JPH05293821A - Manufacture of differential pressure forming crystalline polypropylene sheet - Google Patents

Abstract

PURPOSE:To obtain polypropylene sheet, the sagging at the heating for differential pressure forming of which is small and out of which a vessel excellent in the uniformity of wall thickness and impact strength can be obtained, by a method wherein ultrahigh molecular weight crystalline polypropylene power having specified intrinsic viscosity is turned into sheet with revolving rolls, the temperature of which is set within the specified temperature range above its melting point. CONSTITUTION:The crystalline polypropylene used for the manufacturing method concerned has intrinsic viscosity in tetralin at 140 deg.C of 4-50dl/g. The polypropylene powder is continuously compression-molded into sheet with one pair of a plurality of pairs of metal pinch rolls 5-8. At this time, the surface temperature of the rolls 5-8 is set to be higher than its crystalline melting point (Tm) and lower than Tm+110 deg.C. Tm is the crystalline melting end temperature of the DSC curve obtained when the temperature is raised at the rate of 5 deg.C/min. If the surface temperature of the rolls is help below Tm, the mechanical strength of the formed article made of the obtained sheet is remarkably low. If the surface temperature of the rolls is held above Tm+110 deg.C, the stable forming of the obtained sheet becomes impossible.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a sheet excellent in differential pressure moldability from a thermoplastic resin powder containing a crystalline polypropylene polymer powder of ultra-high molecular weight which cannot be melt-extruded as a main component. Is provided. Tray and container obtained by so-called differential pressure forming such as vacuum forming or pressure forming using this sheet are useful as food packaging containers and various containers having excellent wall thickness uniformity, impact strength and heat resistance.

[0002]

2. Description of the Related Art Polyvinyl chloride, high impact polystyrene (HIPS), ABS, biaxially oriented polystyrene, expanded polystyrene (PSP), etc. are used for differential pressure molded products such as egg trays, fruit trays, confectionery trays and meat trays. A large amount of amorphous resin is used. Slightly considering the food hygiene, heat resistance, oil resistance, and chemical resistance, a chocolate tray, an IC element tray, and an electronic tray made of crystalline polypropylene having a melt flow rate (MFR) of 0.1 to 4 g / 10 min. A range cooking tray is used.

This is because the amorphous resin is superior in bending rigidity to polypropylene and can reduce the wall thickness of the tray and the container, and the sheet melted at the time of sheet heating at the time of differential pressure molding is sagged in the direction of gravity. It is possible to increase the molding cycle and the cost is low. This is because crystalline polypropylene has a large sheet sag, a dedicated differential pressure molding machine is required, and the molding cycle is slow (Japanese Patent Laid-Open Nos. 47-22466 and 47-224).
No. 65).

Several methods have been proposed to improve the problem of sagging of the crystalline polypropylene sheet and to obtain a container having an excellent wall thickness distribution. For example, JP-A-54-
In 86586, MFR is 0.21 to 1.5 g /
It has been proposed to use polypropylene having a wide molecular weight distribution at 10 minutes, but it does not essentially solve the sagging during heating of the sheet.

Further, in JP-A-53-66952, in order to improve sagging during heating after forming crystalline polypropylene into a sheet by extrusion molding,
A method of pressure forming at a temperature lower than the melting point has been proposed, but the degree of freedom of the shape of the molded product is small, and it is limited to the case of a simple shape.

[0006]

DISCLOSURE OF THE INVENTION The present invention is a method for producing a polypropylene sheet which gives a container excellent in wall thickness uniformity and impact strength with less sagging of the crystalline polypropylene sheet in the step of heating the sheet during differential pressure molding. For the purpose of providing.

[0007]

According to the present invention, a crystalline polypropylene polymer powder having an intrinsic viscosity in 140 ° C. tetralin of 4 to 50 dl / g is melted at a temperature not lower than the DSC curve peak of the powder. End temperature + 110 ℃
Of a crystalline polypropylene sheet for differential pressure molding, characterized in that the sheet is shaped by continuous constriction transfer by one or a plurality of pairs of rotating rolls whose surface temperature is set to a temperature not higher than It provides a method.

[0008]

[Function] Ultra-high molecular weight crystalline polypropylene, which has an extremely high melt viscosity, is used as the sheet material, so the decrease in the melt viscoelasticity of the sheet during heating is small, so the sheet sag is small and differential pressure molding with an excellent wall thickness distribution Goods are obtained.

Crystalline Polypropylene Polymer The ultrahigh molecular weight crystalline polypropylene polymer used in the present invention has an intrinsic viscosity of 4 to 140 ° C. in tetralin.
It is a crystalline polypropylene polymer of 50 dl / g. Even if this polymer is a propylene homopolymer, it contains 50 mol% of propylene and one or more olefins such as ethylene, butene-1, 4-methylpentene-1, and hexene-1. It may be a random copolymer or a block copolymer.

Further, it may be a mixture of these,
Styrene, acrylic acid, maleic anhydride,
Itaconic acid and an epoxy compound may be graft-copolymerized. This ultra-high molecular weight crystalline polypropylene polymer powder is produced by the same polymerization method as that of ordinary polypropylene (Plastic Age 199).
March 0, 36, 137-144).

0.05 to 5% by weight of additives such as an antioxidant, a pigment, a dispersant, an antistatic agent and a lubricant are added to the polymer particles.
You may mix. In addition, the other melt flow rates are 0.
1-50g / 10min polypropylene, polyethylene,
Ordinary thermoplastic resin such as nylon may be blended in an amount of 50% by weight or less. The average particle size of the ultra-high molecular weight crystalline polypropylene polymer powder is generally 100 to 600 μm, but there is no strict restriction on the particle size.

Such a material containing ultra-high molecular weight polypropylene as a main component has a very high melt viscosity and cannot be formed into a sheet by extrusion molding. The present invention will be described below with reference to the drawings. 1 and 2 are
1 schematically shows an example of sheet manufacturing equipment in an embodiment of the present invention. FIG. 1 shows that the ultra high molecular weight polypropylene polymer powder (1) supplied is continuously compression-shaped by a pair of metal constriction transfer rolls (2, 3) heated to a proper temperature to form a sheet ( It is a method of forming a film (including a film) (4).

FIG. 2 shows that the supplied ultra high molecular weight polypropylene polymer powder (1) is continuously compression molded by a plurality of pairs of metal constriction transfer rolls (5, 6, 7, 8) heated to an appropriate temperature. This shows another embodiment of the present invention in which the sheet (4) is shaped by doing. The surface temperature of the metal constriction transfer roll (2,3,5,6,7,8) is a temperature of Tm or higher, where Tm is the crystal melting point obtained from the DSC curve of ultrahigh molecular weight crystalline polypropylene,
The temperature range is (Tm + 110 ° C.) or less.

Here, the crystal melting point means a differential thermal scanning meter (D
In the DSC curve (Fig. 3) obtained by heating 3 to 10 mg of polypropylene powder made of ultra-high molecular weight crystals at a rate of 5 ° C / min (SC), the melting end temperature Tm (right side of the peak) at which the crystals are completely melted Hem). When the surface temperature of the metal roll during the sheet manufacturing process is lower than the crystal melting point temperature (Tm) of polypropylene, the bond between the ultra-high molecular weight polypropylene polymer powders is weak, and the sheet manufactured at such a low temperature is used. The thermoformed molded product has remarkably reduced mechanical strength.

On the other hand, the surface temperature of the metal roll is (crystal melting point +
If the temperature is higher than 110 ° C.), the molten material adheres to the surface of the metal roll during the sheet processing step, making stable molding impossible.

[0016]

EXAMPLES The present invention will now be described in more detail with reference to Examples. In addition, the sheet drooping tester shown in FIG. 4 was used for the sheet drooping during the sheet heating step.

This tester has a structure in which a ceramic heater (10) is installed in the upper part of a heat insulating tank (9) whose front surface is transparent glass, and the surface temperature of the heater is detected by a thermocouple (11). There is. The measurement of the dripping of heat was performed after the surface of the ceramic heater (11) reached a predetermined temperature, and then the sheet-like sample (12) was measured by an internal method of 260 mm × 26.
It is quickly and horizontally installed in this tank while being fixed by a 0 mm frame (13), and the amount of sagging of the sheet center is measured by a pointer (14). The sagging property of the sheet during heating is such that the surface temperature of the heater is 460 ° C.
The sheet is quantified by the amount of sagging after 60 seconds have passed since it was placed in the tank.

Example 1 Intrinsic viscosity in tetralin at 140 ° C. was 7.5 dl.
/ G Ultra high molecular weight polypropylene polymer powder (Tm
= 168 ° C., T ₀ = 152 ° C.), the sheet was shaped into a sheet by the apparatus of FIG. In this case, the diameter of the rolls (2, 3) was 120 mmφ, the surface temperature of each roll was 220 ° C., and the rotation peripheral speed was 4.5 m / min.
Ultra high molecular weight polypropylene polymer powder can be rolled (2,
3) Constricted transfer by 0.7mm thickness, 500 width
mm sheets were obtained.

The amount of sagging of the sheet when heated was 3 mm. Asano Research Institute Co., Ltd. Vacuum / compressive differential pressure molding machine (Cosmic FXL-0
4; brand name), the sheet is passed through an oven set at 190 ° C. for 12 seconds to be heated and melted, and then 3.5 kg / cm ² G of compressed air, -450 mmHg of reduced pressure, plug assist vacuum. Pressure molding was performed to obtain a cup having the shape shown in FIG.

The wall thickness of each part in the molded container was measured by a digital micrometer manufactured by Mitoyo Co., Ltd. to evaluate the wall thickness unevenness. The wall thickness unevenness was quantified by the calculation of the following formula (I) from the wall thickness of the maximum wall thickness, the wall thickness of the minimum wall thickness, and the average wall thickness of the measured wall thickness of each portion in the container.

[0021]

[Equation 1]

The average wall thickness of the cup was 0.17 mm, the maximum wall thickness was 0.27 mm, the minimum wall thickness was 0.09 mm, and the wall thickness unevenness was 105%. ..
Also, by filling the container with water at room temperature to the opening portion and dropping vertically to the concrete floor at room temperature and observing the presence or absence of damage, the breaking limit drop height of the container (the container under the same manufacturing conditions) Was carried out at various drop heights, and the maximum height of the limit (not exceeding the limit) was 85 cm.

Example 2 The intrinsic viscosity in tetralin at 140 ° C. was 10.2 d.
Ultra high molecular weight polypropylene polymer powder (T / l)
m = 168 ° C., T ₀ = 152 ° C.) and a process similar to that in Example-1 to obtain a sheet having a thickness of 0.7 mm. The amount of sagging of the sheet during heating of the sheet was 2 mm. The average wall thickness of the cup obtained by molding this sheet in the same manner as in Example-1 was 0.17 mm, the wall thickness of the maximum wall portion was 0.26 mm, and the wall thickness of the minimum wall portion was 0. 09 m
m, thickness unevenness was 100%. The breaking limit drop height as a result of dropping test after filling with water was 100 cm.

Comparative Example-1 Intrinsic viscosity in tetralin at 140 ° C was 17.5d.
Ultra high molecular weight polypropylene polymer powder (T / l)
m = 168 ° C., T ₀ = 152 ° C.) was used to manufacture a sheet by the same steps as in Example 1 except that the surface temperature of the metal rolls (2, 3) was changed to 150 ° C. A proper sheet could not be obtained due to poor fusion between polymer powders.

Example 3 Intrinsic viscosity in tetralin at 140 ° C. was 17.5d.
Ultra high molecular weight polypropylene polymer powder (T / l)
m = 168 ° C., T ₀ = 152 ° C.) using a roll (2,
A sheet having a thickness of 0.7 mm was obtained in the same manner as in Example 1 except that the surface temperature of 3) was 175 ° C.

The amount of sagging of the sheet when heated was 0 mm. The average wall thickness of the cup obtained by molding this sheet in the same manner as in Example-1 was 0.1.
The thickness was 7 mm, the maximum thickness was 0.26 mm, the minimum thickness was 0.10 mm, and the thickness variation was 94%. The breaking limit drop height as a result of dropping test after filling with water was 110 cm.

Example 4 Intrinsic viscosity in tetralin at 140 ° C. was 17.5d.
Ultra high molecular weight polypropylene polymer powder (T / l)
m = 168 ° C., T ₀ = 152 ° C.) was used to form a sheet with the apparatus shown in FIG. In this case rolls (5, 6,
7, 8) had a diameter of 120 mmφ, and the surface temperature was 220 ° C. for the rolls (5, 6, 7) and 180 ° C. for the roll (8), and the rotational peripheral speed was 4.5 m / min. Ultra high molecular weight polypropylene polymer powder can be rolled (5, 6,
7 and 8), the sheet was narrowed and transferred to obtain a 1.1 mm-thick sheet.

The amount of sagging of the sheet during heating of the sheet was measured and found to be 0 mm. The average thickness of the cup obtained by molding this sheet in the same manner as in Example-1 was
0.25 mm, the maximum wall thickness is 0.40 m
m, the thickness of the minimum thickness part is 0.16 mm, the thickness unevenness is 9
It was 6%. The breaking limit drop height as a result of dropping test after filling with water was 170 cm.

Example 5 Intrinsic viscosity in tetralin at 140 ° C. was 17.5 dl.
/ G Ultra high molecular weight polypropylene polymer powder (Tm
= 168 ° C., T ₀ = 152 ° C.), the roll (5,
Example 7, except that the surface temperature of 6, 7) was 250 ° C.
A sheet having a thickness of 1.1 mm was obtained and molded in the same manner as in 4.

The amount of sagging of the sheet during heating of the sheet was 0 mm. The average wall thickness of the cup is 0.2
The thickness is 5 mm, the maximum thickness is 0.41 mm, the minimum thickness is 0.16 mm, and the thickness variation is 100%.
Met. The breaking limit drop height as a result of filling test with water and a drop test was 160 cm.

Example 6 The intrinsic viscosity in tetralin at 140 ° C. was 17.5 d.
Ultra high molecular weight polypropylene polymer powder (T / l)
m = 168 ° C., T ₀ = 152 ° C.) using a roll (5,
Example 7, except that the surface temperature of 6, 7) was 270 ° C.
A sheet with a thickness of 1.1 mm was obtained in the same manner as in 4, and a cup was molded.

The amount of sagging of the sheet when heated was 2 mm. The average wall thickness of the cup is 0.25
The thickness of the thickest portion was 0.40 mm, the thickness of the thinnest portion was 0.16 mm, and the thickness unevenness was 96%. The breaking limit drop height as a result of a drop test after filling with water was 155 cm.

Comparative Example-2 The intrinsic viscosity in 140 ° C. tetralin was 17.5 d.
Ultra high molecular weight polypropylene polymer powder (T / l)
m = 168 ° C., T ₀ = 152 ° C.) using a roll (5,
Example 7, except that the surface temperature of 6, 7) was 280 ° C.
An attempt was made to manufacture a sheet in the same manner as in No. 4, but the molten material adhered to the roll surface, and stable molding was impossible.

Example 7 The intrinsic viscosity in 140 ° C. tetralin was 21.5 d.
Ultra high molecular weight polypropylene polymer powder (T / l)
m = 168 ° C., T ₀ = 152 ° C.) using a roll (5,
Example 7-, except that the surface temperature of 6, 7) was 220 ° C.
A sheet having a thickness of 1.1 mmt was obtained in the same manner as in 4.

The amount of sagging of the sheet during heating of the sheet was 0 mm. The average wall thickness of the cup obtained by molding this sheet in the same manner as in Example-4 was 0.25 mm, the maximum wall thickness was 0.39 mm, and the minimum wall thickness was 0. It was 0.17 mm and the thickness unevenness was 88%. As a result of the drop test after filling with water, the breaking limit drop height is 1
It was 80 cm.

Comparative Example-3 The intrinsic viscosity in 140 ° C. tetralin was 3.8 dl.
/ G, MFR (JIS K 7210-1976, load 2.16 kg, 230 ° C.) is 0.1 g / 10 min, polypropylene polymer powder (Tm = 168 ° C., T ₀ = 15).
2 ℃) and the surface temperature of the roll (2,3) is 220 ℃
0.7 m in the same manner as in Example 1 except that
m sheets were obtained.

The amount of sagging of the sheet during heating of the sheet was 48 mm. The average wall thickness of the cup obtained from this sheet in the same manner as in Example-1 was 0.16 mm, the maximum wall thickness was 0.28 mm, and the minimum wall thickness was 0.07 mm. The thickness unevenness was 131%. The breaking limit drop height as a result of the drop test after filling with water is 45c.
It was m.

Comparative Example-4 The intrinsic viscosity in 140 ° C. tetralin was 3.8 dl.
/ G, MFR 0.1g / 10 minutes polypropylene polymer powder (Tm = 168 ℃, T ₀ = 152 ℃) was used except that the surface temperature of the roll (5,6,7) was 220 ℃ A sheet having a thickness of 1.1 mm was obtained in the same manner as in Example-4.

The amount of sagging of the sheet when heated was 61 mm. The average wall thickness of the cup obtained by molding this sheet is 0.24 mm, the maximum wall thickness is 0.44 mm, and the minimum wall thickness is 0.10 m.
m, thickness unevenness was 141%. The breaking limit drop height as a result of dropping test after filling with water was 80 cm.
The above results are shown in Table 1.

[0040]

[Table 1]

[0041]

[Effect] To provide a sheet which gives a molded article having a small sagging during heating of the sheet in the differential pressure molding step, excellent moldability, good wall thickness distribution and excellent impact strength.

[Brief description of drawings]

FIG. 1 is a plan view of a sheet manufacturing apparatus of the present invention.

FIG. 2 is a plan view of a sheet manufacturing apparatus according to another aspect of the present invention.

FIG. 3 is a DSC curve for polypropylene.

FIG. 4 is a plan view of an apparatus for measuring the height of sag when heating a sheet.

FIG. 5 is a cross-sectional view showing the dimensions of a differential pressure molded product (cup).

[Explanation of symbols]

1 Ultra high molecular weight polypropylene polymer powder 2,3 Metal constriction transfer roll 4 Sheet 5,6,7,8 Metal constriction transfer roll T ₀ Peak temperature of DSC curve of polypropylene T _m Crystal melting point of polypropylene 9 Insulation tank 10 Ceramic Heater 11 Thermocouple 12 Sample (sheet) 13 Seat fixing frame 14 Pointer

Claims (1)

[Claims] 1. A crystalline polypropylene polymer powder having an intrinsic viscosity of 4 to 50 dl / g in tetralin at 140 ° C. is at a temperature not lower than the crystalline melting point of polypropylene of the powder and not higher than the crystalline melting point + 110 ° C. A method for producing a crystalline polypropylene sheet for differential pressure forming, which comprises continuously transferring by constriction with one or a plurality of pairs of rotating rolls having a surface temperature set in a range of temperature and shaping into a sheet.