POLYOXYMETHYLENE FILM AND PREPARATION METHOD THEREOF

Abstract

The invention is a polyoxymethylene film and a preparation method. The polyoxymethylene film comprises: 96 to 98 parts by weight of polyoxymethylene resin, 0.5 to 2 parts by weight of nucleating agent, 0.5 to 1 parts by weight of antioxidant, and 0.5 to 1 parts by weight of formaldehyde absorbent. In view of the high crystallinity and fast crystallization rate of polyoxymethylene, blown film process is used to directly blowing the molten mass extruded through a die of a screw extruder to form a blown film bubble. It is easy to form thin neck and easy to break when stretching, so the method is beneficial to form polyoxymethylene film, and has high processing efficiency, and is suitable for industrialization. Copolymerization unit CH.sub.2CH.sub.2O is introduced into the molecular chain of polyoxymethylene and its ratio is increased, thereby effectively reducing the crystallization rate of the materials and making it easier to form a film.

Claims

1. A method for preparing polyoxymethylene film, the polyoxymethylene film comprising: 96 to 98 parts by weight of polyoxymethylene resin, 0.5 to 2 parts by weight of nucleating agent, 0.5 to 1 parts by weight of antioxidant, and 0.5 to 1 parts by weight of formaldehyde absorbent, wherein the polyoxymethylene resin has a molecular formula of (CH.sub.2O).sub.n(CH.sub.2CH.sub.2O).sub.m, wherein (CH.sub.2CH.sub.2O).sub.m are copolymerization units accounting for a molar ratio 3% to 30%, the method comprising the following steps: (1) forming a mixture by putting the above parts by weight of the polyoxymethylene, the nucleating agent, the antioxidant, and the formaldehyde absorbent into a high-speed mixer and mixing them uniformly; (2) forming a tube by placing the mixture into a hopper of a screw extruder, melting the mixture to obtain a molten mass, and extruding the molten mass through a die; (3) forming polyoxymethylene films by a blown film process, comprising stretching the tube upward and blowing compressed air into the tube to form a blown film bubble, and simultaneously cooling the blown film bubble by using a multistage air cooling ring around the outer surface of the bubble, then collapsing the cooled blown film bubble by passing through a collapsing frame and thereafter through pulling rollers, then solidifying, cutting and winding onto rolls.

2. The method of claim 1, wherein, in the step (2), the screw extruder has a temperature of 170 C. to 185 C. at a feeding section, 190 C. to 200 C. at a plasticization section, 195 C. to 210 C. at a homogenization section, and 205 C. to 220 C. at a filter mesh, and the die has a temperature of 205 C. to 220 C., and the screw extruder has a screw rotation speed of 40 r/min.

3. The method of claim 1, wherein, in the step (3), the blown film bubble has a Blown Up Ratio of 1.4 to 2.5 and a Stretch Ratio of 2 to 4, and the pulling rollers have a speed of 1224 m/min.

4. The method of claim 1, wherein, in the step (3), the multistage air cooling ring comprises at least 3 air cooling rings to perform step-by-step slow cooling, the temperature of which are gradually decreased from bottom to top in the axial direction.

5. The method of claim 4, wherein, in the step (3), the temperature of the 3 air cooling rings are 160 C. to 140 C., 130 C. to 100 C. and 80 C. to 30 C. respectively.

6. The method of claim 5, wherein, in the step (3), the air cooling ring with the temperature of 160 C. to 140 C. preferably has an axial length of 10 mm, the air cooling ring with the temperature of 130 C. to 100 C. has an axial length of 10 mm, and the air cooling ring with the temperature of 80 C. to 30 C. has an axial length of 8 mm, and each of the air cooling rings has an air pressure of 0.2 MPa to 0.4 MPa.

7. The method of claim 1, wherein, the polyoxymethylene resin has a melt index of 3 to 13 g/10 min.

8. The method of claim 1, wherein, the nucleating agent is selected from the group consisting of polytetrafluoroethylene, polyvinylidene fluoride powder, and a mixture thereof.

9. The method of claim 1, wherein, the formaldehyde absorbent is selected from the group consisting of melamine, hexamethylenediamine formaldehyde polycondensate, dicyandiamide, and a mixture thereof.

10. A polyoxymethylene film prepared by the method according to claim 1.

11. A polyoxymethylene film prepared by the method according to claim 2.

12. A polyoxymethylene film prepared by the method according to claim 3.

13. A polyoxymethylene film prepared by the method according to claim 4.

14. A polyoxymethylene film prepared by the method according to claim 5.

15. A polyoxymethylene film prepared by the method according to claim 6.

16. A polyoxymethylene film prepared by the method according to claim 7.

17. A polyoxymethylene film prepared by the method according to claim 8.

18. A polyoxymethylene film prepared by the method according to claim 9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 shows the spherulite size of polyoxymethylene in which the copolymerization unit accounts for 10%.

[0021] FIG. 2 shows the spherulite size of polyoxymethylene in which the copolymerization unit accounts for 10% and a nucleating agent is added.

[0022] FIG. 3 is a graph showing the crystallinity-time curve of polyoxymethylene with different proportions of copolymerization units.

DETAILED DESCRIPTION OF EMBODIMENTS

[0023] The present invention will now be described in detail with reference to the embodiments, but the invention is not limited to the following embodiments.

Embodiment 1

[0024] The polyoxymethylene film in present embodiment is prepared by the following preparation method at the following raw material ratio.

[0025] The polyoxymethylene film comprises: 98 parts by weight of polyoxymethylene resin, 1 parts by weight of polyvinylidene fluoride, 0.5 parts by weight of antioxidant, and 0.5 parts by weight of melamine, wherein (CH.sub.2CH.sub.2O).sub.m copolymerization units account for a molar ratio 3% in the polyoxymethylene molecular structure.

[0026] A method for preparing polyoxymethylene film comprises the following steps:

[0027] (1) forming a mixture by putting the above parts by weight of the polyoxymethylene resin having a melt index of 13 g/10 min, the polyvinylidene fluoride, the antioxidant, and the melamine into a high-speed mixer and mixing them uniformly;

[0028] (2) forming a tube by placing the mixture into a hopper of a screw extruder, melting the mixture to obtain a molten mass, and extruding the molten mass through a die;

[0029] (3) forming polyoxymethylene films by a blown film process, comprising stretching the tube upward and blowing compressed air into the tube to form a blown film bubble, and simultaneously cooling the blown film bubble by using a multistage air cooling ring around the outer surface of the bubble, then collapsing the cooled blown film bubble by passing through a collapsing frame and thereafter through pulling rollers, then solidifying, cutting and winding onto rolls.

[0030] Parameters of the process are as follows: in the step (2), the screw extruder has a temperature of 170 C. to 185 C. at a feeding section, 190 C. to 200 C. at a plasticization section, 195 C. to 210 C. at a homogenization section, and 205 C. to 220 C. at a filter mesh, and the die has a temperature of 205 C. to 220 C., and the screw extruder has a screw rotation speed of 40 r/min; in the step (3), the blown film bubble has a Blown Up Ratio of 1.4 and a Stretch Ratio of 2, and the pulling rollers have a speed of 12 m/min, and the temperature of the 3 air cooling rings are 160 C., 130 C. and 80 C. respectively, and the air cooling ring with the temperature of 160 C. has an axial length of 10 mm, the air cooling ring with the temperature of 130 C. has an axial length of 10 mm, and the air cooling ring with the temperature of 80 C. has an axial length of 8 mm, and each of the air cooling ring has an air pressure of 0.4 MPa.

Embodiment 2

[0031] The polyoxymethylene film in present embodiment is prepared by the following preparation method at the following raw material ratio.

[0032] The polyoxymethylene film comprises: 97.5 parts by weight of polyoxymethylene resin, 0.5 parts by weight of polyvinylidene fluoride, 1 parts by weight of antioxidant, 0.5 parts by weight of melamine, and 0.5 parts by weight of dicyanodiamide, wherein (CH.sub.2CH.sub.2O).sub.m are copolymerization units accounting for a molar ratio 10% in the polyoxymethylene molecular structure.

A method for preparing polyoxymethylene film comprises the following steps:

[0033] (1) forming a mixture by putting the above parts by weight of the polyoxymethylene resin having a melt index of 9 g/10 min, the polyvinylidene fluoride, the antioxidant, and the melamine into a high-speed mixer and mixing them uniformly;

[0034] (2) forming a tube by placing the mixture into a hopper of a screw extruder, melting the mixture to obtain a molten mass, and extruding the molten mass through a die;

[0035] (3) forming polyoxymethylene films by a blown film process, comprising stretching the tube upward and blowing compressed air into the tube to form a blown film bubble, and simultaneously cooling the blown film bubble by using a multistage air cooling ring around the outer surface of the bubble, then collapsing the cooled blown film bubble by passing through a collapsing frame and thereafter through pulling rollers, then solidifying, cutting and winding onto rolls.

[0036] Parameters of the process are as follows: in the step (2), the screw extruder has a temperature of 170 C. to 185 C. at a feeding section, 190 C. to 200 C. at a plasticization section, 195 C. to 210 C. at a homogenization section, and 205 C. to 220 C. at a filter mesh, and the die has a temperature of 205 C. to 220 C., and the main engine of the single screw extruder has a screw rotation speed of 40 r/min; in the step (3), the blown film bubble has a Blown Up Ratio of 2 and a Stretch Ratio of 3, and the pulling rollers have a speed of 18 m/min, and the temperature of the 3 air cooling rings are 150 C., 120 C. and 60 C. respectively, and the air cooling ring with the temperature of 150 C. has an axial length of 10 m, the air cooling ring with the temperature of 120 C. has an axial length of 10 mm, and the air cooling ring with the temperature of 60 C. has an axial length of 8 mm, and each of the air cooling ring has an air pressure of 0.2 MPa.

Embodiment 3

[0037] The polyoxymethylene film in present embodiment is prepared by the following preparation method at the following raw material ratio.

[0038] The polyoxymethylene film comprises: 96 parts by weight of polyoxymethylene resin, 1 parts by weight of polytetrafluoroethylene, 1 parts by weight of polyvinylidene fluoride, 1 parts by weight of antioxidant, and 1 parts by weight of hexanediamine formaldehyde polycondensation, wherein (CH.sub.2CH.sub.2O).sub.m are copolymerization units accounting for a molar ratio 20% in the polyoxymethylene molecular structure.

[0039] A method for preparing polyoxymethylene film having high barrier resistance comprises the following steps:

[0040] (1) forming a mixture by putting the above parts by weight of the polyoxymethylene resin having a melt index of 3 g/10 min, the polytetrafluoroethylene, the antioxidant, and the hexanediamine formaldehyde polycondensation into a high-speed mixer and mixing them uniformly;

[0041] (2) forming a tube by placing the mixture into a hopper of a screw extruder, melting the mixture to obtain a molten mass, and extruding the molten mass through a die;

[0042] (3) forming polyoxymethylene films by a blown film process, comprising stretching the tube upward and blowing compressed air into the tube to form a blown film bubble, and simultaneously cooling the blown film bubble by using a multistage air cooling ring around the outer surface of the bubble, then collapsing the cooled blown film bubble by passing through a collapsing frame and thereafter through pulling rollers, then solidifying, cutting and winding onto rolls.

[0043] Parameters of the process are as follows: in the step (1), the screw extruder has a temperature of 170 C. to 185 C. at a feeding section, 190 C. to 200 C. at a plasticization section, 195 C. to 210 C. at a homogenization section, and 205 C. to 220 C. at a filter mesh, and the die has a temperature of 205 C. to 220 C., and the main engine of the single screw extruder has a screw rotation speed of 40 r/min; in the step (2), the blown film bubble has a Blown Up Ratio of 2.5 and a Stretch Ratio of 4, and the pulling rollers have a speed of 24 m/min, and the temperature of the 3 air cooling rings are 150 C., 100 C. and 30 C. respectively, and the air cooling ring with the temperature of 150 C. has an axial length of 10 mm, the air cooling ring with the temperature of 100 C. has an axial length of 10 mm, and the air cooling ring with the temperature of 30 C. has an axial length of 8 mm, and each of the air cooling ring has an air pressure of 0.4 MPa.

Embodiment 4

[0044] The polyoxymethylene film in present embodiment is prepared by the following preparation method at the following raw material ratio.

[0045] The polyoxymethylene film comprises: 96 parts by weight of polyoxymethylene resin, 1 parts by weight of polytetrafluoroethylene, 1 parts by weight of polyvinylidene fluoride, 1 parts by weight of antioxidant, and 1 parts by weight of hexanediamine formaldehyde polycondensation, wherein (CH.sub.2CH.sub.2O).sub.m are copolymerization units accounting for a molar ratio 30% in the polyoxymethylene molecular structure.

[0046] A method for preparing polyoxymethylene film having high barrier resistance comprises the following steps:

[0047] (1) forming a mixture by putting the above parts by weight of the polyoxymethylene resin having a melt index of 3 g/10 min, the polytetrafluoroethylene, the antioxidant, and the hexanediamine formaldehyde polycondensation into a high-speed mixer and mixing them uniformly;

[0048] (2) forming a tube by placing the mixture into a hopper of a screw extruder, melting the mixture to obtain a molten mass, and extruding the molten mass through a die;

[0049] (3) forming polyoxymethylene films by a blown film process, comprising stretching the tube upward and blowing compressed air into the tube to form a blown film bubble, and simultaneously cooling the blown film bubble by using a multistage air cooling ring around the outer surface of the bubble, then collapsing the cooled blown film bubble by passing through a collapsing frame and thereafter through pulling rollers, then solidifying, cutting and winding onto rolls.

[0050] Parameters of the process are as follows: in the step (1), the screw extruder has a temperature of 170 C. to 185 C. at a feeding section, 190 C. to 200 C. at a plasticization section, 195 C. to 210 C. at a homogenization section, and 205 C. to 220 C. at a filter mesh, and the die has a temperature of 205 C. to 220 C., and the main engine of the single screw extruder has a screw rotation speed of 40 r/min; in the step (2), the blown film bubble has a Blown Up Ratio of 2.5 and a Stretch Ratio of 4, and the pulling rollers have a speed of 24 m/min, and the temperature of the 3 air cooling rings are 140 C., 100 C. and 30 C. respectively, and the air cooling ring with the temperature of 140 C. has an axial length of 10 mm, the air cooling ring with the temperature of 100 C. has an axial length of 10 mm, and the air cooling ring with the temperature of 30 C. has an axial length of 8 mm, and each of the air cooling ring has an air pressure of 0.4 MPa.

[0051] The performance parameters of the polyoxymethylene films prepared in the embodiments of the present invention are shown in Table 1.

TABLE-US-00001 TABLE 1 Performance parameters of the polyoxymethylene films Embodiment No. Performance parameters 1 2 3 4 Film thickness/m 300 140 30 30 Mean variation of film thickness/% 13 11 10 9 Coefficient of dynamic friction 0.16 0.13 0.11 0.11 Transverse tensile strength/MPa 76 83 113 108 Longitudinal tensile strength/MPa 78 91 98 93

[0052] The effect of the ratio of copolymerization units on the semi-crystallization time of polyoxymethylene is shown in Table 2.

TABLE-US-00002 TABLE 2 Semi-crystallization time of polyformaldehyde with different ratios of copolymerization units Samples 3% 10% 15% 20% 30% t (S) 115 121 132 135 142