Mold release film, process for its production, and process for producing semiconductor package

1. A mold release film comprising:

a resin-side release layer to be in contact with a curable resin at the time of curing the curable resin; and

a gas barrier layer,

wherein the gas barrier layer comprises a polymer (1) comprising:

vinyl alcohol units;

vinyl acetate units; and

units other than vinyl alcohol units or vinyl acetate units, which are at least one selected from the group consisting of units having a dihydroxy alkyl group, units having an acetoacetyl group, units having an oxyalkylene group, units having a carboxy group, units having an alkoxycarbonyl group, and units derived from an olefin, and

wherein the thickness of the gas barrier layer is from 0.1 to 5 μm.

2. The mold release film according to claim 1 , wherein the units other than vinyl alcohol units or vinyl acetate units, are represented by formula (1):

wherein:

R 1 to R 6 are each independently a hydrogen atom or a monovalent organic group; and

X is a single bond or a bonding chain.

3. The mold release film according to claim 1 , wherein

the polymer (I) has a crosslinked structure.

4. The mold release film according to claim 3 , wherein the insolubility degree of the gas barrier layer obtainable by the following formula from the basis weight W1 (g/m 2 ) of the gas barrier layer and the basis weight W2 (g/m 2 ) of the gas barrier layer remaining after subjecting the mold release film to a dissolution test, is from 10 to 80%:

Insolubility degree (%)=( W 2/ W 1)×100.

provided that the dissolution test is conducted by heating the mold release film for 1 hour by immersing the mold release film in ion-exchanged water of 80° C., during which stirring for 1 minute is repeated at 30 minutes intervals; then by washing the mold release film by immersing the mold release film in ion-exchanged water of 80° C. for 10 minutes which is different from the ion-exchanged water used in the heating; then by immersing the mold release film in ion-exchanged water of from 20 to 25° C. for 10 minutes to wash and cool the mold release film; and then by vacuum-drying the mold release film at 100° C. for 2 hours.

5. The mold release film according to claim 1 , wherein the thickness of the resin-side release layer is from 12 to 100 μm.

6. The mold release film according to claim 1 , wherein the resin-side release layer comprises a fluororesin.

7. The mold release film according to claim 6 , wherein the fluororesin is an ethylene-tetrafluoroethylene copolymer.

8. The mold release film according to claim 1 , wherein the mold release film has a two-layer structure of the resin-side release layer and the gas barrier layer.

9. A process for producing the mold release claim 1 , the process comprising:

applying a gas barrier layer-forming coating liquid on one surface of a substrate comprising the resin-side release layer to form a coating film, the gas barrier layer-forming coating liquid comprising the polymer (I) and a liquid medium; and

drying the coating film to form the gas barrier layer.

10. The process for producing the mold release film according to claim 9 , wherein:

the gas barrier layer-forming coating liquid further comprises a crosslinking agent; and

after forming the coating film, the polymer (I) is crosslinked with the crosslinking agent to form a cross-linked structure.

11. The process for producing the mold release film according to claim 10 , wherein an amount of the crosslinking agent in the gas barrier layer-forming coating liquid is from 1 to 20 mass % with respect to an amount of the polymer (I).

12. The process for producing the mold release film according to claim 9 , wherein

the liquid medium is an aqueous medium.

13. A process for producing a semiconductor package, comprising:

disposing the mold release film of claim 1 , on a surface of a mold which is to be in contact with a curable resin;

disposing a substrate having a semiconductor element mounted thereon, in the mold, and filling the curable resin in a space in the mold,

curing the curable resin to form a resin sealed portion, thereby obtaining a sealed body comprising the substrate, the semiconductor element and the resin sealed portion; and

releasing the sealed body from the mold.