JP2018064039A - Thermal shield film for electronic circuit protection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal shield film for electronic circuit protection.SOLUTION: A thermal shield film for electronic circuit protection comprises: a resin layer including a resin composition and voids. The resin layer is 50 μm or larger in thickness; and the number of voids per 100 μm of the thickness in a thickness direction is 50-500 /100 μm.SELECTED DRAWING: None

Description

  The present invention relates to a thermal barrier film for protecting an electronic circuit.

In recent years, with the development of communication technology, electronic circuits having various communication functions have been used in various environments. However, since such an electronic circuit leads to circuit destruction at high temperatures, it is necessary to protect the electronic circuit with a heat shielding material depending on the environment. For example, a resin casing for a communication electronic circuit used outdoors such as a smart grid is required to have a function of shielding heat derived from sunlight or the like.
Conventionally, various heat shielding materials have been studied (for example, Patent Documents 1 to 3). However, the use of metal-based heat shielding materials for the purpose of protecting electronic circuits is difficult due to problems such as difficulty in transmitting and receiving radio waves. It can be difficult.

JP 2000-129172 A JP 2014-28896 A JP 2004-34383 A

In view of the above problems, an object of the present invention is to provide a thermal barrier film for an electronic circuit having excellent thermal barrier properties.
A desirable object of the present invention is to provide a heat-shielding film for an electronic circuit that can hardly be used for communication and can be used for, for example, a communication electronic circuit.

As a result of intensive studies, the present inventors have found that the film has voids and exhibits excellent heat shielding properties by setting the void frequency within a specific range, and have reached the present invention.
That is, the present invention employs the following configuration.

1. A film comprising a resin composition and having a resin layer containing voids, wherein the resin layer has a thickness of 50 μm or more, and the number of voids per 100 μm thickness in the thickness direction is 50 to 500/100 μm. A thermal barrier film for protecting electronic circuits.
2. 2. The heat shielding film for protecting an electronic circuit according to 1, wherein the resin layer has 50 to 500/100 μm of voids having a height of 0.1 to 5.0 μm per 100 μm thickness in the thickness direction.
3. 3. The heat shielding film for protecting an electronic circuit according to the above 1 or 2, which is used for protecting an electronic circuit for communication.

ADVANTAGE OF THE INVENTION According to this invention, the thermal insulation film which has the outstanding thermal insulation property can be provided. Therefore, the thermal barrier film of the present invention can be suitably used for applications that protect electronic circuits.
Moreover, since the heat-insulating film of the present invention hardly inhibits communication, it can be suitably used for the purpose of protecting electronic circuits for communication, for example.
More specifically, the heat-shielding film of the present invention can be used, for example, by being attached to a resin casing, and by doing so, a resin casing having a heat-shielding property is obtained. The internal electronic circuit can be protected.

It is a schematic diagram showing the arrangement | positioning in evaluation of heat-insulating property. It is an example of the cross-sectional SEM image of a resin layer.

(Heat shield film)
The thermal barrier film of the present invention is a film having a resin layer made of a resin composition and containing voids. Here, the void is a void. The resin layer has a thickness of 50 μm or more, and has 50 to 500/100 μm voids per 100 μm thickness in the thickness direction.

The heat insulating film of the present invention may be a single layer film composed only of the resin layer, or may be a laminated film having the resin layer and another layer. From the viewpoint of coexistence of a void mode suitable for obtaining higher heat-shielding properties and production stability during film formation (hereinafter sometimes referred to as film-forming property), the above resin layer, that is, this is relatively It is a layer containing many voids (hereinafter sometimes referred to as a void layer), and as this and other layers, a layer containing relatively few voids or no voids (hereinafter sometimes referred to as a support layer). Are preferred.
It should be noted that “heat insulation” in the present invention is not limited to not having a heat insulation function.

(Resin layer)
The resin constituting the resin composition of the resin layer in the present invention is particularly preferably a thermoplastic resin, and examples thereof include polyester, polyolefin, polystyrene, and acrylic. From the viewpoint of obtaining a film having excellent mechanical properties and thermal stability, polyester is preferred.

  When using polyester as resin, it is preferable to use polyester which consists of a dicarboxylic acid component and a diol component as this polyester. Examples of the dicarboxylic acid component include components derived from terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, adipic acid, and sebacic acid. Examples of the diol component include components derived from ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and 1,6-hexanediol. Among these polyesters, aromatic polyesters are preferable from the viewpoint of heat resistance, and polyethylene terephthalate is particularly preferable.

  The polyester may be a homopolyester, but is preferably a copolyester from the viewpoint of superior workability when bonded to a housing or the like. As such a copolyester, copolyethylene terephthalate is preferred. Further, by using the copolymer polyester, excellent film forming properties can be ensured even if a relatively large number of voids are included. When using a laminated film having a void layer and a support layer as the heat-shielding film, it is effective to improve the film-forming property by using a copolymer polyester as the polyester used for the void layer containing a relatively large amount of voids. It is preferable. The ratio of the copolymerization component is, for example, 1 to 20 mol%, preferably 3 to 15 mol%, more preferably 5 to 13 mol%, based on 100 mol% of all dicarboxylic acid components. By setting the proportion of the copolymer component within this range, excellent film forming properties can be obtained even if a relatively large amount of voids is contained. Moreover, the film excellent in thermal dimensional stability can be obtained. In addition, as a copolymerization component, the dicarboxylic acid component and diol component which were illustrated above can be mentioned. A particularly preferred copolymerized polyester is isophthalic acid component copolymerized polyethylene terephthalate.

  In addition, when it is desired to provide functions such as heat resistance or ultraviolet resistance other than heat shielding, antifouling resistance, etc., within a range not impairing the object of the present invention, it is applied to the film surface by a known method according to the purpose. The coating layer can be formed by coating, or an additive capable of adding the above function to the inside of the film can be added.

(void)
Since the heat-shielding film of the present invention has a heat-shielding property, the number of voids in the thickness direction per 100 μm thickness of the resin layer needs to be 50 to 500/100 μm. When there are too few voids, the heat shielding effect due to the presence of voids is reduced, so that the heat shielding property is lowered. From this viewpoint, the number of voids is preferably 100/100 μm or more, more preferably 150/100 μm or more, and further preferably 200/100 μm or more. On the other hand, even if there are too many voids, there will be too many voids and the heat shielding properties will be reduced. Moreover, it exists in the tendency for a film to be easy to fracture | rupture and to become difficult to obtain a film. From this point of view, the number of voids is preferably 480/100 μm or less, more preferably 470/100 μm or less, further preferably 450/100 μm or less, and particularly preferably 420/100 μm or less.

  The number of voids is preferably the number of voids having a void size in the film thickness direction (hereinafter sometimes referred to as void height) of 0.1 to 5.0 μm. By doing in this way, the heat-shielding improvement effect can be heightened more. This is because voids that are too small or too large tend not to exhibit the effect of improving heat shielding properties due to the presence of voids. Furthermore, it is preferable to satisfy the above number for voids having a height of 0.2 to 3.0 μm.

Although it is not limited to this, the following mechanisms can be considered that the heat insulation effect is show | played by the said aspect. That is, it is considered that the number and height of voids as described above increase the reflectance in the infrared region and decrease the thermal conductivity of the film itself. Therefore, if the number of voids is small, the reflectance in the infrared region tends to decrease, and the thermal conductivity tends not to decrease. On the other hand, when the number of voids is large to some extent, the heat shielding property tends to be improved, but when it is too much, the heat shielding property tends to be lowered and the film tends to be difficult to obtain. Further, when the height of the void is appropriate, the reflectance in the infrared region tends to be more suitably increased.
Since the present invention exhibits heat shielding properties by voids in this way, it is difficult to inhibit transmission of electromagnetic waves for communication.

  The resin layer in the present invention contains voids, but in order to form voids, the resin is incompatible with inorganic particles, organic particles, organic-inorganic composite particles, or resins constituting the resin layer as void nucleating agents. (Hereinafter, sometimes referred to as incompatible resin). That is, by stretching a resin composition obtained by adding a void nucleating agent to a resin, a method of peeling the interface between the resin and the void nucleating agent to form a void can be used. Moreover, the method of forming a void using a supercritical method by a batch type etc. can also be used. From the viewpoint of simplicity and productivity, the former method of forming a stretched film to which a void nucleating agent is added is preferable because a void can be continuously formed by adopting a stretching method using a stenter or the like.

As the void nucleating agent, various known void nucleating agents can be employed. When the resin is a polyester resin, barium sulfate, calcium carbonate, silicon dioxide and the like are preferable as the inorganic particles. As the incompatible resin, poly-4-methylpentene-1, olefin resins such as polypropylene, polystyrene, and the like can be used, which is preferable.
In the method using a void nucleating agent, the amount of void can be increased or decreased by increasing or decreasing the amount of the void nucleating agent, and the size of the void is adjusted by adjusting the size of the void nucleating agent or the draw ratio. be able to. Even in the supercritical process, the amount and size of voids can be adjusted by adjusting the amount, temperature and pressure of the blowing agent. Moreover, a void can be crushed by pressing a film and the height of a void can also be adjusted low.

(Film thickness)
In the heat shielding film of the present invention, the resin layer has a thickness of 50 μm or more in order to obtain excellent heat shielding properties. If it is too thin, the number of voids will definitely decrease and it will be difficult to achieve excellent heat shielding properties. On the other hand, if it is too thick, it may be difficult to handle or process, or it may be excessive quality. Accordingly, the thickness of the film is preferably 50 to 500 μm, more preferably 75 to 400 μm, and still more preferably 100 to 350 μm.
The thickness of the thermal barrier film of the present invention is the same as the preferred thickness of the resin layer in the case of a single layer film. In the case of a laminated film, the thickness is preferably 100 to 500 μm, more preferably 150 to 350 μm, and still more preferably 200 to 250 μm.

When the heat-shielding film of the present invention has a resin layer and a support layer, the thickness of each layer may be set in consideration of film forming properties and void formation. That is, the film-forming property tends to be improved by making the support layer relatively thick. On the other hand, the thickness of the resin layer tends to make it easy to obtain a suitable void mode of the present invention. From the viewpoint of these balances, when the total thickness of the resin layer and the support layer is 100%, the resin layer preferably has a thickness ratio of 50 to 95%, more preferably 60 to 90%. Good. Further, the thickness of the support layer is preferably 50 to 5%, more preferably 40 to 10%.
The laminated structure of the resin layer and the support layer is a two-layer structure of resin layer / support layer, a three-layer structure of resin layer / support layer / resin layer or support layer / resin layer / support layer, or four layers in the same manner. The laminated structure described above may be used. Particularly preferred is a three-layer structure of support layer / resin layer / support layer from the viewpoints of film forming properties, curling, and the like.

(Production method)
Hereinafter, an example of the method for producing the thermal barrier film of the present invention will be described. In this example, a laminated film is used as the heat shield film. Note that the film forming machine axis direction may be referred to as a vertical direction, a longitudinal direction, or MD. In addition, a direction perpendicular to the film forming machine axis direction and the thickness direction may be referred to as a lateral direction, a width direction, or TD.

  For example, a polyester composition is used as the resin composition used for the heat shielding film. Such a polyester composition contains, for example, barium sulfate particles as a void nucleating agent in polyester as a thermoplastic resin constituting the film. The resin composition may further be a composition containing any other void nucleating agent. Moreover, about the thing used for a support layer, it can have no void nucleating agent. The resin composition is preferably filtered using a nonwoven fabric type filter having an average opening of 10 to 100 μm, preferably an average opening of 20 to 50 μm, and made of stainless steel fine wires having a wire diameter of 15 μm or less. By performing this filtration, it is possible to suppress aggregation of particles that normally tend to aggregate into coarse aggregated particles, and to suppress formation of coarse voids. Thus, a resin composition for forming the resin layer and a resin composition for forming the support layer are obtained.

Each filtered resin composition is extruded in a multilayer state from a die by a simultaneous multilayer extrusion method using a feed block in a molten state to produce a laminated unstretched sheet.
The laminated unstretched sheet extruded from the die is cooled and solidified by a casting drum to form a laminated unstretched film. This laminated unstretched film is heated by roll heating, infrared heating or the like, and stretched in the longitudinal direction to obtain a laminated longitudinally stretched film. This stretching is preferably performed by utilizing the difference in peripheral speed between two or more rolls. The longitudinal stretching is preferably performed at a temperature equal to or higher than the glass transition point (Tg) of the polyester of the resin layer. More preferably, it is the range of Tg or more and (Tg + 70 ° C.) or less. The draw ratio in the machine direction is preferably 2.2 to 4.0 times, more preferably 2.3 to 3.9 times. If it is less than 2.2 times, the thickness unevenness of the film tends to deteriorate, and if it exceeds 4.0 times, breakage tends to occur during film formation. After longitudinal stretching, it is also possible to apply a coating liquid here to give a function.

  The laminated film after the longitudinal stretching is successively subjected to preheating, transverse stretching, heat setting, and thermal relaxation to form a laminated biaxially oriented film. These processes are performed while the film is running. The transverse stretching process starts from a temperature higher than Tg. Although the temperature rise in the transverse stretching process may be continuous or stepwise (sequential), the temperature is usually raised sequentially. For example, the transverse stretching zone of the tenter is divided into a plurality along the film running direction, and the temperature is raised by flowing a heating medium having a predetermined temperature for each zone. The transverse stretching is preferably performed at a temperature of (Tg + 5 ° C.) to (Tg + 50 ° C.) with respect to the glass transition point (Tg) of the polyester of the resin layer. The draw ratio in the transverse direction is preferably 2.5 to 4.5 times, more preferably 2.8 to 3.9 times. If it is less than 2.5 times, the thickness unevenness of the film tends to deteriorate, and if it exceeds 4.5 times, breakage tends to occur during film formation. Moreover, the thermal dimensional stabilization of the film is also excellent by heat-setting after the stretching ratio and stretching. Such heat setting can be preferably performed at a temperature of (Tm-50 ° C) to (Tm-10 ° C) for 5 to 60 seconds with respect to the melting point (Tm) of the polyester of the resin layer.

(Heat insulation)
The heat shielding film of the present invention has a heat shielding property described later of preferably 50 ° C. or lower, more preferably 48 ° C. or lower, and further preferably 46 ° C. or lower.

(Use)
The heat-shielding film of the present invention is used for the purpose of protecting an electronic circuit from heat applied in the environment in which it is used. For example, the heat given from sunlight outdoors is shielded to prevent the electronic circuit from being destroyed. Specifically, for example, there may be a mode in which the electronic circuit is partially or entirely covered with the heat-shielding film of the present invention.

As a more preferred embodiment, the electronic circuit is housed in a housing, and the heat shielding film of the present invention is used in the housing. For example, there may be an embodiment in which such a case is manufactured using the heat-shielding film of the present invention, or the heat-shielding film of the present invention is bonded to the surface of the case. Here, since the housing is a metal housing, communication is hindered. Therefore, when the electronic circuit is a communication electronic circuit, a non-metal, for example, wooden or resin housing is preferable, and a resin housing is particularly preferable. The case (resin case) is preferable.
The heat shielding film of the present invention can be bonded to the housing using, for example, an adhesive.

The thermal barrier film of the present invention is particularly suitably used for smart meters. The smart meter is a next-generation watt-hour meter that measures power digitally and has a communication function in the meter, unlike a conventional analog inductive watt-hour meter. Data measured by the communication function can be transmitted. Here, the electric meter is mainly called a smart meter, but includes a similar measuring instrument such as gas or water. It is suitable mainly for smart grids (English: smart grid) and the like that utilize their communication functions to perform automatic meter reading that does not include meter reading by humans, and are expected to be applied to various services.
In addition, the heat-shielding film of the present invention can be used for automobile applications, building material applications, packaging applications, and the like by utilizing the heat-shielding effect.

Hereinafter, the present invention will be described in detail by way of examples. Each characteristic value was measured by the following method.
(1) Number of Voids, Void Height Using a focused ion / electron beam processing device (FIB-SEM) (S5200, manufactured by Hitachi High-Tech Fielding Co., Ltd.), performing GaB beam irradiation and FIB processing, SEM image of film cross section Get. SEM images were obtained at a magnification of 20,000 times for each of three images at arbitrary positions on the cross section parallel to the MD direction of the film and the cross section parallel to the TD direction. At this time, the outermost surface of the film was prevented from entering the SEM image. In the case of a laminated film, an SEM image of the resin layer was obtained so that the support layer did not enter. In addition, when the sample was set in the apparatus, the vertical direction of the photograph was made parallel to the thickness direction of the film.

In each SEM image, a straight line (21) is drawn in the center in the width direction in parallel with the film thickness direction, and one film is formed on the left and right in the center between the center straight line and the width direction end (23) of the photograph. A straight line (22) was drawn parallel to the direction, and a total of three straight lines parallel to the thickness direction were drawn (see FIG. 2).
The number of voids that overlap the straight line entered above and whose height in the thickness direction is 0.1 to 5.0 μm is counted, and all data in the MD direction and TD direction (MD direction From three SEM images, the average value of data for three straight lines and three SEM images in the TD direction, respectively, and three straight lines for each, a total of 18 data) is calculated. The thickness was taken as the thickness, and the number of voids per 100 μm length (pieces / 100 μm) was calculated.
Here, the height of the void is the height of the void where the void and the straight line overlap. Moreover, the size was calculated | required with the scale in a SEM image.

(2) Film thickness, thickness of each film layer A film sample was cut into a triangle, fixed to an embedded capsule, and then embedded with an epoxy resin. And after making the cross section parallel to a vertical direction into a thin film section with a microtome (ULTRACUT-S), the film sample which was embedded was observed and photographed using the optical microscope, the thickness ratio of each layer was measured from the photograph, and the whole film The thickness of each layer was calculated from the thickness ratio of each layer.

(3) Heat shielding property As shown in FIG. 1, an evaluation sample (12) of A3 size was placed at a position 9 cm from a halogen lamp (JDR110V / 40WLM / K50W Type manufactured by USHIO LIGHTING) (11), and its back surface (with a halogen lamp A3 size, 2mm thick polycarbonate plate (13) is aligned and in contact with the opposite side), and the back side (the opposite side of the halogen lamp), A5 size at 9.5cm from the halogen lamp Black paper (thickness 0.25 mm) (14) was placed in the center of the evaluation sample and polycarbonate plate. Furthermore, a thermography (15) is arranged on the back side so that the temperature change at the center of the back side of the black drawing paper (the side opposite to the halogen lamp) can be measured.
The temperature at the center of the black drawing paper 10 minutes after the halogen lamp irradiation was read by thermography, and this value was used as the evaluation result of the heat shielding property. The measurement was performed in a room with a room temperature of 25 ° C. and a relative humidity of 50 ± 10%.

[Example 1]
(Production of barium sulfate particles 1)
330 kg of black roasted barium sulfide (also called black ash) and 1000 L of water are placed in a reaction vessel, and while stirring, an equivalent amount of 9 molar hydrochloric acid is added to barium chloride, followed by stirring. Aeration was performed, and the insoluble residue was separated by filtration to obtain 1300 L of a 1.2 molar aqueous barium chloride solution as barium chloride. The solution was kept at 45 ° C., and 95 L of 18 molar sulfuric acid was added, followed by stirring for 4 hours, the resulting suspension was filtered, and the resulting hydrous cake was washed with water and dried to give 400 kg of barium sulfate particles. 1 was obtained. When 100 barium sulfate particles 1 were arbitrarily selected and the average size of SEM images taken at a magnification of 20000 using a scanning electron microscope (S5200 manufactured by Hitachi High-Tech Fielding) was calculated, the obtained barium sulfate particles 1 were obtained. The average particle size was 1.2 μm.

(Manufacture of polyester)
132 parts by mass of dimethyl terephthalate, 18 parts by mass of dimethyl isophthalate (12 mol% with respect to the total acid component of the polyester), 96 parts by mass of ethylene glycol, 3.0 parts by mass of diethylene glycol, 0.05 parts by mass of manganese acetate Then, 0.012 parts by mass of lithium acetate was charged into a rectification column and a flask equipped with a distillation condenser, and heated to 150 to 235 ° C. with stirring to distill methanol to conduct a transesterification reaction. After methanol was distilled, 0.03 parts by mass of trimethyl phosphate and 0.04 parts by mass of germanium dioxide were added, and the reaction product was transferred to the reactor. Then, while stirring, the pressure in the reactor was gradually reduced to 0.5 mmHg, and the temperature was raised to 290 ° C. to carry out a polycondensation reaction to obtain a copolyester.

(Film production)
The copolymer polyester obtained above was used for the resin layer (referred to as layer A), and the barium sulfate particles 1 obtained above were added so as to have the contents shown in Table 1 to obtain the raw material of layer A. In addition, the above-described copolymer polyester was used for the support layer (referred to as layer B), and the barium sulfate particles 1 obtained above were added so as to have the contents shown in Table 1 to obtain the raw material for layer B. .
Feed to two extruders each heated to 280 ° C., and feed the layer A raw material and the layer B raw material into a layer B / layer A / layer B structure and a thickness ratio shown in Table 1 in a three-layer feed block They were merged using an apparatus, and formed into a sheet form from a die while maintaining the laminated state. Further, this sheet was cooled and solidified with a cooling drum having a surface temperature of 25 ° C., and the obtained unstretched film was stretched in the machine direction at a magnification of 3.0 times at a temperature of 90 ° C. and cooled with a roll group at 25 ° C. Subsequently, both ends of the film were guided to a tenter while being held with clips, and stretched in the transverse direction at a magnification of 3.7 times in an atmosphere heated to 120 ° C. while preheating in a preheating zone. Thereafter, heat setting was performed at a temperature of 190 ° C. in a tenter, longitudinal relaxation was 1.5%, lateral width was 2%, and the mixture was cooled to room temperature to obtain a biaxially stretched film. The evaluation results of the obtained film are shown in Table 1.

[Example 2]
(Production of barium sulfate particles 2)
In the production of the barium sulfate particles 1 in Example 1, the stirring reaction time for 4 hours was shortened to 3 hours, and the suspension was filtered. The average particle diameter of the obtained barium sulfate particles 2 was 0.7 μm.

(Film production)
A biaxially stretched film was obtained in the same manner as in Example 1 except that such barium sulfate particles 2 were used. The evaluation results are shown in Table 1.

[Example 3]
(Production of calcium carbonate particles 1)
Quick lime obtained by firing limestone was dissolved in water to form a slaked lime slurry, and reacted with carbon dioxide to synthesize calcium carbonate. The calcium carbonate aqueous slurry was subjected to foreign matter and coarse particle removal with a sieve, and then the calcium carbonate aqueous slurry was subjected to particle growth by Ostwald ripening to obtain calcium carbonate particles.
Next, 2% by mass of trimethyl phosphate is added to the calcium carbonate solid content to surface-treat, then dehydrated, dried and crushed, and the resulting dry powder is classified with an air classifier and surface-treated. Calcium carbonate particles 1 were obtained. The average particle size of the particles was measured to be 0.6 μm.

(Film production)
A biaxially stretched film film was obtained in the same manner as in Example 1 except that the calcium carbonate particles 1 obtained above were used in the amounts shown in Table 1 instead of the barium sulfate particles 1. The evaluation results are shown in Table 1.

[Example 4]
A biaxially stretched film was prepared and evaluated in the same manner as in Example 3 except that the amount of calcium carbonate particles 1 added was adjusted as shown in Table 1.

[Example 5]
Among poly-4-methylpentene-1 (PMP) manufactured by Mitsui Chemicals, a melt flow rate (MFR) = 230 g / 10 min is prepared, and the ratio shown in Table 1 is used instead of barium sulfate particles 1 A biaxially stretched film was prepared in the same manner as in Example 1 except for the above. The evaluation results are shown in Table 1.

[Example 6]
A polypropylene (PP) with MFR = 15 g / 10 min was prepared, added in place of the barium sulfate particles 1 so as to have the ratio shown in Table 1, and other than that, a biaxially stretched film was prepared in the same manner as in Example 1. . The evaluation results are shown in Table 1.

[Comparative Examples 1, 3, 4]
A biaxially stretched film was prepared in the same manner as in Example 1 except that the embodiment was as shown in Table 1. Each evaluation result is shown in Table 1.

[Comparative Example 2]
(Production of barium sulfate particles 3)
A barium powder pulverized was adjusted by wind classification so that the average particle size became 7 μm, and barium sulfate particles 3 were obtained. The average particle diameter was confirmed with an electron microscope.

(Film production)
A biaxially stretched film was prepared in the same manner as in Example 1 except that barium sulfate particles 3 were used in place of barium sulfate particles 1 as the void nucleating agent for layer A, and the composition was as shown in Table 1. went.

[Reference Example 1]
Measurement was carried out without installing a film on the light source side of the polycarbonate plate. The evaluation results are shown in Table 1.

  The heat shield film of the present invention can be suitably used as a heat shield film for protecting an electronic circuit, and its industrial applicability is high.

11 Halogen Lamp 12 Evaluation Sample 13 Polycarbonate Plate 14 Black Drawing Paper 15 Thermography 21 Straight Line 22 in the Center Left and Right Straight Lines 23 Width Direction Edge 24 Width Direction 25 Thickness Direction

Claims (3)

  A film comprising a resin composition and having a resin layer containing voids, wherein the resin layer has a thickness of 50 μm or more, and the number of voids per 100 μm thickness in the thickness direction is 50 to 500/100 μm. A thermal barrier film for protecting electronic circuits.   2. The thermal barrier film for protecting an electronic circuit according to claim 1, wherein the number of voids having a height of 0.1 to 5.0 μm is 50 to 500/100 μm per 100 μm thickness in the thickness direction. .   The heat shielding film for protecting an electronic circuit according to claim 1 or 2, which is used for protecting an electronic circuit for communication.