Method for producing plastic products having grained surface thereon

A method for producing a plastic product having a grained surface, comprising:

• heating a thermoplastic sheet to a first temperature;
• placing the heated thermoplastic sheet between a first die and a second die having a grain pattern thereon, wherein the second die is provided with a plurality of minute holes extending therethrough and configured to be substantially uniformly distributed over an inner bottom surface thereof, and wherein the plurality of minute holes are connected to a vacuum tank through a passage controlled by a valve;
• warming the first die and the second die to a second temperature substantially lower than the first temperature, wherein the warming is at least partially independent from the heat supplied by the heating of the thermoplastic sheet and the thermoplastic molten plastic material;
• closing the first die and the second die such that the thermoplastic sheet is pushed by the first die toward the second die, and is deformed to conform to the first die and the second die;
• opening the valve rapidly to supply a predetermined vacuum pressure in the vacuum tank to the plurality of the minute holes substantially uniformly and simultaneously, while the first die and the second die are closed, wherein the vacuum tank is pumped to the predetermined vacuum pressure in advance;
• retreating the first die by a predetermined distance such that space is formed between the first die and the thermoplastic sheet;
• injecting thermoplastic molten plastic material in between the thermoplastic sheet and the first die;
• re-closing the first die and the second die;
• and
• cooling the injected thermoplastic molten plastic material such that the plastic product is formed by integrating thermoplastic sheet and the injected thermoplastic molten plastic material,
• wherein the second temperature is substantially lower than a surface temperature of the thermoplastic sheet.