JPH08291233A - Polypropylene resin composition for drawn film - Google Patents

Abstract

PURPOSE: To obtain a PP resin composition for a drawn film having excellent blocking resistance, transparency and scratch resistance and useful as a packaging film, etc., by compounding a PP resin with a specific crushed silica fine powder at a specific ratio. CONSTITUTION: This resin composition is produced by compounding (A) 100 pts.wt. of a PP resin with (B) 0.03-0.30 pts.wt. of a crushed silica fine powder surface-treated with a polyorganosiloxane such as a polyalkylsiloxane. The PP resin preferably has a melt flow rate of 1.0-5.0g/10min.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene resin composition for a stretched film, which is useful as a packaging film. More specifically, a polypropylene for stretched film, which is made by adding a small amount of crushed fine powder silica surface-treated with polyorganosiloxane to a polyolefin resin, and has improved blocking resistance, transparency, and scratch resistance (scratch resistance). It relates to a resin composition.

[0002]

2. Description of the Related Art Polypropylene films are used for packaging films and the like by taking advantage of their excellent transparency, rigidity and strength. However, the polypropylene film is apt to cause blocking between the films, so that workability is impaired and the film is easily damaged. Therefore, an anti-blocking agent such as silica powder is added to the polypropylene material. The addition of the anti-blocking agent improves the blocking resistance to some extent, but impairs the inherent transparency of the polypropylene film. In particular, when finely divided silica is used as the anti-blocking agent, the dispersibility is poor because of the hydroxyl groups on the silica surface or because the surface is porous, and the traces visually observed in the film remain and the transparency and The appearance is impaired, and the physical properties such as printability and laminating property are deteriorated.

For the purpose of solving such a problem, finely powdered silica to be blended with polyolefin is coated with an organic substance such as metal soap, paraffin wax or polyolefin wax to improve the dispersibility in polyolefin to form a film. It has been proposed to improve the balance of physical properties such as blocking resistance and transparency (Japanese Patent Laid-Open No. 2-55750).

However, this polyolefin film is apt to be scratched when the films are rubbed with each other (inferior in so-called "scratch resistance"), and has a transparency when uniaxially or biaxially stretched for the purpose of improving film strength. However, there are still problems such as a decrease and an unsatisfactory blocking resistance.

Accordingly, an object of the present invention is to provide a polypropylene resin composition for a stretched film which is excellent in blocking resistance and scratch resistance (scratch resistance), and whose transparency does not decrease even when stretched. is there.

[0006]

Means for Solving the Problems As a result of intensive studies by the present inventors, a composition obtained by blending a small amount of crushed fine powder silica surface-treated with polyorganosiloxane in a polypropylene resin was found to have blocking resistance and scratch resistance. The present invention has been completed based on the finding that the transparency is not deteriorated even when stretched, and the physical properties of the film are well balanced.

That is, according to the present invention, (1) 0.03 to 0.30 of crushed fine powder silica surface-treated with polyorganosiloxane is added to 100 parts by weight of polypropylene resin.
A polypropylene resin composition for a stretched film, characterized by being mixed in an amount of 1 part by weight, and (2) a polypropylene resin composition for a stretched film as described in 1 above, wherein the polyorganosiloxane is a polyalkylsiloxane. . Hereinafter, the polypropylene resin composition of the present invention will be described in detail.

[0008]

[Polypropylene Resin] The polypropylene resin used in the present invention is a homopolymer of propylene (homopolypropylene) and random polypropylene containing 2% by weight or less of an ethylene component. Its melt flow rate (MF
R, 230 ° C., 2.16 kg load) is preferably 0.5 to 10 g / 10 minutes, more preferably 1.0 to 5.0 g / 10 minutes. A random polypropylene having an ethylene content of more than 2% by weight is not preferable because the scratch resistance is deteriorated.

[0009]

[Fine powder silica] The fine powder silica used in the present invention is surface-treated with polyorganosiloxane. Examples of the raw material fine powder silica to be treated with polyorganosiloxane include fumed silica, precipitated silica, silica aerogel, and calcined silica. Among them, among these,
The shape is a crush type, and the average particle size is 1 to 10 μm, especially 2
Use a ˜6 μm one. If the average particle size is less than 1 μm, the anti-blocking effect is lowered, and if it exceeds 10 μm, the transparency is deteriorated.

In the present invention, the crushable fine powdery silica is surface-treated with polyorganosiloxane before use.
Hydroxyl groups that bond to silicon atoms are present on the surface of the crushable fine powder silica, and when polyorganosiloxane is added and baked at high temperature, some of the organic groups of polyorganosiloxane are released, and The water vapor turns into silanol groups and condenses with the hydroxyl groups on the silica surface to form a polyorganosiloxane layer on the silica surface.

Known polyorganosiloxanes include those having a chain structure such as polyalkylsiloxane, those having a cyclic structure such as octamethylcyclotrisiloxane, and those having a ladder-like structure, a cage-like structure, and a three-dimensional network structure. However, any of them can be used in the present invention. Of these, polyalkyl siloxanes that are easy to obtain and handle are preferable, and particularly, the treatment is easy,
Substantially linear polymethylsiloxane having a degree of polymerization of 10 or more, which can easily form a siloxane layer on the surface of crushable fine powder silica, is preferable. The terminal group of such a polyalkylsiloxane may be a trimethylsilyl group or a hydroxydimethylsilyl group. When the degree of polymerization is less than 10, it tends to be vaporized during the surface treatment of fine powder silica, and it is difficult to form an effective siloxane layer by baking for a short time.

The surface treatment of the crushable fine powder silica may be carried out by an ordinary method. For example, polyorganosiloxane or a solvent solution of polyorganosiloxane is added to crushed fine silica powder, and sufficiently stirred. When a solvent is used, this is removed under reduced pressure, and then heated to high temperature to bake the polyorganosiloxane on the surface of the fine silica powder. . As the solvent, hydrocarbons such as toluene, xylene, n-hexane, n-heptane and petroleum benzine, and halogenated hydrocarbons such as trichlene and 1,1,1-trichloroethane are used. The baking temperature varies depending on the type of polyorganosiloxane, but in the case of polymethylsiloxane, for example, it is a temperature at which elimination of a methyl group occurs, that is, 200 ° C. or higher,
It is preferably between 350 ° C.

The coating amount of polyorganosiloxane is 0.5 in terms of carbon content based on the finely divided silica after treatment.
The amount is 10 to 10% by weight, preferably 1 to 4% by weight. The carbon content was measured by treating the treated finely divided silica with 15
After sufficiently drying while flowing a nitrogen gas at 0 ° C., elemental analysis is performed. If the coating amount is small, the dispersibility will be poor, and if it is too large, the physical properties of silica as an antiblocking agent will be impaired, such being undesirable.

The surface-treated crushable fine powder silica can be blended with the polypropylene resin by melt-kneading. Melt kneading can be carried out by various conventionally known methods such as using a batch type kneader such as a Banbury mixer, a Brabender, a kneading roll or the like, or a continuous kneader such as a single screw extruder or a twin screw extruder. Kneading is 18
It can be carried out at a temperature of 0 to 260 ° C. The surface-treated crushed fine silica powder may be dry-blended with polypropylene in advance, or, when kneading is performed by an extruder or the like, it is fed from the middle of the extruder using a gravimetric feeder or the like. You may.

The blending amount of the surface-treated fine powder silica is
0.03 to 0.3 per 100 parts by weight of polypropylene resin
0 parts by weight. If the amount of finely divided silica is less than 0.03 parts by weight, the blocking resistance is lowered, and if it exceeds 0.30 parts by weight, the transparency is lowered.

Further, in the present invention, in addition to the above components,
Additives optionally used in the field of molding resin compositions, for example, inorganic fillers, ultraviolet absorbers, processing aids,
A heat stabilizer, a light stabilizer, a flame retardant, an antistatic agent, a nucleating agent and the like can be appropriately added, and these are added within a range that does not impair the effect of the film of the present invention.

The polypropylene resin composition for stretched film of the present invention obtained as described above can be subjected to film forming and stretching treatment by a conventionally known method. The film molding may be carried out by any molding method such as an extrusion molding method, a press molding method, a calender molding method, a tenter method and an inflation molding method, but when the film is uniaxially or biaxially stretched, molding by a tenter method is preferable. preferable.

When biaxial stretching is carried out by the tenter method, there are successive biaxial stretching and simultaneous biaxial stretching as the stretching methods.
Either method may be used. For example, in successive biaxial stretching, the roll temperature difference of 90 is used in the machine direction (MD) direction by utilizing the peripheral speed difference of the roll.
~ 160 ° C, preferably 3 to 8 times at 105 to 150 ° C,
Preferably, the film is stretched 4 to 6 times, and then the film is held by a clip or the like, and stretched in the tenter oven at 150 to 170 ° C. 3 to 12 times, preferably 6 to 11 times in the transverse (TD) direction. If the stretching temperature exceeds the above range, the film is likely to be broken, or the stretching cannot be sufficiently performed, and the effect of stretching cannot be obtained.

[0019]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples. The following materials were used as raw materials and additives in each example and comparative example.

Polypropylene resin (1) Homo polypropylene (Homo PP): MFR (230
℃, 2.16kg load) 2.8g / 10 minutes. (2) Propylene-ethylene random copolymer (random PP): ethylene content 0.4% by weight, MFR (230 ° C,
2.16kg load) 2.5g / 10 minutes.

Surface-treated crushable fine powder silica (3) Si-1: crushed silica having an average particle diameter of 2.8 μm, coated with polymethylsiloxane in a carbon content of 3% by weight. (4) Si-2: A surface of crushed silica having an average particle diameter of 5.0 μm, coated with polymethylsiloxane in a carbon content of 3% by weight. (5) Si-3: A surface of crushed silica having an average particle diameter of 4.6 μm, coated with polyethylene wax in a carbon content of 3% by weight. Untreated silica (6) Si-4: crushed silica having an average particle size of 2.4 μm. (7) Si-5: Spherical silica having an average particle size of 2.8 μm.

Examples 1 to 5 and Comparative Examples 1 to 5 The components were mixed in the proportions shown in Tables 1 and 2 (numerical values in the tables are parts by weight) and kneaded at a kneading temperature of 220 ° C. with a single screw extruder. Then, pellets of the polypropylene resin composition for stretched film were obtained. The pellets were extruded at 250 ° C. using a 75 mmφ extruder and a single layer die to obtain a sheet. This sheet is TD at a temperature of 140 ° C five times in the MD direction.
The film was stretched 8 times in the direction to obtain a polypropylene film having a thickness of 20 μm. With respect to these films, transparency (haze), blocking resistance and scratch resistance (scratch resistance) were measured and evaluated. The results are shown in Table 1 and Table 2.
Are also shown.

The physical properties were measured by the following methods. (1) Transparency (haze): Measured according to JIS K 7105. (2) Blocking resistance: polypropylene film (width 2
0cm x length 30cm x thickness 20μm) 2 pieces are piled up to make the overlapping area 40cm ² and 2kg
After the load was applied and held at 50 ° C. for 24 hours, the force (g / cm ² ) required to peel off the two films was measured. (3) Scratch resistance (scratch resistance): Polypropylene film (width 20 cm x length 30 cm x thickness 20 μm) 2
Stack the sheets, and make the overlapping area 40cm ² .
Lower film is fixed, ² per 40 cm ^{2 of} upper film
Applying a load of kg, the upper film is reciprocally moved 2 times in the horizontal direction, and the transparency (haze) of the film after the rubbing is performed.
It was measured according to JIS K 7105.

[0024]

[Table 1] Example No. 1 2 3 4 5 (1) Homo PP 100 100 100 100 (2) Random PP − − − − 100 (3) Si-1 0.05 0.10 0.20 − 0.10 (4) Si−2 − − − 0.10 − ( 5) Si-3 − − − − − (6) Si-4- − − − − − (7) Si-5 − − − − − (1) Transparency (%) 1.6 1.9 2.3 2.3 1.7 (2) Blocking resistance Resistance (g / cm ² ) 35 26 15 20 30 (3) Scratch resistance (%) 3.1 3.5 4.3 4.5 4.0

[0025]

[Table 2] Comparative example number 1 2 3 4 5 (1) Homo PP 100 100 100 100 100 (2) Random PP − − − − − (3) Si-1 − − − 0.01 0.5 (4) Si-2- − − − − − (5) Si-3 0.10 − − − − (6) Si-4-0.10 − − − (7) Si-5 − − 0.10 − − (1) Transparency (%) 3.4 4.0 2.0 0.7 5.8 (2) Resistance Blocking property (g / cm ² ) 32 28 25 83 <5 ^* (3) Scratch resistance (%) 5.5 6.0 12.8 1.0 14.9 *: Less than the lower limit of measurement

As is clear from Tables 1 and 2, the film moldings containing untreated silica (Comparative Examples 2 to 3) have good blocking resistance, but have a crushable shape (Comparative Example 2). ) Has low transparency and insufficient scratch resistance (scratch resistance), and has a spherical shape (Comparative Example 3).
Has good transparency, but scratch resistance is significantly reduced. Further, when the fine powder silica treated with polyethylene wax is blended (Comparative Example 1), neither transparency nor scratch resistance is satisfactory. Against these,
The film moldings (Examples 1 to 5) obtained from the resin composition of the present invention in which a specific amount of crushable silica surface-treated with polyorganosiloxane is blended have good transparency, blocking resistance and scratch resistance. It can be seen that it has an excellent balance of physical properties. When the compounding amount of the polyorganosiloxane-treated silica is out of the specified range, there is a problem in the balance of physical properties. That is, when the blending amount is small (Comparative Example 4), the transparency and scratch resistance are good, but the blocking resistance is lowered, and when the blending amount is large (Comparative Example 5), the blocking resistance is good. Although good, transparency and scratch resistance are reduced.

[0027]

The polypropylene resin composition for a stretched film of the present invention comprises polypropylene resin and crushed fine powder silica surface-treated with polyorganosiloxane, and when formed into a film, has blocking resistance and transparency. It has excellent characteristics and scratch resistance (scratch resistance), and has the characteristics that transparency does not decrease even when stretched, and is useful as various packaging films.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location // B29K 23:00 B29L 7:00

Claims (2)

[Claims] 1. A polypropylene resin composition for a stretched film, comprising 0.03 to 0.30 parts by weight of finely divided pulverized silica surface-treated with polyorganosiloxane, based on 100 parts by weight of the polypropylene resin. 2. The polypropylene resin composition for a stretched film according to claim 1, wherein the polyorganosiloxane is a polyalkylsiloxane.