JP4836414B2 - Light reflector and surface light source device using the same - Google Patents

Description

  INDUSTRIAL APPLICABILITY The present invention is useful as a light reflecting member used in a light reflector, a reflector and various lighting fixtures used in a surface light source device, and the surface is hardly damaged even if various types of processing are performed. The present invention relates to an excellent light reflector and a surface light source device using the light reflector.

  Backlight type liquid crystal displays with built-in light sources are widely used. A typical structure of the direct backlight among the backlight type built-in light sources is as shown in FIG. 1, and includes a housing 11 serving as a structure and a light reflector, a diffuser plate 14, a cold cathode lamp 15, and the like. It consists of a light source. A typical configuration of the sidelight type backlight is as shown in FIG. 2, such as a light guide plate obtained by performing dot printing 12 on a transparent acrylic plate 13, a light reflector 11, a diffusion plate 14, a cold cathode lamp 15, and the like. The light source. In either case, the light from the light source is reflected by the light reflector, and uniform light is formed by the diffusion plate. In recent years, improvements have been made to increase the output of illumination light sources and increase the number of light source lamps. A plurality of light sources may be installed as shown in FIG. 1 and FIG.

  Conventionally, a white polyester film has often been used as a light reflector for this application (for example, Patent Document 1). However, in the case of a light reflector using a white polyester film, a change in the color tone (yellowing) of the light reflector may become a problem due to a recent increase in the amount of light and an increase in the ambient temperature due to heat from the lamp. There was a demand for materials with less discoloration.

Therefore, in recent years, a light reflector using a white polyolefin film has been proposed (for example, Patent Documents 2 and 3). The light reflector using the white polyolefin film has less change in color tone than the light reflector using the white polyester film (for example, Patent Documents 4 and 5), but is bonded to a metal or other plate material. However, when various molding processes are performed, there has been a problem that floating or dropping occurs due to destruction of the bonded portion. In addition, it has been clarified that even when a protective tape for protecting the surface is used in some cases, the surface of the white polyolefin film is peeled off due to the adhesive force.
Further, as the size of display objects increases, the demand for improvement in luminance increases, and conventional white polyester films and white polyolefin films are not sufficient, and there is a demand for light reflectors with higher luminance.

JP-A-4-239540 JP-A-6-298957 JP 2002-31704 A JP-A-8-262208 WO 03/014778

  The present invention provides a light reflector that has high brightness and is excellent in workability because it does not easily float, drop off, or peel off from the bonded plate material even if it is bonded to various plate materials. The purpose is to do.

  As a result of intensive studies, the inventors of the present invention have a laminated film containing a thermoplastic resin and a filler excellent in reflection characteristics as a light reflector, and have a surface strength of 250 g or more and a scattering coefficient S of 0.5 or more. The present invention has been completed by imparting specific characteristics such as.

That is, this invention contains a thermoplastic resin and a filler, is stretched in at least one axial direction, and has a base layer (A) having an area stretch ratio of 1.3 to 80 times and a layer containing a thermoplastic resin (B The light reflection is characterized in that the total light reflectance is 95% or more, the surface strength is 250 g or more, and the scattering coefficient S represented by the formula (1) is 0.5 or more. Is the body.
100 x R1
Scattering coefficient S = ――――――――――――――――― Equation (1)
_{(100-R1) × T A} × P
(In the above formula, R1 is the reflectance at a wavelength of 550 nm, T _A is the thickness [unit μm] of the base material layer (A), and P is the porosity [unit%] represented by formula (2). )
ρ ₀ −ρ
Porosity P = ―――――――― × 100 Formula (2)
ρ ₀
(In the above formula, ρ ₀ is the true density of the laminated film, and ρ is the density of the laminated film)

The laminated film of the present invention preferably has a luminance of 1380 cd / m ² or more, a reflectance R2 at a wavelength of 450 nm of 98% or more, and a diffuse reflectance of 93% or more, and contains a thermoplastic resin. the thickness of the layer (B) is Ru der more than 2μm. The filler concentration of the base material layer (A) is 5 to 75% by weight, and the filler is a surface-treated inorganic filler having an average particle size of 0.05 to 1.5 μm. The porosity of the laminated film is preferably 15 to 60%, and the layer (B) containing the thermoplastic resin is preferably stretched at least in the uniaxial direction. The thermoplastic resin is a polyolefin resin. Is preferred. Furthermore, the present invention includes a surface light source device using the light reflector.

  The light reflector of the present invention has high brightness and excellent workability. Even if the light reflector of the present invention is bonded to various plate materials and molded, it is difficult to generate floating, dropping off, peeling, etc. from the bonded plate materials. Moreover, the surface light source device manufactured using the light reflector of the present invention has high brightness and is extremely useful.

BEST MODE FOR CARRYING OUT THE INVENTION

  Below, the structure and effect of the light reflector of this invention are demonstrated in detail. In the present invention, “to” means a range including numerical values described before and after that as a minimum value and a maximum value, respectively.

[Base material layer (A)]
Thermoplastic resin The type of the thermoplastic resin used for the base material layer (A) of the present invention is not particularly limited. Examples of the thermoplastic resin (A) used for the base film include ethylene resins such as high density polyethylene, medium density polyethylene, and low density polyethylene, propylene resins, polymethyl-1-pentene, and ethylene-cycloolefin copolymers. Polyolefin resins, nylon-6, nylon-6,6, nylon-6,10, nylon-6,12 and other polyamide resins, polyethylene terephthalate and copolymers thereof, polyethylene naphthalate, aliphatic polyester, etc. Thermoplastic resins such as plastic polyester resin, polycarbonate, atactic polystyrene, syndiotactic polystyrene, polyphenylene sulfide and the like can be mentioned. These may be used in combination of two or more.
Among these, from the viewpoint of chemical resistance and production cost, it is preferable to use a polyolefin resin, and it is more preferable to use a propylene resin.

  Examples of the propylene-based resin include a propylene homopolymer, and a copolymer of propylene as a main component and an α-olefin such as ethylene, 1-butene, 1-hexene, 1-heptene, and 4-methyl-1-pentene. Can be used. The stereoregularity is not particularly limited, and isotactic or syndiotactic and those showing various degrees of stereoregularity can be used. Further, the copolymer may be a binary system, a ternary system, or a quaternary system, and may be a random copolymer or a block copolymer.

  Such a thermoplastic resin is preferably used in the base layer (A) at 25 to 95% by weight, and more preferably 30 to 90% by weight. If the content of the thermoplastic resin in the base material layer (A) is 25% by weight or more, there is a tendency that the surface is hardly scratched at the time of stretch molding of the laminated film described later. There is a tendency that the number of holes is easily obtained.

As the filler used base layer of filler present invention (A) with the thermoplastic resin, using a variety of inorganic filler over surface treated.
Examples of the inorganic filler include heavy calcium carbonate, precipitated calcium carbonate, calcined clay, talc, titanium oxide, barium sulfate, aluminum sulfate, silica, zinc oxide, magnesium oxide, diatomaceous earth, and the like. In this invention, the surface treatment goods by the various surface treating agent of the said inorganic filler are used. Good Mashiino is heavy calcium carbonate, surface treated product with various surface treatment agents of precipitated calcium carbonate. As the surface treatment agent, for example, resin acid, fatty acid, organic acid, sulfate ester type anionic surfactant, sulfonic acid type anionic surfactant, petroleum resin acid, salts thereof such as sodium, potassium, ammonium, or These fatty acid esters, resin acid esters, waxes, paraffins and the like are preferable, and nonionic surfactants, diene polymers, titanate coupling agents, silane coupling agents, and phosphoric acid coupling agents are also preferable. Examples of sulfate-type anionic surfactants include long-chain alcohol sulfates, polyoxyethylene alkyl ether sulfates, sulfated oils, and their salts such as sodium and potassium, and sulfonate-type anionic surfactants. Examples of the agent include alkylbenzene sulfonic acid, alkyl naphthalene sulfonic acid, paraffin sulfonic acid, α-olefin sulfonic acid, alkyl sulfosuccinic acid and the like, and salts thereof such as sodium and potassium. Examples of fatty acids include caproic acid, caprylic acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, hebenic acid, oleic acid, linoleic acid, linolenic acid, and eleostearic acid. Examples of the organic acid include maleic acid and sorbic acid. Examples of the diene polymer include polybutadiene and isoprene. Examples of the nonionic surfactant include a polyethylene glycol ester type surfactant. Agents and the like. These surface treatment agents can be used alone or in combination of two or more. Examples of the surface treatment method of the inorganic filler using these surface treatment agents include, for example, JP-A-5-43815, JP-A-5-139728, JP-A-7-300568, and JP-A-10-176079. JP-A-11-256144, JP-A-11-349846, JP-A-2001-158863, JP-A-2002-220547, JP-A-2002-363443, etc. can be used.

The average particle diameter of the inorganic filler is , for example, the observation of the primary particle diameter by a microtrack method or a scanning electron microscope (in the present invention, the average value of 100 particles is an average particle diameter), conversion from a specific surface area (the present invention) Then, the specific surface area was measured using a powder specific surface area measuring device SS-100 manufactured by Shimadzu Corporation.
In order to adjust the pore size generated by stretch molding of the laminated film described later, the average particle size of the inorganic filler is in the range of 0.05 to 1.5 μm , more preferably 0 . The thing of the range of 1-1 micrometer is used. If a filler having an average particle size of 1.5 μm or less is used, the pores tend to become more uniform. In addition, if a filler having an average particle size of 0.05 μm or more is used, predetermined pores tend to be obtained more easily.

For adjusting holes of generating the stretching of the laminated film to be described later, the compounding amount of the filler into the oriented film in the 5-75 wt%, the good Mashiku the range of 10 to 70 wt%. If the blending amount of the filler is 5% by weight or more, a sufficient number of pores tends to be obtained. Moreover, if the blending amount of the filler is 75% by weight or less, scratches tend to be less likely to occur on the surface.

In the case where the main resin constituting the other component base material layer (A) is a propylene resin, in order to improve stretchability, a resin having a lower melting point than propylene resins such as polyethylene and ethylene vinyl acetate is used in an amount of 3 to 25 wt. % May be blended.

  The base material layer (A) used in the present invention may have a single layer structure or a multilayer structure. 30-500 micrometers is preferable, as for the thickness of a base material layer (A), 40-400 micrometers is more preferable, and 50-300 micrometers is more preferable.

[Layer containing thermoplastic resin (B)]
The layer (B) containing the thermoplastic resin may be formed on one side or both sides of the base material layer (A).
As a method for forming the layer (B), before the base material layer (A) is stretch-molded, a multilayer T die or I die is used to co-extrus the molten raw material of the layer (B), and the resulting laminate is stretched. In the case where the base material layer (A) is biaxially stretched by forming, the molten raw material of the layer (B) is extruded and bonded after the uniaxial stretching is completed, and this laminate is uniaxially stretched. Examples thereof include a method of molding and providing, and a method of providing the raw material resin of the layer (B) by extruding and bonding directly or through an easy-adhesion layer after the base material layer (A) is stretch-molded.

The thermoplastic resin similar to what is used for a base material layer (A) can be used for the said layer (B). Moreover, the said filler may be contained and the compounding quantity of a filler can be used in the range below 5 weight%.
When the layer (B) does not contain a filler, the one containing 40 to 60% by weight of propylene-based resin and 60 to 40% by weight of high-density polyethylene controls the glossiness of the laminated film to 70 to 86%, and increases the brightness. It is preferable because an excellent light reflector can be obtained.

The thickness of the layer (B) is 2 μm or more , preferably 2 to 80 μm , and more preferably 2.5 to 60 μm. When the thickness is 2 μm or more, a surface strength of 250 g or more can be easily obtained, and desired processing characteristics can be easily obtained.

[Laminated film]
Additives If necessary, the laminated film of the present invention may contain a fluorescent whitening agent, a stabilizer, a light stabilizer, a dispersant, a lubricant and the like. Stabilizers such as sterically hindered phenols, phosphorus and amines are used as stabilizers in an amount of 0.001 to 1% by weight. Light stabilizers such as sterically hindered amines, benzotriazoles and benzophenones are used as stabilizers. 0.001 to 1% by weight, as a dispersant for inorganic filler, 0.01% of silane coupling agent, higher fatty acids such as oleic acid and stearic acid, metal soap, polyacrylic acid, polymethacrylic acid or salts thereof, etc. You may mix | blend -4weight%.

As a method for forming the molded laminated film, a general uniaxial stretching or biaxial stretching method can be used. As a specific example, a single layer or multi-layer T die or I die connected to a screw type extruder is used to extrude the molten resin into a sheet shape, and then uniaxially by longitudinal stretching utilizing the peripheral speed difference of the roll group. Examples thereof include a stretching method, a biaxial stretching method in which transverse stretching using a tenter oven is subsequently combined, and simultaneous biaxial stretching by a combination of a tenter oven and a linear motor.

The stretching temperature is 2 to 60 ° C. lower than the melting point of the thermoplastic resin used and 2 to 60 ° C. higher than the glass transition point. When the resin is a propylene homopolymer (melting point 155 to 167 ° C.), 95 to 165 is used. In the case of ° C and polyethylene terephthalate (glass transition point: about 70 ° C), 100 to 130 ° C is preferable. The stretching speed is preferably 20 to 350 m / min.
The obtained laminated film can be subjected to heat treatment (annealing treatment) as necessary to promote crystallization and reduce the thermal shrinkage rate of the laminated film.

  In order to adjust the size of the pores generated in the laminated film, the area stretch ratio of the base material layer (A) is set in the range of 1.3 to 80 times, preferably in the range of 7 to 70 times, more preferably. 22 times to 65 times, most preferably 25 times to 60 times. If the area stretch ratio is in the range of 1.3 to 80 times, fine pores are easily obtained, and a decrease in reflectance is easily suppressed.

In order to adjust the amount per unit volume of pores generated in the laminated film of the present invention, the porosity is preferably 15 to 60%, more preferably 20 to 55%. In this specification, the “porosity” means a value calculated according to the above formula (2). In the equation (2), ρ ₀ represents a true density, and ρ represents a density (JIS-P8118). Unless the material before stretching contains a large amount of air, the true density is approximately equal to the density before stretching.

The density of the laminated film used in the present invention is generally in the range of 0.5 to 1.2 g / cm ³ , and as the number of holes increases, the density decreases and the porosity increases. The higher the porosity, the better the surface reflection characteristics.

[Light reflector]
The light reflector of the present invention is characterized by having the above laminated film. The light reflector of the present invention may be composed only of the above laminated film, or may be a material obtained by further adding an appropriate material to the above laminated film.

  For example, the light reflector of the present invention may have a structure in which another layer is laminated on a laminate comprising a base material layer (A) and a layer (B) containing a thermoplastic resin. Specifically, it may have a structure in which a layer (B) containing a thermoplastic resin is laminated on both surfaces of the base material layer (A), or a layer containing a base material layer (A) and a thermoplastic resin ( You may have the structure which laminated | stacked the protective layer (C) on the one surface or both surfaces of the laminated body which consists of B). That is, (A) / (B), (B) / (A) / (B), (C) / (A) / (B), (A) / (B) / (C), (C) / (A) / (B) / (C), (B) / (A) / (B) / (C), (C) / (B) / (A) / (B) / (C), etc. The light reflector which has can be illustrated.

  The total light reflectivity R of the light reflector of the present invention means the average value of the reflectivities of each wavelength measured in the wavelength range of 400 to 700 nm according to the method described in JIS-Z8722 condition d. The total light reflectance R of the light reflector of the present invention is 95% or more, preferably 96% or more, and more preferably 97% to 100%. The reflectance R1 at a wavelength of 550 nm is preferably 97% or more, more preferably 98.5 or more, and the reflectance R2 at a wavelength of 450 nm is preferably 98% or more, more preferably 98.5% or more. Is particularly desirable as the light reflector of the present invention.

In the light reflector of the present invention, the scattering coefficient S defined by the above formula (1) is 0.5 or more, preferably 0.6 or more, more preferably 0.8 or more. The scattering coefficient S means the degree of light scattering per unit volume of pores, and is proportional to R1 and inversely proportional to the thickness T _A and the porosity P of the base material layer (A). According to the present invention, by forming many flat and fine pores in the base material layer (A) with a finer and uniform size, the light reflection can be performed without making the base material layer (A) thicker than necessary. It became possible to obtain a desired luminance as a body.

  The diffuse reflectance Rd was measured according to the method described in JIS-Z8722 condition d, using an optical trap, cutting the regular reflection component, and measuring the reflectance at a wavelength of 400 to 700 nm. The average value was defined as the diffuse reflectance Rd. It is preferably 93% or more, and more preferably 95 to 100%. A diffuse reflectance of 93% or more is preferable because uneven luminance is less likely to occur when a surface light source device such as a surface light source device is produced using the light reflector of the present invention.

The luminance of the light reflector can be measured by the method described later. Brightness of the light reflector of the present invention is preferably 1380cd / m ² or more, more preferably 1400cd / m ² or more, more preferably ^{1420cd / m 2 ~3000cd / m 2} , particularly preferably 1440cd / m ² ~2000cd / m ² .

  The surface strength of the light reflector of the present invention is 250 g or more, preferably 270 to 1000 g. The surface strength as used in this specification means a peeling load when an adhesive tape having a width of 18 mm is applied to the measurement surface of the light reflector and peeled at a speed of 300 mm / min, as shown in the measurement method described later. If the surface strength is 250 g or more, it is possible to avoid problems such as floating and peeling when the light reflector of the present invention is bonded to a plate material and subjected to various molding processes.

  Hereinafter, the present invention will be described more specifically with reference to Examples, Comparative Examples and Test Examples. The materials, amounts used, ratios, operations, and the like shown below can be changed in a timely manner without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. The materials used in this example are shown in Table 1.

Example 1
A composition (A) obtained by mixing the materials shown in Table 1 with the formulation shown in Table 2 was melt-kneaded at 250 ° C. using an extruder. Thereafter, the sheet was extruded and cooled to about 60 ° C. with a cooling roll to obtain a sheet. This sheet was reheated to 145 ° C. and then stretched in the longitudinal direction by utilizing the peripheral speed difference of a number of roll groups.
A composition (B) obtained by mixing the materials shown in Table 1 with the formulation shown in Table 2 is melt-kneaded with two extruders, and (B) is placed on both sides of the stretched sheet obtained above. The layers were extruded and laminated in a die to obtain a laminate (B) / (A) / (B). The laminate was then reheated to 160 ° C. and stretched in the transverse direction with a tenter.
Then, after annealing at 160 ° C., it was cooled to 60 ° C., and the ears were slit to obtain a laminated film having a three-layer structure. The vertical and horizontal draw ratios and the thickness of each layer are as shown in Table 2. This laminated film was used as a light reflector.

(Example 2)
A light reflector was obtained in the same manner as in Example 1 using compositions (A) and (B) obtained by mixing the materials shown in Table 1 with the composition shown in Table 2.

(Example 3)
A light reflector was obtained in the same manner as in Example 1 using compositions (A) and (B) obtained by mixing the materials shown in Table 1 with the composition shown in Table 2.

(Comparative Example 1)
The laminate obtained in Example 5 of JP 2002-31704 A was used as a light reflector.

(Comparative Example 2)
The laminate obtained in Example 6 of JP 2002-31704 A was used as a light reflector.

(Comparative Example 3)
The three-layer film obtained in Example 3 of WO 03/014778 was used as a light reflector.

(Test method)
The following tests were conducted using the light reflectors of Examples 1 to 3 and Comparative Examples 1 to 3.

Total light reflectance R:
The average value of the reflectance of each wavelength measured in the wavelength range of 400 to 700 nm according to the method described in JIS-Z8722 condition d was defined as the total light reflectance R.

Reflectivity R1, R2:
The reflectance at a wavelength of 550 nm measured according to the method described in JIS-Z8722 Condition d was R1, and the reflectance at 450 nm was R2.

Diffuse reflectance Rd:
According to the method described in JIS-Z8722 Condition d, a specular reflection component was cut using an optical trap, and the reflectance measurement at a wavelength of 400 to 700 nm was performed. The average value was defined as the diffuse reflectance Rd.

Luminance:
Each light reflector is set at the position 11 of the 14-inch size surface light source device illustrated in FIG. 2, and an Harrison (manufactured) inverter unit is connected to the cold cathode lamp 15, and the cold cathode lamp has 12V, 6 mA. A tube current was applied to light and irradiate, and the following evaluation was performed after 3 hours.
The luminance is a luminance meter (trade name: BM-7) manufactured by Topcon Corporation, and the distance between the luminance measuring unit and the surface light source device is 50 cm with respect to the normal direction of the surface light source device. Was measured and the average value was obtained.

Surface strength:
The surface strength was measured by the following procedure. Adhesive tape with a width of 18 mm (made by Nichiban, trade name: cello tape (registered trademark)) is pasted to a measuring surface of the light reflector with a length of 100 mm or more, and the last 10 mm or more is not pasted. left. The sample was cut to a width of 20 mm. Using a load cell for a load of 5 kg with a tensile tester (made by Orientec Co., Ltd., trade name: RTM-250), set the chuck interval to 1 cm, and do not attach the part of the adhesive tape left unattached and the adhesive tape Each light reflector was sandwiched between upper and lower chucks. Pulling was performed at a speed of 300 mm / min, and the load on the stable portion of the chart was read. The surface strength was obtained by measuring three times and calculating the average value.

Processability:
The light reflectors obtained in Examples and Comparative Examples were bonded to a stainless steel plate (SUS # 5052, thickness 0.6 mm) with an adhesive (manufactured by Toyo Morton, trade name: TM590) and a curing agent (manufactured by Toyo Morton, The product was dry-laminated using a product name: CAT56) to prepare a sample. A protective film (manufactured by Sekisui Chemical Co., Ltd., product number: # 6312B) is bonded to the light reflector side of this sample, and an angle of 90 ° is opposite to each other with a press so that the light reflector side becomes a mountain and a valley. The two places were bent and the protective film was peeled off, and the following evaluation was performed.
○ There is no lifting or peeling from the stainless steel plate, and no peeling of the reflector surface.
X Lifting or peeling from the stainless steel plate, peeling of the reflector surface is observed.

  These measurement results are shown in Table 2.

  The light reflector of the present invention has high brightness and excellent workability. Even if the light reflector of the present invention is bonded to various plate materials and molded, it is difficult to generate floating, dropping off, peeling, etc. from the bonded plate materials. Moreover, the surface light source device manufactured using the light reflector of the present invention has high brightness and is extremely useful. Therefore, the present invention can be used for industrial production of light reflectors and surface light source devices, and is industrially useful.

It is sectional drawing which shows the structure of a direct type | mold backlight. It is sectional drawing which shows the structure of a sidelight type backlight.

Explanation of symbols

11 Light reflector (housing)
12 White dot printing for reflection 13 Acrylic plate (light guide plate)
14 Diffuser 15 Cold Cathode Lamp

Claims (7)

A laminated film comprising a base material layer (A) containing a thermoplastic resin and a filler, stretched in at least one axial direction and having an area stretch ratio of 1.3 to 80 times, and a layer (B) containing a thermoplastic resin A light reflector having
The filler concentration of the base material layer (A) is 5 to 75% by weight, and the filler is a surface-treated inorganic filler having an average particle size of 0.05 to 1.5 μm,
The thickness of the layer (B) containing the thermoplastic resin is 2 μm or more,
A light reflector having a total light reflectance of 95% or more, a surface strength of 250 g or more, and a scattering coefficient S represented by the formula (1) of 0.5 or more.
100 x R1
Scattering coefficient S = ――――――――――――――――― Equation (1)
_{(100-R1) × T A} × P
(In the above formula, R1 is the reflectance at a wavelength of 550 nm, T _A is the thickness [unit μm] of the base material layer (A), and P is the porosity [unit%] represented by formula (2). )
ρ ₀ −ρ
Porosity P = ―――――――― × 100 Formula (2)
ρ ₀
(In the above formula, ρ ₀ is the true density of the laminated film, and ρ is the density of the laminated film) The light reflector according to claim 1, wherein the luminance is 1380 cd / m ² or more.   The light reflector according to claim 1 or 2, wherein the reflectance R2 at a wavelength of 450 nm is 98% or more and the diffuse reflectance Rd is 93% or more. The light reflector according to any one of claims 1 to 3 , wherein a porosity P of the laminated film is 15 to 60%. The light reflector according to any one of claims 1 to 4 , wherein the layer (B) containing the thermoplastic resin is stretched in at least one axial direction. Light reflector according to any one of claims 1 to 5, a thermoplastic resin is characterized in that it is a polyolefin resin. A surface light source device using the light reflector according to any one of claims 1-6.

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