DIFFRACTION OPTICAL ELEMENT FORMATION ACRYLIC RESIN COMPOSITION

To provide a diffraction optical element that has resistance to sticking under a heat and humidity condition and causes less pattern deformation, a method for manufacturing the diffraction optical element, an acrylic resin composition for forming a diffraction optical element, and an illumination device.SOLUTION: The diffraction optical element shapes light from a light source, and has a diffraction grating unit including at least one high refractive index protruding part protruding from the surface of a transparent base material to at least one surface side of a transparent base material and at least one low refractive index part. The high refractive index protruding part is made of a cured material of the acrylic resin composition, and has a storage elastic modulus (E') of 0.90×109 Pa to 2.6×109 Pa, both inclusive, when the temperature and the relative moisture of the cured material are 60°C and 95%.SELECTED DRAWING: Figure 2 【課題】湿熱条件下における耐スティッキング性を有し、かつパターンもげの少ない回折光学素子及びその製造方法、回折光学素子形成用のアクリル系樹脂組成物、並びに照明装置を提供する。【解決手段】光源からの光を整形する回折光学素子であって、透明基材の少なくとも一面側に、透明基材の表面から突出する一つ以上の高屈折率凸部と、一つ以上の低屈折率部とを配置した回折格子部を備えており、前記高屈折率凸部は、アクリル系樹脂組成物の硬化物で形成されており、当該硬化物の６０℃かつ相対湿度９５％における貯蔵弾性率（Ｅ'）が、０．９０×１０９Ｐａ以上２．６×１０９Ｐａ以下である、回折光学素子。【選択図】図２