Patent Description:
In the related art, silicone resin parts have been used in vehicle lamps. In particular, in recent years, a lens made of a silicone resin has been adopted from the viewpoint of complicated shape and heat resistance (see <CIT>).

The silicone resin is known to release a cyclic low molecular weight siloxane (hereinafter simply referred to as a low molecular weight siloxane) as outgas. The cyclic low molecular weight siloxane is a residue of a silicone resin raw material that remains unreacted during silicone resin molding. In particular, reducing the residual amount of D3 to D10 low molecular weight siloxanes is an index of the quality standard for the silicone resin. In the vehicle lamp, a silicone resin with a reduced amount of low molecular weight siloxanes (low siloxane control grade) in which the content of the D3 to D10 low molecular weight siloxanes is reduced to <NUM> ppm or less is also generally used. It is also known to use a silicone resin with a reduced amount of low molecular weight siloxanes (low siloxane control grade) in which the content of the D4 to D10 low molecular weight siloxanes is reduced to <NUM> ppm or less (see <CIT>).

On the other hand, a configuration in which an anti-fogging film is provided on an inner surface of a front cover is often adopted in the vehicle lamp (see <CIT> or <CIT>). However, in recent years, in the vehicle lamp provided with an anti-fogging film, problems caused by deterioration in anti-fogging performance such as water dripping marks on the front cover have been studied.

Therefore, as a result of studies, the present inventors have found that in the vehicle lamp in the related art, the anti-fogging performance may deteriorate even though the silicone resin part with a reduced amount of low molecular weight siloxane is used.

The present invention has been made in view of such circumstances, and an object thereof to provide to prevent deterioration in anti-fogging performance in a vehicle lamp including a silicone resin part.

In order to achieve the above object, a vehicle lamp according to an aspect of the present invention includes: a lamp body that has an opening in a direction of light radiation; a front cover that covers the opening to define a housing and includes, on an inner surface, an anti-fogging film mainly composed of a synthetic resin; a light source that is disposed in the housing; and a silicone resin part that is disposed in the housing. A content of D3 to D20 cyclic low molecular weight siloxanes in the silicone resin part is <NUM> ppm to <NUM> ppm in terms of mass.

In a vehicle lamp in the related art, a silicone resin part having a controlled content of D3 to D10 is used, but the content of D11 to D20 is not taken into consideration. According to the above configuration, when the total content of the D3 to D20 low molecular weight siloxanes in the silicone resin part is reduced to be less than <NUM> ppm, it is possible to reduce the amount of the low molecular weight siloxane released from the silicone resin part in the housing, which is in a high temperature in a lighting state. As a result, the influence of the low molecular weight siloxane on the anti-fogging film formed on the inner surface of the front cover can be reduced, and deterioration in anti-fogging performance can be prevented.

In the above aspect, it is preferable that a lens that is disposed in the housing is further included and at least one of the silicone resin part is the lens.

In the above aspect, it is preferable that a content of D11 to D20 cyclic low molecular weight siloxanes in the silicone resin part is <NUM> ppm to <NUM> ppm in terms of mass.

In the above aspect, it is preferable that the content of the D3 to D20 cyclic low molecular weight siloxanes is <NUM> ppm to <NUM> ppm in terms of mass.

In the above aspect, it is preferable that the content of the D11 to D20 cyclic low molecular weight siloxanes is <NUM> ppm to <NUM> ppm in terms of mass.

It is preferable that the anti-fogging film contains an anti-fogging coating material containing any of anionic, cationic and nonionic surfactants.

In the present description, the "content of the low molecular weight siloxane" (unit: ppm) in the silicone resin part refers to a total content (in terms of mass) of specific cyclic dimethyl siloxanes (molecular formula SiO(CH3)<NUM>) per unit mass of the silicone resin part, and means a total content (in terms of mass) of D3 to D20 low molecular weight siloxanes in the case of the content of D3 (trimer) to D20 (20mer) low molecular weight siloxanes.

According to the vehicle lamp in the above aspect, it is possible to provide to prevent deterioration in anti-fogging performance in a vehicle lamp including a silicone resin part.

Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

In the following description, unless otherwise specified, a term indicating a direction such as up, down, left, or right with respect to a vehicle lamp (hereinafter, also simply referred to as "lamp") means a direction when the lamp is viewed from the front with the lamp attached to a vehicle. That is, the "front" of the lamp means the front of the vehicle, the left of the lamp means the right of the vehicle, and the right of the lamp means the left of the vehicle. In the drawings, arrows U-D indicate an up-down direction when the lamp is viewed from the front, arrows F-B indicate the same front-rear direction, and arrows L-R indicate the same left-right direction.

<FIG> is a front view schematically showing a schematic structure of a lamp <NUM> according to an embodiment of the present invention. <FIG> is a cross-sectional view of the lamp <NUM> along a line IIA-IIA in <FIG>. The lamp <NUM> is a left or right head light unit of a vehicle head light device including a pair of head light units disposed on the left and right in the front of the vehicle. The pair of head light units have substantially the same configuration.

The lamp <NUM> roughly includes a lamp body <NUM>, a front cover <NUM>, a high beam unit HU, a low beam unit LU, and a bracket unit <NUM>.

The lamp body <NUM> is made of a synthetic resin such as polypropylene, acrylonitrile, styrene, or acrylate (ASA), and has a box-like shape having a forward opening in a direction of light radiation. The front cover <NUM> defines a housing <NUM> by closing the opening of the lamp body <NUM>.

The front cover <NUM> is made of, for example, a synthetic resin having excellent translucency and impact resistance. As the material, for example, polycarbonate (PC) or polymethyl methacrylate (PMMA) can be adopted. The front cover <NUM> may be transparent and may have a lens cut (not shown) formed in a part of an inner surface thereof.

An anti-fogging film <NUM> is formed on the inner surface of the front cover <NUM>. The anti-fogging film <NUM> may be formed by using, for example, a spray gun to spray a translucent anti-fogging coating material P from a nozzle of the spray gun onto the inner surface of the front cover <NUM> and performing heating with warm air or the like to cure the film while moving the nozzle along the inner surface.

As the anti-fogging coating material P, for example, a known anti-fogging coating material containing any of anionic, cationic and nonionic surfactants, a resin such as an acrylic resin, and a curing agent (catalyst) can be adopted. For example, a curable anti-fogging coating material described in <CIT> or the like may be adopted.

In the surfactant, hydrophobic groups are oriented toward the inner surface of the front cover <NUM>, and hydrophilic groups face outward. Whereby, the anti-fogging performance of the anti-fogging coating material P containing the surfactant is exhibited such that interfacial tension between water and the front cover <NUM> at a contact point of the adhered water droplet is reduced and a contact angle at the contact point is reduced. A cyclic low molecular weight siloxane has low polarity, and when it adheres to the anti-fogging film, an effect of lowering the interfacial tension of the anti-fogging film <NUM> is reduced.

The high beam unit HU and the low beam unit LU are disposed in the housing <NUM>. The high beam unit HU and the low beam unit LU are held by the bracket unit <NUM>.

The high beam unit HU is a variable light distribution head lamp (ADB: adaptive driving beam) configured to form a predetermined shape or light distribution with light emitted forward, and can form a variable light distribution by adapting not only to a high beam light distribution but also to a driving situation of the vehicle and a surrounding situation.

The high beam unit HU includes a light source <NUM>, a scanning mechanism <NUM>, a condensing lens <NUM> that condenses light emitted from the light source <NUM> and causes the light to be incident on the scanning mechanism <NUM>, a control unit <NUM> that controls the scanning mechanism <NUM> and the light source <NUM>, a projection lens <NUM>, and a lens holder <NUM>. These components are supported by the bracket unit <NUM> by appropriate means.

The light source <NUM> is a semiconductor light emitting element such as a light emitting diode (LED) or an electro luminescence (EL). The light source <NUM> is not limited to this, and may be a laser diode (LD) element.

As shown enlarged in <FIG>, the scanning mechanism <NUM> is a rotating reflector having a reflection surface <NUM> in which three blades 14a having the same shape are provided around a cylindrical rotating portion 14b, which is configured to rotate so as to reflect the light emitted from the light source <NUM> to form a desired light distribution pattern. A rotation axis r is oblique to an optical axis M of the light source, and is provided on a plane including the optical axis M and the light source <NUM>.

The blade 14a has a shape enabling formation of a secondary light source caused by the reflection of the light source <NUM> near a rear focal point of the projection lens <NUM>. Further, the blade 14a has a twisted shape such that an angle formed by an optical axis Ax and the reflection surface <NUM> changes toward a circumferential direction centered on the rotation axis r. The scanning mechanism <NUM> scans the light from the light source <NUM> in the left-right direction by reflecting the light reflected by the reflection surface <NUM> to change the direction while rotating around the rotation axis r.

The projection lens <NUM> is made of, for example, a translucent resin such as polycarbonate or PMMA, and radiates the light incident from the blade 14a forward.

As a result, the light from the light source <NUM> is condensed by the condensing lens <NUM> and incident on the rotating reflector, i.e., the scanning mechanism <NUM>. The light incident on the rotating reflector is scanned left and right by the reflection surface <NUM>. The projection lens <NUM> receives the light from the rotating reflector and radiates the light forward. In this way, in the high beam unit HU, the light incident at positions on the projection lens <NUM> overlaps to form a predetermined light distribution pattern.

The low beam unit LU includes a projector-type optical unit Lo1 including a light source which is a light emitting element, a reflector, and a projection lens. Since the optical unit Lo1 has a configuration same or similarly as a low beam unit described in, for example, <CIT>, detailed description thereof will be omitted.

The low beam unit LU includes the optical unit Lo1 and an optical unit Lo2 having a configuration same or similarly as the optical unit Lo1, and the two optical units Lo1 and Lo2 form a low beam light distribution in front of the vehicle.

The bracket unit <NUM> includes a base plate 6a having a shape that conforms to a front shape of the lamp <NUM>, and three aiming screws E provided at three positions at upper and lower sides. Optical axes of the high beam unit HU and the low beam unit LU are adjusted in a horizontal direction and a vertical direction by rotating the aiming screws E.

Reference numeral <NUM> in the housing <NUM> denotes an extension, which surrounds the low beam unit LU and the high beam unit HU so as to cover peripheries thereof.

Here, the condensing lens <NUM> which is a silicone resin part in the lamp <NUM> according to the present embodiment will be described. The condensing lens <NUM> is produced by injection molding using a highly transparent silicone resin for optical parts as a base polymer and a catalyst such as an organic peroxide or a platinum compound as a cross-linking agent. A total content of D3 to D20 low molecular weight siloxanes in the condensing lens <NUM> is <NUM> ppm to <NUM> ppm. In addition, a total content of D11 to D20 low molecular weight siloxanes is preferably <NUM> ppm to <NUM> ppm. The content of the D3 to D20 low molecular weight siloxanes is preferably <NUM> ppm to <NUM> ppm. The content of the D11 to D20 low molecular weight siloxanes is more preferably <NUM> ppm to <NUM> ppm.

The content of the low molecular weight siloxane can be controlled, for example, as follows.

Hereinafter, in order to evaluate the anti-fogging performance of the lamp <NUM> according to the present embodiment, condensing lenses <NUM> having different contents of low molecular weight siloxane were prepared. Then, the concentration of the low molecular weight siloxane in the prepared condensing lens <NUM> was measured, and an anti-fogging performance test using an oil bath was performed. The anti-fogging performance test using an oil bath is a test in which a test piece of the silicone resin part is sealed in a glass beaker covered with a plate coated with an anti-fogging coating, and heated to a temperature corresponding to a lighting state of the lamp and thereby it is possible to observe the state corresponding to a case where the vehicle lamp is lit on.

In lamps in Examples <NUM> and <NUM> and Comparative Examples <NUM> and <NUM> shown in Table <NUM>, the condensing lenses <NUM>, i.e., the silicone resin parts, were prepared by injection molding using a silicone elastomer having the material grades shown in Table <NUM> using the same mold and performing a post-treatment under the conditions shown in Table <NUM>.

The measurement of the content of the low molecular weight siloxane in the prepared silicone resin part was performed as follows.

The anti-fogging performance test was carried out by the following method using the following apparatus. <FIG> is a schematic view showing an outline of an anti-fogging performance test apparatus <NUM>.

The above experimental results are summarized in Table <NUM>.

As seen from Table <NUM>, no influence on the anti-fogging performance is observed from Reference Example in which the silicone resin part is not used. In addition, in Examples <NUM> and <NUM> in which the concentration of the D3 to D20 low molecular weight siloxanes is <NUM> ppm or less, in the anti-fogging performance test, fog does not occur in any of them, or even when fog occurs in a part of them, the film immediately becomes a water film, and the anti-fogging performance does not deteriorate. On the other hand, in those in which the content of the D3 to D10 low molecular weight siloxanes is <NUM> ppm, which is the so-called low siloxane range, but the concentration of the D3 to D20 low molecular weight siloxanes exceeds <NUM> ppm, as in Comparative Example <NUM>, fog occurs and the anti-fogging performance deteriorates in the anti-fogging performance test.

Therefore, in the anti-fogging performance test, it can be seen that the failure is due to the low molecular weight siloxane released from the condensing lens <NUM>, i.e., the silicone resin part. In addition, it can be seen that in order to ensure the anti-fogging performance after lighting for a long time, it is preferable that the content of the D3 to D20 low molecular weight siloxanes is <NUM> ppm or less (the concentration of the D11 to D20 low molecular weight siloxanes is <NUM> ppm or less) in the silicone resin part, as in Examples <NUM> and <NUM>. In addition, it can be seen that, it is preferable that the content of the D3 to D20 low molecular weight siloxanes is <NUM> ppm or less (the concentration of the D11 to D20 low molecular weight siloxanes is <NUM> ppm or less), as in Example <NUM>.

The reason why it is preferable to control the silicone resin part by paying attention to the content of D3 to D20, particularly D11 to D20, low molecular weight siloxanes is considered as follows. The distribution of low molecular weight siloxanes released from silicone resin products varies depending on the heating temperature. At a heating temperature of <NUM>, a lot of D3 to D10, mainly D5, are released. The higher the heating temperature, the greater the amount of low molecular weight siloxane released, with D14 to D20 predominant at <NUM>. It is considered that the inside of the housing <NUM> of the vehicle lamp <NUM> is in a relatively high temperature, and in particular, the temperature may reach <NUM> to <NUM> around the light source, and the amount of D11 to D20 released is large. Therefore, when the content of the D3 to D20 low molecular weight siloxanes contained in the silicone resin part is controlled by paying attention to the content of the D11 to D20 siloxanes released, the total amount of the low molecular weight siloxane released can be indirectly controlled.

In the present embodiment, the content of the low molecular weight siloxane contained in the silicone resin part is controlled to prevent the deterioration in anti-fogging performance. It is the concentration of the low molecular weight siloxane in the air in the housing that is directly involved in the deterioration in anti-fogging performance of the anti-fogging film, but it is difficult to control this. On the other hand, in the present embodiment, the content of the low molecular weight siloxane is controlled, the total amount of low molecular weight siloxanes released into the housing can be indirectly controlled. Therefore, even when the number and size of the silicone resin part or the capacity of the housing changes, it is possible to accurately design the configuration of the silicone resin part that does not interfere with the anti-fogging performance.

In the present embodiment, the effect of lowering interfacial tension between the water droplet and the anti-fogging film can be reduced by reducing the content of the low molecular weight siloxane. Therefore, in particular, when an anti-fogging coating material containing a surfactant is used as the anti-fogging coating material, the deterioration in anti-fogging performance can be prevented.

In the above description, the condensing lens <NUM> has been described as an example of the silicone resin part, but the silicone resin part in the present invention is not limited to this. Needless to say, it includes various silicone resin parts used in vehicle lamps.

Although the preferred embodiments of the present invention have been described above, the above embodiments are merely examples of the present invention, and these embodiments can be combined based on knowledge of those skilled in the art, and such forms are also included in the scope of the present invention.

Claim 1:
A vehicle lamp comprising:
a lamp body (<NUM>) that has an opening in a direction of light radiation;
a front cover (<NUM>) that covers the opening to define a housing (<NUM>) and includes, on an inner surface, an anti-fogging film (<NUM>) mainly composed of a synthetic resin; and
a light source (<NUM>) that is disposed in the housing; and
characterized by further comprising:
a silicone resin part (<NUM>) that is disposed in the housing, wherein
a content of D3 to D20 cyclic low molecular weight siloxanes in the silicone resin part is <NUM> ppm to <NUM> ppm in terms of mass.