface of the piston 1. The heat insulating layer 11 is a silicone resin that holds a large number of hollow particles 12 made of an inorganic oxide and a base material (matrix) of the heat insulating layer 11 by filling the space between the hollow particles 12 and holding the hollow particles 12 on the piston 1. System binder 13.

As the hollow particles 12, Si-based oxide components (for example, silica (SiO ₂ )) or Al-based oxide components (for example, alumina (Al ₂ )) such as silica balloons, glass balloons, shirasu balloons, fly ash balloons, and airgel balloons. It is preferable to employ ceramic hollow particles containing O ₃ )). In addition, it is preferable that the hollow particle 12 is contained at least 45 vol% in the heat insulation layer. The average particle size of the hollow particles 12 is preferably 20 μm or more and 30 μm or less, for example. However, this numerical range is a preferable range when the heat insulating layer 11 is provided on the wall surface of the combustion chamber of the engine, and is not limited.

  Next, the binder 13 according to the present invention will be described in detail.

  3-5 has shown the result of having measured the thermogravimetric change, thermal conductivity, and volume specific heat about three types of binders, ie, a silicate glass, Tyrannovarnish, and a binder of a present Example, respectively.

  Silicate glass is composed of only T units as a basic structural unit, and contains inorganic fibers as a reinforcing material. In addition, Tyrannovarnish is a xylene / 1- 1 having a concentration of 45.7% by weight of a mixture of polytitanocarbosilane (47.4% by weight) and methylsiloxane polysiloxane (52.6% by weight) which is a polysiloxane compound. A butanol solution (VN-100, manufactured by Ube Industries, Ltd.), which has been conventionally used as a binder. The binder of this example is a silicone resin according to the present invention, and the amount of T unit relative to the total amount of T unit and D unit is 90 mol% (manufactured by Shin-Etsu Chemical Co., Ltd., KR251).

  As shown in FIG. 3, when measuring the thermogravimetric change of the Tyranno varnish conventionally used as a binder, it was found that the weight retention rate decreased to about 0.7 at about 700 ° C. This is considered to be because there are few T units of methylphenyl polysiloxane contained in Tyrannovarnish, and it turns out that heat resistance is low. On the other hand, when a thermogravimetric change was measured about the silicate glass which consists only of T units, it turned out that a weight maintenance factor maintains the value of 0.9 or more also at about 700 degreeC. From the above, it is considered that the heat resistance of the binder improves as the number of T units increases.

  However, as shown in FIGS. 4 and 5, silicate glass has a higher thermal conductivity and a larger volume specific heat than Tyrannovarnish. This is considered to be because when there are too many T units, a high-density and strong three-dimensional network structure is formed at the time of film formation, and the thermal conductivity due to lattice vibration or the like increases.

  Therefore, when a silicone resin containing 90 mol% T unit and 10 mol% D unit is used as the binder of this example, the weight retention rate is maintained at approximately 0.9 even at about 700 ° C. as shown in FIG. It can be seen that it is comparable to silicate glass.

  Moreover, as shown in FIG.4 and FIG.5, heat conductivity was comparable as a Tyranno varnish, and it turned out that a volume specific heat takes the value further reduced rather than the Tyranno varnish. This is because the linear vibration of the D unit enters the three-dimensional network structure formed by the T unit, thereby suppressing lattice vibration and forming a micro space between the adjacent main chains. It is considered that the rate and specific heat of volume have decreased.

  As described above, the present invention is characterized in that the binder 13 is a silicone resin including T units and D units as basic structural units.

  Thereby, it is possible to form a heat insulating layer having a low thermal conductivity and a small volume specific heat while improving the heat resistance as compared with the conventional binder. Moreover, since flexibility is generated in the formed film, internal stress at the time of film formation (firing, heat curing) of the heat insulating layer is relieved, cracks are hardly generated in the film, and the formation of the film can be improved.

  In this embodiment, it is preferable that the proportion of T units contained in the binder of the present embodiment is larger than the proportion of D units. In particular, the amount of T units relative to the total amount of T units and D units is preferably 75 mol% or more and 95 mol% or less. Thereby, while being excellent in heat resistance, heat conductivity and volume specific heat are reduced, and the heat insulation layer which is hard to produce a void and a crack can be obtained more effectively.

<Formation of heat insulation layer>
As the binder 13, the silicate glass and the binder of this example were used, and the heat insulating layer 11 was formed by the following method.

A heat insulating material for forming the piston 1 and the heat insulating layer 11 is prepared. About the piston 1, the recessed part for cavity formation is formed in the top surface, and stain | pollution | contamination, such as oil and fingerprint adhering to the top surface of the piston 1, is removed by a degreasing process. In addition, a heat insulating material obtained by stirring and mixing the binder 13 and the hollow particles 12 is prepared. If necessary, a thickener or a dilution solvent is added to adjust the viscosity of the heat insulating material. In order to increase the adhesion between the piston 1 and the heat insulating material, particularly the silicone resin, it is preferable that the top surface of the piston 1 is roughened. As the roughening treatment, for example, blasting such as sand blasting is preferably performed. For example, the blasting process can be performed using an air blasting apparatus, using alumina having a particle size of # 30 as an abrasive, and processing conditions of a pressure of 0.39 MPa, a time of 45 seconds, and a distance of 100 mm. In addition, not only this but when the piston 1 consists of Al alloy, you may make it form a micro unevenness | corrugation in the top surface of the piston 1 by an alumite process. For example, the alumite treatment can be performed using an oxalic acid bath under a treatment condition of a bath temperature of 20 ° C., a current density of 2 A / dm ² , and a time of 20 minutes.

  Thereafter, the heat insulating material is applied to the top surface of the piston 1 using a spray or a brush. If necessary, the coating is repeated (overcoated) to obtain a desired coating thickness. Subsequently, the applied heat insulating material is preliminarily dried by hot air drying, an infrared heater or the like. Alternatively, as one form of application, a heat insulating material is placed on the top surface of the piston body 1, and the heat insulating material is pressed against the piston top surface by a molding die having a molding surface that follows the shape of the piston top surface, and spread over the entire top surface. Good. The coating thickness of the heat insulating material is, for example, 40 μm or more and 100 μm or less.

  Next, the heat insulating material applied to the piston top surface is subjected to a heat treatment for several hours to several tens of hours at a temperature of about 180 ° C., for example. Thereby, the binder 13 hardens | cures, many hollow particles 12 are filled closely, and the heat insulation layer 11 with which these particles were filled with the binder 13 is obtained.

<Surface roughness of the heat insulation layer>
About the heat insulation layer 11 formed by the said method, surface roughness Ra was calculated | required from the roughness curve measured after grinding | polishing. The results are shown in Table 1.

  As shown in Table 1, when silicate glass is used as the binder 13, the surface roughness Ra has a high value of 7.2 μm. This is thought to be because a lot of voids and cracks are generated because the flexibility of the film is poor, and as a result, the surface roughness is increased even after polishing.

  On the other hand, when the binder of the present embodiment according to the present invention is used as the binder 13, the surface roughness Ra is as low as 2.3 μm. This is considered to be due to the use of the binder of this example, which improves the flexibility of the film and suppresses the generation of voids and cracks, and as a result, the surface roughness is also suppressed.

  Therefore, by using the binder of the present embodiment as the binder 13, the surface roughness Ra of the heat insulating layer can be set to 5 μm or less. Thereby, when the said heat insulation layer 11 is formed in the cavity 9 surface of the top surface of the piston 1, disturbance of a combustion gas flow is reduced and it becomes advantageous to the improvement of combustibility.

  In addition, since the heat insulation layer 11 according to the present invention has an advantage that voids and cracks are less likely to occur, not only the top surface of the piston 1, but also other substrate surfaces of parts constituting the engine combustion chamber, specifically, For example, it can also be formed on a portion having a relatively large area such as the inner peripheral surface of the cylinder liner or the lower surface of the cylinder head 3.

  The present invention can form a heat insulating layer with low thermal conductivity and small volume specific heat while improving the heat resistance of the heat insulating layer, and it is difficult for voids and cracks to occur in the film, thereby improving the film formability. So it is extremely useful.

1 Piston (base material)
11 Heat insulation layer 12 Hollow particles 13 Binder

Claims (3)

A heat insulating layer formed on the surface of a base material of a component constituting an engine combustion chamber, and comprising a large number of hollow particles, and a binder that fills the space between the hollow particles and holds the hollow particles on the base material,
The binder is, Ri silicone resins der containing the T units and D units as basic unit,
The heat insulating layer, wherein the amount of T unit relative to the total amount of T unit and D unit is 75 mol% or more and 95 mol% or less . Oite to claim 1,
The heat insulating layer, wherein the hollow particles are contained at least 45 vol% in the heat insulating layer. In claim 1 or claim 2 ,
The heat insulation layer characterized by surface roughness Ra of the said heat insulation layer being 5 micrometers or less.

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