JP2955325B2 - Biaxially oriented polypropylene film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a biaxially oriented polypropylene film having excellent dimensional stability at high temperatures and excellent antistatic properties, and in particular, packaging materials for printing and the like. The present invention relates to a biaxially stretched polypropylene film useful as a film.

[Conventional technology]

Hitherto, biaxially stretched polypropylene films have been widely used as packaging materials and the like, taking advantage of their excellent mechanical strength, transparency, moisture resistance, and the like.

However, biaxially oriented polypropylene films are
It has the drawback of poor dimensional stability at high temperatures, such as problems such as shrinkage of the film during heating and drying in secondary processing such as printing and coating, causing multicolor printing to wear out, or deteriorating the appearance. May cause. And
As a method of improving the dimensional stability at this high temperature,
It is known to use polypropylene having a high isotactic index as a measure of crystallinity.

In addition, biaxially stretched polypropylene film is easily charged by friction and the like, like a general plastic film, which causes adverse effects such as dust adhering to the film surface and poor riding of printing ink or surface coating agent. Is causing. As an antistatic method, the incorporation of an antistatic agent into the film itself is effective from the viewpoint of its durability, and has been conventionally employed.

[Problems to be solved by the invention]

In order to improve dimensional stability at high temperatures, biaxially oriented polypropylene films manufactured using polypropylene with a high isotactic index have difficulty transferring the antistatic agent contained in the film itself from the inside of the film to the surface. Becomes, the antistatic effect is not sufficiently exhibited, while, in order to sufficiently exhibit the antistatic effect,
If the isotactic index of polypropylene is reduced, a decrease in dimensional stability at high temperatures cannot be avoided.

The present inventors have conducted various studies on compatibility between dimensional stability at high temperature and antistatic properties of a biaxially oriented polypropylene film, and as a result, the respective densities of the raw polypropylene and the biaxially oriented polypropylene film are dominant for achieving these properties. It has been found that the present invention is a strategic factor, and the present invention has been completed.

Accordingly, an object of the present invention is to provide a biaxially oriented polypropylene film having excellent dimensional stability at high temperatures and excellent antistatic properties.

[Means for solving the problem]

The biaxially stretched polypropylene film of the present invention is a biaxially stretched film molded from polypropylene having a density of 0.9070 g / cm ³ or less, which is described in detail below, and the film has a density of 0.9100 g / cm ³ or more. With 0.1% antistatic agent
1.51.5% by weight.

Examples of the polypropylene in the present invention include a homopolymer of propylene, a copolymer of propylene with an α-olefin such as ethylene and butene-1, and a mixture thereof. Α- other than propylene in the case of a copolymer
The olefin content is preferably at most 5% by weight.

The biaxially oriented polypropylene film of the present invention has a density of
It is molded from polypropylene of 0.9070 g / cm ³ or less, preferably 0.9035 to 0.9067 g / cm ³ , and more preferably 0.9040 to 0.9036 g / cm ³ . If the density exceeds 0.9070 g / cm ³ , the antistatic effect of the contained antistatic agent described later will not be sufficiently exhibited as a biaxially stretched polypropylene film.

The melt flow rate (MFR) of this polypropylene at 230 ° C. and a load of 2.16 kg is usually 0.5 to 10 g / 10 minutes,
Preferably 1.5 to 8 g / 10 minutes, more preferably 2 to 7 g / 10
Min and the ratio of the weight average molecular weight M _W to the number average molecular weight M _N, the M _W / M _N, usually 3-30, preferably 4-20, more preferably 5-15.

Furthermore, biaxially oriented polypropylene film of the present invention has a density of 0.9100g / cm ³ or more, preferably 0.9107 to 0.917
0 g / cm ^3, with still more preferably 0.9115~0.9150g / cm ^3, and an antistatic agent containing 0.1 to 1.5 wt%. If the density of the film is less than 0.9100 g / cm ³ , the dimensional stability at high temperatures will be poor. Specifically, the value of 3% or less in the longitudinal shrinkage at 135 ° C., which is allowable in multicolor printing, cannot be achieved. The content of antistatic agent is 0.1% by weight.
If the amount is less than 1.5%, the antistatic property is inferior. If the amount exceeds 1.5% by weight, the surface becomes tacky and a problem of blocking property occurs.

As the antistatic agent in the present invention, those generally used as an antistatic agent for plastics may be used, and specifically, nonionic surfactants (for example, fatty acid esters of polyhydric alcohols, ethylene oxide of alkylamines) Adducts, fatty acid esters of alkylamine ethylene oxide adducts, etc.), anionic surfactants (eg, alkylbenzene sulfonates, higher alcohol sulfates, etc.), and cationic surfactants (eg, aliphatic amine salts) And quaternary ammonium salts), and amphoteric surfactants (eg, imidazoline type, betaine type, etc.). Among them, fatty acid esters of polyhydric alcohols, ethylene oxide adducts of alkylamines, and fatty acid esters thereof, And betaine-type amphoteric surfactants and the like are preferable.

Further, the biaxially oriented polypropylene film of the present invention contains, if necessary, an antioxidant, a heat stabilizer, a lubricant, an antiblocking agent, an ultraviolet absorber, a pigment and the like within a range not to impair the effects of the present invention. May be.

The biaxially-stretched polypropylene film of the present invention can be produced by a stretching method usually performed industrially, i.e., simultaneous biaxial stretching, sequential biaxial stretching, etc., among others, those produced by sequential biaxial stretching. Preferably it is.
Stretching is usually 2 to 10 times, preferably 4 to 6 times in the machine direction,
The film is preferably stretched usually 5 to 15 times, preferably 8 to 12 times in the transverse direction.

The thickness of the film is not particularly limited, but is usually from 8 to
100μ, preferably 10-60μ is good.

Further, the film of the present invention has a surface having a wetting tension of preferably 40 dyn / cm or more, more preferably 42 dyn / cm or more.
It is preferable that the substrate be subjected to a corona discharge treatment so as to have a dyn / cm or more.

[Action and effect]

Since the biaxially stretched polypropylene film of the present invention has a density of a specific value or more, it has excellent dimensional stability at high temperatures, and is formed from polypropylene having a density of a specific value or less, and Since the antistatic agent is contained in an amount, the antistatic property is also excellent.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

The evaluation method used in the examples and comparative examples is the following method.

(1) Density of Raw Polypropylene Raw polypropylene pellets were press-molded at 230 ° C. under a load of 150 kg to form a 2 mm heat sheet. 105 this sheet
After heat treatment at 90 ° C. for 90 minutes, the density was measured with a density gradient tube according to ASTM D1505.

(2) Density of Film The density of the biaxially stretched polypropylene film was measured with a density gradient tube according to ASTM D1505.

(3) Heat shrinkage The biaxially stretched polypropylene film is cut into a width of 30 mm and a length of 300 mm in the longitudinal direction (the direction of film flow) and the transverse direction (the direction perpendicular to the direction of film flow), and 135
The length after the heat treatment in an oven at 15 ° C. for 15 minutes was measured and determined according to the following equation.

However, L ₁ : length before heat treatment L ₂ : length after heat treatment (4) Antistatic properties For biaxially oriented polypropylene film aged at 40 ° C for 2 days after molding, constant temperature and humidity of 23 ° C and 50% RH In the room, a static honest meter (TY) manufactured by Shishido Shokai Co., Ltd.
PES-5109).

(5) MFR According to ASTM D1238-1986, MFR was measured at 230 ° C. under a load of 2.16 kg.

Examples 1 to 4, the density as shown in Comparative Example 1 in Table 1, MFR, and M in propylene homopolymer 100 parts by weight with _W / M _N, glyceryl monostearate 0.5 parts by weight, and alkylamine derivative-based surfactant 0.5 part by weight of the compounding agent, melt-kneaded with an extruder and pelletized.
The sheet was melt-extruded at 0 ° C and quenched with a cooling roll at 20 ° C to form a sheet. Next, the sheet is stretched 5 times in the machine direction at a stretching temperature of 128 ° C. between rolls, and subsequently stretched 10 times in the transverse direction at a stretching temperature of 166 ° C. with a tenter stretching machine, whereby a biaxially stretched polypropylene film having a thickness of 30 μm Was subjected to corona discharge treatment so that the wet tension of the film surface became 42 dyn / cm.

The density, antistatic property, and heat shrinkage of the obtained film were evaluated, and the results are shown in Table 1.

Comparative Examples 2 and 3 A biaxially oriented polypropylene film was produced in the same manner as in Examples 1 to 4 and Comparative Example 1, except that the film was stretched 5 times in the machine direction at 132 ° C and 10 times in the transverse direction at 170 ° C. did.

Example 5 Examples 1 to 10 except that the stretching ratio in the machine direction was 4.5 times
4. A biaxially stretched polypropylene film was produced in the same manner as in Comparative Example 1.

Example 6 A biaxially stretched polypropylene film was produced in the same manner as in Examples 1 to 4 and Comparative Example 1, except that glyceryl monostearate was 0.2 parts by weight and an alkylamine derivative-based surfactant was 0.2 parts by weight. .

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C08J 5/18 B29C 55/12-55/16 C08L 23/12

Claims (1)

(57) [Claims] 1. A biaxially stretched film formed from polypropylene having a density of 0.9070 g / cm ³ or less, wherein the film has a density of 0.9100 g / cm ³ or more and has an antistatic agent.
A biaxially oriented polypropylene film characterized by containing 0.1 to 1.5% by weight.