JPH0126859B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polypropylene sheet and a method for manufacturing the same. Conventionally, polypropylene sheets have excellent strength, heat resistance, moisture permeability, etc., and are therefore formed by thermoforming means such as vacuum forming and pressure forming and used as various lightweight containers. However, polypropylene sheets obtained by conventional molding methods are inferior to polystyrene, polyvinyl chloride resin, etc. in terms of transparency, rigidity, thermoformability, etc., and therefore their use is severely limited. In particular, its transparency is even lower and it has not reached the point where it can replace competing products. Therefore, in order to improve the transparency of polypropylene, various proposals have been made to control the crystal structure by melt-extruding polypropylene and rapidly cooling the film-like body. However, in the method using a cooling roll, water droplets adhere to the roll surface, so
Unable to cool below dew point. For this reason, there are limits to the quenching conditions, and sheets with excellent surface conditions cannot be obtained due to air entrainment. Furthermore, although the water cooling method has a high rapid cooling effect, uniform cooling is not possible, so it is difficult to obtain a sheet with excellent uniformity (on the surface and inside). Furthermore, it is known to use a nucleating agent to control the crystal structure, but the haze level is limited to 15%. For this reason,
These film forming methods have not yielded polypropylene sheets that have a haze of 7% or less and can compete with polyvinyl chloride resins. Therefore, research is focused on ways to modify the raw materials themselves by adding petroleum resins or nucleating agents, and to improve the transparency of thermoformed containers rather than the transparency of polypropylene sheets themselves. However, the addition of petroleum resin reduces the heat resistance and moisture permeability of polypropylene, and the effect of improving transparency is not sufficient. Additionally, the addition of a nucleating agent poses problems such as bleeding and hygiene issues. Therefore, in order to make a sheet with excellent transparency, the polypropylene sheet should be further
It is necessary to roll at a temperature of 125° C. and a rolling ratio of 1.5 to 3.0, which substantially causes the sheet to be oriented. The latter method involves stretching or rolling a sheet with insufficient transparency to improve its transparency to some extent, and then pressure-forming it at a relatively low temperature that causes a high degree of orientation. The container must have a haze of 10% or less. Therefore, this method cannot be used for the sheet itself, which requires transparency. Furthermore, since the sheet is oriented and furthermore, it is molded at a relatively low temperature, a special thermoforming device for high pressure is required, and the moldability is also insufficient, resulting in poor mold reproducibility. Furthermore, although the container is transparent, it is highly oriented and therefore shrinks and deforms when used at high temperatures. An object of the present invention is to eliminate the above-mentioned conventional drawbacks, and to provide a polypropylene sheet that is substantially non-oriented, has the same transparency as polyvinyl chloride, and has excellent rigidity, gloss, etc., and a method for producing the same. It is something to do. That is, the present invention first has a second endothermic peak on the lower temperature side than the melting peak, has a spherulite radius of 8.0μ or less, a haze of 7% or less, and does not have a nucleating agent with a thickness of 100μ or more. A substantially non-oriented polypropylene sheet is provided. Furthermore, the second aspect of the present invention is to melt and extrude crystalline polypropylene into a film under conditions such that the die exit temperature is 10 to 60 degrees Celsius higher than the resin temperature, and then -10 degrees Celsius.
Cooling water at a temperature of ~+50°C is introduced into an open bottom slit and rapidly cooled, resulting in an external haze of 5%.
The following sheets are heat treated at a temperature of 70°C or higher and lower than the melting point of polypropylene,
Production of a substantially non-oriented polypropylene sheet having a second endothermic peak on the lower temperature side than the melting peak, having a spherulite radius of 8.0μ or less, haze of 7% or less, and having a thickness of 100μ or more without a nucleating agent. The present invention provides a method. The first polypropylene sheet of the present invention is substantially non-oriented and has a second endothermic peak on the lower temperature side than the melting peak. Also, the spherulite radius
The haze is 8.0μ or less, and the haze is 7% or less, preferably 5% or less. Furthermore, the thickness is 100μ or more, usually 150μ ~
It is 1500μ. Moreover, the first polypropylene sheet of the present invention does not contain a nucleating agent, and is characterized in that it has excellent transparency and the like without using a nucleating agent. Therefore, there are no problems such as bleeding due to the addition of a nucleating agent or problems with hygiene. Further, the first polypropylene sheet of the present invention has a surface gloss of 100% or more, preferably 120% or less, and a tensile modulus of 15,000 Kg/cm ² or more, preferably 17,000 Kg/cm ² or more. The second aspect of the present invention provides a preferred method for producing the first polypropylene sheet of the present invention.
It is. In the second aspect of the present invention, crystalline polypropylene is used as a raw material. Examples of the crystalline polypropylene include crystalline propylene homopolymers as well as random polypropylene containing 15% by weight or less of α-olefins such as ethylene, butene-1, pentene-1, and the like. Further, the melt index (MI) of this crystalline polypropylene is 0.5 to 20 g/10 minutes, preferably 1 to 15 g/10 minutes. If the MI is less than 0.5/10 minutes, the discharge rate from the extruder will decrease, resulting in poor productivity and the resulting sheet will have low rigidity, which is not preferable. Moreover, if the MI exceeds 20 g/10 minutes, it becomes difficult to form a sheet due to the low viscosity. Furthermore, a petroleum resin or the like may be appropriately added if necessary. The petroleum resin may be either alicyclic or aliphatic, and usually has a number average molecular weight of 500 to 1000 and a softening point of 50 to 180°C. The effect of adding these petroleum resins differs in that the crystal structure of polypropylene is usually an α to β structure, but a smectica structure is obtained. Furthermore, stabilizers such as heat stabilizers and ultraviolet absorbers, antistatic agents such as various surfactants, etc. can also be added. The raw material resin is melt-extruded into a film. Here, the raw material resins homopolypropylene and random polypropylene may be coextruded in multiple layers, or the raw material resins crystalline polypropylene and modified polyolefin may be coextruded in multiple layers. As a method for melt extrusion, a T-die method or the like can usually be applied. In this way, a highly transparent molten resin film is extruded from the die outlet. In order to obtain a molten resin film with excellent transparency, it is necessary to extrude the film under conditions that make the surface of the film as smooth as possible. Specifically, the resin temperature is lowered,
Heat the die exit temperature using a die lip heater or the like to keep it relatively high. Normally, it is sufficient to provide a difference of about 10 to 60°C between the resin temperature and the die exit temperature. Furthermore, it is also effective to use a die with no scratches on its surface. Next, the extruded molten resin film is rapidly cooled.
It is necessary to control the cooling conditions in order to reduce the external haze to 5% or less by this rapid cooling. Here, the quenching temperature is
The temperature is 100°C or lower, preferably 60°C or lower. Rapid cooling is
This is carried out by introducing the molten resin film into a bottom-open slit through which cooling water at a temperature of -10°C to +50°C flows. In particular, a method of rapidly cooling the material by introducing it into a multistage slit through which cooling water flows is preferable in order to obtain a sheet with good transparency by high-speed molding. In addition, in order to rapidly cool the extruded transparent molten resin film by introducing it into a slit through which cooling water flows,
Cooling water may be made to flow through the slit, and the molten film may be introduced into the slit in the direction of water flow to rapidly cool it. The material of the slit portion is not particularly limited and may include metal, plastic, wood, cloth, etc. Further, the slit portion may be constructed of a pair of endless belts or a pair of rolls kept at a predetermined interval. In particular, by forming the slit portion in two or more stages, it is possible to obtain an excellent product with even higher productivity. The width of the slit is not particularly limited, but is usually 20 mm or less, preferably 10 mm or less, and more preferably 6 mm or less. Further, the slit height is 3 mm or more, preferably 5 mm or more. Further, as the cooling water, only water or an aqueous solution of water with an organic or inorganic thickener added thereto can be used, but an aqueous solution with a thickener added is preferable in terms of uniform cooling and surface smoothness. Here, various kinds of organic thickeners can be used, such as natural polymer substances, semi-synthetic products, and synthetic products. Natural polymer substances include sweet starch, potato starch,
Starches such as wheat starch; mannans such as konjac; seaweeds such as agar and sodium alginate; vegetable mucilages such as gum tragacanth and gum arabic; microbial mucilages such as dextran and levan; glue, gelatin, casein, collagen, etc. There are many proteins, etc. Semi-synthetic products include cellulose-based substances such as viscose, methylcellulose, and carboxymethylcellulose; starch-based substances such as soluble starch, carboxymethyl starch, and dialdehyde starch. In addition, synthetic products include polyvinyl alcohol, sodium polyacrylate, polyethylene oxide, and the like. On the other hand, inorganic thickeners include silica sol, alumina sol, clay, water glass, and various metal salts. In addition to aqueous solutions prepared by adding these thickeners to water, viscous substances such as polyethylene glycol, polypropylene glycol, and silicone oil can also be used alone. The viscosity of the aqueous solution with added thickener should be between 2 and 3000 centipoise (cp), preferably between 3 and 1000 cp. In addition, the temperature of the cooling water should be -10℃ to +50℃, and especially when manufacturing sheets with a thickness of 200μ or more, it is recommended to keep the liquid temperature below 20℃, especially preferably below 10%, to prevent haze spots from occurring. Effective. In this way, a polypropylene sheet is produced by rapidly cooling the molten resin film to usually 100°C or lower, preferably 60°C or lower. In the present invention, as described above, since the die exit temperature is set slightly higher than the resin temperature, the surface condition of the extruded molten resin film can be maintained in an extremely good condition. By rapidly cooling this film-like body, a polypropylene sheet having an external haze of 5% or less can be obtained. As described above, a polypropylene sheet having an external haze of 5% or less, preferably 4% or less is produced.
Further, the total haze (total of external haze and internal haze) of this sheet is preferably 20% or less. The crystal structure of the polypropylene sheet thus obtained is essentially a smectica structure, even though no additives such as petroleum resin are used. This sheet is then heat treated. Heat treatment is 70
It is carried out by heating using a heating roll, heated air, an inert liquid, etc. at a temperature of 80° C. or higher and 10° C. lower than the melting point of polypropylene. Although it is not particularly necessary, the shrinkage stress is 5Kg/cm ² during the above heat treatment or before and after the heat treatment.
The following moderate stretching or rolling may be performed. That is, the quenched transparent sheet is heated to a temperature below the melting point, preferably 5 to 70 degrees Celsius below the melting point, more preferably 5 to 50 degrees Celsius below the melting point,
Perform roll stretching or roll rolling. Here, the sheet may be heated using a roll, an oven, or the like. Note that the stretching may be performed by biaxial stretching in addition to uniaxial stretching. This moderate stretching or rolling imparts a slight orientation to the sheet, thereby further reducing the occurrence of sagging and wrinkles due to sheet heating while maintaining good thermoformability during thermoforming. The first polypropylene sheet of the present invention can be manufactured as described above. According to thermal analysis, this sheet has a second endothermic peak on the lower temperature side than the melting peak, has a spherulite radius of 8.0μ or less, and has a haze level of 7.
% or less. Moreover, this sheet does not develop transparency through conventionally known rolling or stretching, does not contain a nucleating agent, and is a substantially non-oriented sheet. Furthermore, the thickness of this sheet is over 100μ, usually 150μ~
It is 1500μ. In addition, this sheet usually has a surface gloss of 100% or more and a tensile modulus of 15000 Kg/cm ²
That's all. The polypropylene sheet obtained by the present invention has very good transparency, which is comparable to that of polyvinyl chloride resin. In addition, because of its excellent surface gloss, rigidity, and heat resistance, it can be used not only as a sheet itself, but also for stationery such as files, foldable containers, etc. through secondary processing. Furthermore, the contents of the various molded products obtained by molding this sheet can be seen through, making quality control easier and providing a sense of security to users, greatly increasing the product value. . Moreover, since the polypropylene sheet obtained by the present invention is substantially non-oriented, the molding pressure can be low and mold reproducibility is good, and there is no need to use expensive high-pressure thermoforming equipment. It has good thermoformability such as no heat. Moreover, since the container has a low degree of orientation, it has good heat resistance, and there is no risk of deformation due to orientation shrinkage even when used at high temperatures. Moreover, the polypropylene sheet obtained by the present invention has high strength and elastic modulus. Therefore, the thermoformed product obtained by thermoforming this product has high strength and elastic modulus, and is easy to manufacture, process, transport, and store, and there is little risk of deformation during these processes. Furthermore, since the polypropylene sheet obtained by the present invention does not cause whitening when folded, it is expected to find new fields of use not found in conventional polyvinyl chloride sheets or polypropylene sheets. Therefore, the polypropylene sheet obtained by the present invention can be used in the form of a sheet for various files, foldable containers, etc., and can also be thermoformed and effectively used for various packaging such as pristar packaging and retort food packaging. Next, examples of the present invention will be shown. Example 1 Homopolypropylene resin (density 0.91 g/cm ³ ,
MI2.1g/10min, melting point 165℃, manufactured by Idemitsu Petrochemical Co., Ltd.
Product name: Idemitsu Polypro F200S) using a T-die extrusion device (extruder 65mmφ, L/D=28, die width 550mm,
Die lip opening 2mm, lip heater heating die)
A transparent molten resin film was extruded by melt-kneading at a resin temperature of 240°C and a die lip temperature of 280°C.
Next, this membrane-like body was placed in a two-stage slit type water cooling device shown in Fig. 1 (first stage slit: height 50 mm, width 2.5 mm).
mm, slit upper water tank water level 5mm, cooling water temperature 5℃;
The material was introduced into a second stage slit (height 10 mm, width 5 mm, water tank water level above the slit 10 mm, cooling water temperature 5° C.) for rapid cooling and molding at a take-up speed of 20 m/min. to obtain a polypropylene sheet with a thickness of 0.25 mm. Table 1 shows the measurement results of the physical properties of the obtained sheet (before heat treatment).
The results of thermal analysis of this sheet are shown in FIG. 2a. The thermal analysis was performed using a differential scanning calorimeter (DSC) at a heating rate of 20° C./min. Next, this sheet was heat treated using four heat treatment rolls with a diameter of 300 mmφ (temperature 145°C).
A polypropylene sheet with excellent transparency was obtained.
Table 1 shows the measurement results of the physical properties of this sheet (after heat treatment). The results of thermal analysis of this sheet are shown in FIG. 2b. Example 2 In Example 1, other homopolypropylene resin (density 0.91 g/cm ³ , MI 8.5 g/cm 3 ) was used as the raw material resin.
10 minutes, melting point 170℃, manufactured by Idemitsu Petrochemical Co., Ltd., product name:
A polypropylene sheet was obtained in the same manner as in Example 1 except that Idemitsu Polypro F700N) was used. Table 1 shows the measurement results of the physical properties of this sheet before and after heat treatment. The results of thermal analysis of this sheet are shown in FIG. 3a (before heat treatment) and FIG. 3b (after heat treatment). Comparative Example 1 A polypropylene sheet was obtained in the same manner as in Example 1, except that a cooling roll (40° C.) was used instead of the two-stage slit water cooling device. Table 1 shows the measurement results of the physical properties of this sheet before and after heat treatment. In addition, the results of thermal analysis of this sheet are shown in Figure 4 a (before heat treatment) and Figure 4 b (after heat treatment).
Shown below.

[Table] Example 3 A polypropylene sheet was obtained in the same manner as in Example 1, except that the polypropylene sheet was molded at a take-up speed of 12.5 m/min to obtain a polypropylene sheet with a thickness of 0.4 mm. Table 2 shows the measurement results of the physical properties of this sheet before and after heat treatment. Example 4 A polypropylene sheet was obtained in the same manner as in Example 1, except that the polypropylene sheet was molded at a take-up speed of 8.3 m/min to obtain a polypropylene sheet with a thickness of 0.6 mm. Table 2 shows the measurement results of the physical properties of this sheet before and after heat treatment. Example 5 A polypropylene sheet was obtained in the same manner as in Example 1, except that it was molded at a take-up speed of 6.3 m/min to obtain a polypropylene sheet with a thickness of 0.8 mm. Table 2 shows the measurement results of the physical properties of this sheet before and after heat treatment.

[Table] *1 to *5: Same as Table 1

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing an example of the water cooling device used in the method of the present invention, Figure 2 is the result of thermal analysis of the polypropylene sheet obtained in Example 1, and Figure 3 is the result of thermal analysis of the polypropylene sheet obtained in Example 2. Figure 4 shows the results of thermal analysis of the polypropylene sheet obtained in Comparative Example 1. In each figure, a represents the results before heat treatment, and b represents the results after heat treatment.

Claims (1)

[Claims] 1. Has a second endothermic peak on the lower temperature side than the melting peak, has a spherulite radius of 8.0μ or less, a haze of 7% or less, and does not contain a nucleating agent with a thickness of 100μ or more Substantially non-oriented polypropylene sheet. 2. After melt-extruding crystalline polypropylene into a film under conditions such that the die exit temperature is 10 to 60 degrees Celsius higher than the resin temperature, a bottom-open type extrusion is carried out in which cooling water at a temperature of -10 degrees Celsius to +50 degrees Celsius flows. A sheet with an external haze of 5% or less that is introduced into a slit and rapidly cooled is heated to 70°C.
above, and characterized by being heat treated at a temperature below the melting point of polypropylene, having a second endothermic peak on the lower temperature side than the melting peak, and having a spherulite radius of 8.0μ
The following is a method for producing a substantially non-oriented polypropylene sheet having a haze of 7% or less and a thickness of 100 μm or more without a nucleating agent.