Isocyanate-based adhesive
An embodiment of the present technology is an isocyanate-based adhesive used for a surface-treated crystalline thermoplastic resin base material, the isocyanate-based adhesive having a value represented by (JIS-A hardness)/(strength at break [MPa])×(elongation at break (%))/100 of 2.0 to 70 after being cured by being allowed to stand still under a condition at 23° C. and 50% RH for 3 days, and the crystalline thermoplastic resin base material having a value represented by (δ d /δ p +δ p ) of 2.0 to 30.0. δ p =γ p −γ p0 and δ d =|γ d −γ d0 |, γ p0 is a polar term of surface free energy before the surface treatment, γ p is a polar term of surface free energy after the surface treatment, γ d0 is a dispersion term of the surface free energy before the surface treatment, and γ d is a dispersion term of the surface free energy after the surface treatment.
1. An isocyanate-based adhesive used for a surface-treated crystalline thermoplastic resin base material, the isocyanate-based adhesive comprising:
a main agent containing a urethane prepolymer; and
a curing agent containing a tri- or higher functional polyol having a weight average molecular weight of 1000 or less,
wherein:
a ratio of a mixed amount of the curing agent to a mixed amount of the main agent is, in terms of mass ratio, 1.1 or less,
the isocyanate-based adhesive contains no terpene compounds,
the isocyanate-based adhesive has a value represented by Formula (A) of 2.0 to 70 after being cured by being allowed to stand still under a condition at 23° C. and 50% RH for 3 days, and
the crystalline thermoplastic resin base material has a value represented by Formula (B) of 2.0 to 30.0:
Formula ( A )=(JIS-A hardness)/(strength at break [MPa])×(elongation at break (%))/100
Formula ( B )=δ d /δ p +δ p
where δ p =γ p −γ p0 and δ d =|γ d −γ d0 |,
γ p0 is a polar term of surface free energy of a crystalline thermoplastic resin base material before the surface treatment,
γ p is a polar term of the surface free energy of the crystalline thermoplastic resin base material after the surface treatment,
γ d0 is a dispersion term of the surface free energy of the crystalline thermoplastic resin base material before the surface treatment, and
γ d is a dispersion term of the surface free energy of the crystalline thermoplastic resin base material after the surface treatment.
2. The isocyanate-based adhesive according to claim 1 , wherein the isocyanate-based adhesive contains at least one aliphatic isocyanate modified product selected from the group consisting of isocyanurates of aliphatic isocyanates, allophanates of aliphatic isocyanates, and biurets of aliphatic isocyanates.
3. The isocyanate-based adhesive according to claim 1 , wherein the isocyanate-based adhesive contains a silane coupling agent.
4. The isocyanate-based adhesive according to claim 1 , wherein the isocyanate-based adhesive contains carbon black or calcium carbonate.
5. The isocyanate-based adhesive according to claim 2 , wherein the isocyanate-based adhesive contains a silane coupling agent.
6. The isocyanate-based adhesive according to claim 2 , wherein the isocyanate-based adhesive contains carbon black or calcium carbonate.
7. The isocyanate-based adhesive according to claim 3 , wherein the isocyanate-based adhesive contains carbon black or calcium carbonate.
8. The isocyanate-based adhesive according to claim 5 , wherein the isocyanate-based adhesive contains carbon black or calcium carbonate.