Gas barrier film

1. A gas barrier film, comprising:

a single layer polyester resin film base material consisting of polybutylene terephthalate or a mixture of polybutylene terephthalate and polyethylene terephthalate with a content of the polybutylene terephthalate in the mixture being 60% mass or more, the polyester resin film base material has a first surface and a second surface, which is opposite to the first surface;

an anchor layer directly on the first surface of the single layer polyester resin film base material;

an AlO x layer or a SiO x layer having a thickness of no less than 5 nm and no greater than 100 nm directly on the anchor layer; and

a gas barrier protective layer on the AlO x layer or on the SiO x layer, the gas barrier protective layer comprises a hydrolysate of a metal alkoxide and polyvinyl alcohol,

wherein the gas barrier film has a heat shrinkage rate in the machine direction (MD direction) after heating for 30 minutes at 150° C. of 0.6% or more but less than 3.0%, the heat shrinkage rate being represented by the following formula:

Heat shrinkage rate={(Length before heating−Length after heating)/Length before heating}×100(%).

2. The gas barrier film of claim 1 , wherein a thickness of the film base material is no less than 6 μm and no greater than 200 μm.

3. The gas barrier film of claim 1 , wherein a puncture strength of the film base material is 8.5 N or more.

4. The gas barrier film of claim 1 , wherein the metal alkoxide is tetraethoxysilane.

5. The gas barrier film of claim 4 , wherein the polyester resin film base material consists of the mixture of polybutylene terephthalate and polyethylene terephthalate.

6. The gas barrier film of claim 5 , wherein the heat shrinkage rate in the machine direction (MD direction) of the gas barrier film is from 0.9% to 2.3%.

7. The gas barrier film of claim 1 , wherein the anchor layer consists of acrylic urethane resin or polyester polyurethane resin.

8. The gas barrier film of claim 1 , wherein the metal alkoxide is tetraethoxysilane and triisopropoxy aluminum.

9. A gas barrier film, comprising:

a single layer polyester resin film base material consisting of polybutylene terephthalate or a mixture of polybutylene terephthalate and polyethylene terephthalate with a content of the polybutylene terephthalate in the mixture being 60% mass or more, the polyester resin film base material has a first surface and a second surface, which is opposite to the first surface;

an anchor layer directly on the first surface of the single layer polyester resin film base material; and

an AlO x layer or a SiO x layer having a thickness of no less than 5 nm and no greater than 100 nm directly on the anchor layer; and

a gas barrier protective layer on the AlO x layer or the SiO x layer; the gas barrier protective layer comprises a hydrolysate of a metal alkoxide and polyvinyl alcohol,

wherein the gas barrier film has a tensile elasticity modulus within a range of 2.0 to 4.0 GPa, and a heat shrinkage rate in the machine direction (MD direction) after heating for 30 minutes at 150° C. of 0.6% or more but less than 3.0%, the heat shrinkage rate being represented by the following formula:

Heat shrinkage rate={(Length before heating−Length after heating)/Length before heating}×100(%).

10. The gas barrier film of claim 9 , wherein the metal alkoxide is tetraethoxysilane.

11. The gas barrier film of claim 9 , wherein the anchor layer consists of acrylic urethane resin or polyester polyurethane resin.

12. The gas barrier film of claim 9 , wherein the metal alkoxide is tetraethoxysilane and triisopropoxy aluminum.