[0065] For example, in a case where at least one of a specific acid or a salt of the specific acid is included in a retardation layer, decomposition of the ester group is sup› pressed. 

[0066] In addition, components included in each of the layers easily migrate in a wet heat environment. As a result, usually, even in a case where at least one of a specific acid or a salt of the specific acid is included in an alignment layer disposed adjacent to the retardation layer, at least one of a specific acid or a salt of the specific acid included in the alignment layer easily migrates into the retardation layer in the wet heat environment, and thus, the retardation layer is in an acidic environment, whereby decomposition of an ester group derived from the liquid crystal compound included in the retardation layer is suppressed. 

[0067] Hereinafter, the optical film of the embodiment of the present invention will be described with reference to drawings. FIG. 1 shows a cross-sectional view showing a first embodiment of the optical film. Further, the drawings in the present invention are schematic views, and the thickness relationship, the positional relationship, and the like of each of the layers do not necessarily match actual ones, which is also applied to the following drawing. 

[0068] FIG. 1 is a schematic cross-sectional view showing the first embodiment of the optical film of the present invention. In FIG. 1, an optical film lOA includes an alignment layer 12 and a retardation layer 14 disposed adjacent to the alignment layer 12. 

[0069] Hereinafter, each of members and materials included in the optical film will be described in detail. 

[0070] First, the specific acid and a salt thereof included in the optical film will be described in detail. 

[0071] At least one of the specific acid or a salt of the specific acid is included in at least one of the alignment layer or the retardation layer. Specifically, at least one of a specific acid or a salt of the specific acid may be included in only one of the alignment layer and the retardation layer, or at least one of the specific acid or a salt of the specific acid may be included in both of the alignment layer and the retardation layer. One or both of the specific acid and a salt thereof may be included in one of the respective layers or may be included in each of the layers. 

[0072] Moreover, a presence or content of the specific acid and a salt thereof included in the alignment layer and the retardation layer can be measured by using time-of-flight secondary ion mass spectrometry (TOP-SIMS). Further, as described in detail in later paragraphs, the amounts of the specific acid and a salt thereof included in the alignment layer and the retardation layer can also be calculated from the amounts of the specific acid or a salt thereof, and an acid generator that generates the specific acid, which are used. 

[0073] In a case where at least one of the specific acid or a salt of the specific acid is included in the alignment layer, the total content of the specific acid and a salt thereof in the alignment layer is not particularly limited, but from the viewpoint that the wet heat resistance of the optical film is more excellent, the total content is preferably 0.10% to 5.00% by mole, and more preferably 0.20% to 2.50% by mole, with respect to the liquid crystal compound repre› sented by Formula (I) used for the formation of the retar› dation layer. Further, a specific amount of the total content of the specific acid and a salt thereof is preferably 0.25 to 12.3 nmol/cm 2 in the alignment layer. 

[0074] Furthermore, in a case where at least one of the specific acid or a salt of the specific acid is included in the retardation layer, the total content of the specific acid and a salt thereof in the retardation layer is not particularly limited, but from the viewpoint that the wet heat resistance of the optical film is more excellent, the total content is preferably 0.10% to 5.00% by mole, and more preferably 0.20% to 2.50% by mole, with respect to the liquid crystal compound represented by Formula (I) used for the formation of the retardation layer. In addition, the specific amount of the total content of the specific acid and a salt thereof in the retar› dation layer is preferably 0.25 to 12.3 nmol/cm 2 . 

[0075] Moreover, for example, in a case where only the specific acid is included and a salt of the specific acid is not included in the alignment layer, the total content is calcu› lated, considering the content of a salt of the specific acid in the alignment layer as 0. 

[0076] The specific acid is an acid having the pKa of -10.0 or less. 

[0077] The pKa of the specific acid is any value of -10.0 or less, and from the viewpoint that the wet heat resistance of the optical film is more excellent, the pKa is preferably -11.0 or less, and more preferably -12.0 or less. The lower limit is not particularly limited, but from the viewpoint that the wet heat resistance of the optical film is more excellent, the lower limit is preferably -20.0 or more, and more preferably -18.0 or more. 

[0078] A salt of the specific acid is a compound in which one or more hydrogen ions included in the specific acid are substituted with cations such as metal ions and ammonium ions. The salt may be either a so-called inorganic or an organic salt. 

[0079] The type of the metal ion is not particularly limited, and examples of the metal ion include an ion of a metal selected from the group consisting of an alkali metal and an alkaline earth metal. 

[0080] Examples of the ammonium ion include NH$_{4 }$ + and N(R)$_{4 }$ + (R represents a hydrocarbon group). 

[0081] The pKa is an acid dissociation constant, and a smaller value thereof indicates a higher acid strength. 

[0082] In the present specification, the pKa is calculated based on the following procedures (i) to (iv). That is, in a case where the pKa of the specific acid can be calculated in (i), the pKa calculated with (i) is taken as the pKa of the specific acid. In a case where the pKa cannot be calculated with (i), a trial of calculation of the pKa is made with (ii), and in a case where the pKa can be calculated with (ii), the value is taken as the pKa of the specific acid. In addition, in a case where the pKa cannot be calculated with (ii), a trial of calculation of the pKa is made with (iii), and in a case where the pKa can be calculated with (iii), the value is taken as the pKa of the specific acid. Further, in a case where the pKa cannot be calculated with (iii), a trial of calculation of the pKa is made with (iv), and in a case where the pKa can be calculated with (iv), the value is taken as the pKa of the specific acid. 

[0083] (i) The pKa value based on a Hammett substituent constant and the database of values in a well-known docu› ment is determined by computation using the following software package 1. 

[0084] (Software Package 1) 

[0085] Advanced Chemistry Development (ACD/Labs) Software VS.14 for Solaris (1994-2007 ACD/Labs). 

[0086] As the pKa of a superacid which is computable with the software package 1, a value obtained by rounding 

