JPS5887024A - Polypropylene stretched film - Google Patents

Abstract

PURPOSE:To obtain the titled film that is excellent in optical properties such as see-through and transparency, can be stretched favorably, and produces fumes less and smears rolls less when it is calendered, by incorporating a specific quantity of a sorbitol derivative that can serve as a crystallizing nucleator into a crystalline polypropylene. CONSTITUTION:100pts.wt. crystalline polypropylene (preferably a crystalline propylene monopolymer of an isotactic polymer and/or a copolymer of propylene with another alpha-olefin that has a melt index of 1-4) and 0.05-1.0pts.wt. sorbitol derivative[preferably dibenzylidenesorbitol, 1.3, 2.4-di(methylbenzylidene) sorbitol]that can serve as a crystallizing nucleator are mixed, and the mixture is melted and calendered preferably at 200-300 deg.C, and is stretched at 120-160 deg.C so that the aimed film whose diffused transmission light intensity is 6% or below and haze is 1% or below is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a stretched polypropylene film with excellent optical properties.

Polypropylene is an excellent synthetic resin with high rigidity and mechanical strength, but its dimensional properties are greatly improved by -axial or biaxial stretching, and its optical properties,
Since it also has improved cold resistance, it is widely used in various packaging applications after being stretched and made into biaxially stretched films.

However, depending on the application, these properties are not fully satisfied; for example, good optical properties such as transparency and transparency are highly required, and in some packaging fields, the performance is insufficient. Its use is restricted as such.

For these reasons, attempts have been made to improve the optical properties of polypropylene stretched films. As a method, Tokko Sho & A-/, No. 279, Tokko Sho 3;'l
-/, No. F779, etc., disclose that a biaxially stretched film containing a specific alicyclic hydrocarbon resin or terpene polymer is improved in optical properties such as transparency and gloss. There is. However, the biaxially stretched film obtained by this method has insufficient improvement in optical properties, and furthermore, because it contains a considerable amount of compounding agents such as alicyclic hydrocarbon resin, the solvent resistance inherent in polypropylene is impaired. There are problems such as damage, smoke generation during film formation, and heavy roll stains.

The inventors of the present invention conducted extensive studies in view of these drawbacks, and as a result,
By melt-forming a composition containing crystalline polypropylene and a small amount of a sorbitol derivative that can act as a crystallization nucleating agent and then stretching it, transparency and It was discovered that a stretched film with excellent optical properties such as transparency can be obtained, leading to the present invention. That is, the present invention consists of a composition in which a θ weight part of a sorbitol derivative that can act as a crystallization nucleating agent is blended with a θ weight part of crystalline polypropylene/θ θ weight part, and the diffuse transmitted light intensity is lower than that of Otsuchi. The polypropylene stretched film is characterized in that the haze is lower than The composition within the scope of the present invention generates less smoke and roll stains during melt film formation, and also has good stretching processability.

An example of blending a crystallization nucleating agent as a modifier for polypropylene is in Tokko Sho 3? -/Gu θ Suzu No. Publication, Special Publication 32-. 5?
No. 33, JP-A No. 37-2279θ, etc., but these only describe the effects when applied to extrusion molded products and melt-formed films; It doesn't suggest anything.
Nor can the facts revealed by the present invention be inferred from these inventions. In other words, Japanese Patent Publication No. 39/1989 discloses that crystalline polymers and copolymers made of α-monoolefins are mixed with a metal salt of a specific carboxylic acid, and then rapidly cooled from the molten state to crystallize. This is a method for producing a mixture characterized by ``The mixture or product of the invention contains only a very large number of but only very small spherical states...'' As is clear from the description of □, it is possible to improve transparency by generating a fine spherulite state during crystallization. On the other hand, stretched film goes through the process of melt-forming, but is then produced by stretching at a temperature of below the melting point of polypropylene to above /θθ°C, usually at a magnification of 3 times or more. This is accompanied by significant changes in crystal structure, etc. from the original fabric stage formed as a film. Therefore, the properties of the stretched film cannot be estimated simply from the properties at the original film stage. We tried manufacturing fabrics and stretched films, but found that while we were able to obtain good transparency at the raw fabric stage, stretched films without the addition of carboxylic acid metal salts had better transparency. The results were good.0 Also, when the above mixture was used, there were many membrane breaks during stretching.Next, Japanese Patent Publication Sho-Midzu No. 235, JP-A Sho J/-, 2λ71
1theta car. describes a method for manufacturing and modifying a composition in which a sorbitol derivative is blended with polypropylene in a range of θ, θ/~, and t%, but in this case also, the above-mentioned Japanese Patent Publication No. 3? - As in the case of Publication No. 7906, No. 2, the film was melt-formed over the extruded product. Application to stretched films, which is the object of the invention, is not suggested at all.

It was completely unexpected that a stretched film with good visibility and transparency could be produced by incorporating a small amount of a monomer derivative.

The crystalline polypropylene is a crystalline propylene homopolymer consisting of an isotactic polymer or a copolymer of propylene as a main component or a copolymer of propylene and other α-olefin, but it may also be a mixture of the two.

Further, the melt index of the crystalline polypropylene is not particularly limited, but in the current processing technology, from the viewpoint of melt film forming processability or stretching processability, θ. The range from J to O is good 1
Especially preferably, the range is from / to .

Sorbitol derivatives that can act as crystallization nucleating agents used in the present invention include dibenzylidene sorbitol, /.3, . 2-gauge (alkyl'benzylidene) sorbitol, /3
9.2 Gauge (alkoxyhenzylidene) sorbitol is an example, but any substance that can act as a crystallization nucleating agent for polypropylene and can be uniformly dispersed during blending or melt film formation. There are no particular limitations. A particularly preferred sorbitol derivative is dibenzylidene sorbitol 3.2 gauge (methylbenzylidene) sorbitol.

In the above-mentioned exemplified compounds, there is no problem in including a small amount of mono(d-substituted or tri-substituted) products such as tribenzylidene rubitol and monobenzylidene sorbitol in the di-substituted product such as dibenzylidene sorbitol.

The blending amount of the sorbitol derivative that acts as a crystallization nucleating agent and obtains 2 is θ with respect to the crystalline propylene polymer/θθ
. The range is 65 to 7.0 parts by weight, and θ. If it is less than 1 part by 6 parts, the effect of improving visibility and transparency will be insufficient, and if it exceeds 6 part by weight, problems such as adhesion to the film will occur, making it impossible to put it to practical use.

The preferred range for the blending amount is θ, /~θ. 5 parts by weight.

There are no particular limitations on the melt film forming method and stretching method, but melt film forming is preferably carried out at a temperature of 100°C to 3θθ°C, and stretching is preferably carried out at a temperature of 7.20°C to 3θθ°C.
It is preferable to carry out the process at a temperature within the range of °C. The method for producing the composition to achieve the object of the present invention is any method that can substantially uniformly disperse the sorbitol derivative, which is a crystallization nucleating agent, in crystalline polypropylene. Any method may be used, but examples include a method in which both are tri-blended using a Henschel mixer or the like, or further melt-kneaded, or directly melt-kneaded without tri-blending. In addition to the sorbitol derivative as a crystallization nucleating agent, this composition can optionally contain anti-deterioration agents, lubricants, antistatic agents, etc. that are commonly added to polypropylene (7).

Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto. In the Examples, etc., the melt index, diffuse transmitted light intensity, and haze were measured according to the following methods. be.

(1) Melt index A mixture of polypropylene powder with 7 wt % of BITo and 3 wt % of calcium distearate was measured in accordance with KA''B;g from J.

(,2) Diffuse transmitted light intensity (T, S II) The 0LSI value measured by Toyo Seiki Co., Ltd.'s LSI tester (receives scattered transmitted light at an angle of 7.2° to 3.6°) is the transparency observed with the naked eye. It was used as a measure of transparency because it corresponds fairly well with

The larger the LSI value, the lower the transparency.

(3) Haze Measured according to ASTM D/θ03.

(Za) Example/Comparative Example/~2 Melt Index Co, θ crystalline polypropylene/θ
For θtt part, dibenzylidene sorbitol 05.
2 parts by weight, BITo as a stabilizer, 2 parts by weight, calcium stearate θ. After adding 7 parts by weight and mixing with a Henschel mixer, pellets were made by a conventional method using an extruder. This pellet was melted and pressurized using a hot press molding machine set at 2λθ℃, and then 30℃
A sheet having a thickness of 3θθμ was obtained by cooling with a cooling press in which water was circulated. This sheet was stretched 9 times in the machine direction and 9 times in the transverse direction while heating at 73θ°C to obtain a biaxially stretched film having a thickness of about 2θμ. Similar experiments were repeated three times, and good drawn products were obtained in each case. The characteristic values of the obtained stretched film are shown in Table 1, and it was found that LSI=/% haze-o, q%, and both visibility and transparency were good.

No dibenzylidene sorbitol was added for comparison.
Similar experiments were conducted on a system in which 80.2 parts by weight of aluminum salt of P-tert-butylbenzoic acid was added in place of dibenzylidene sorbitol. The characteristic values of the obtained stretched film are shown in Table 1.

Table 2 shows the stretchability and characteristic values of the stretched film when the amount of crystallization nucleating agent was changed under the same conditions as in the practical example.

The pellets of Example/and Comparative Example/ were melt-extruded at 27θ°C using a 6JAyuφT die extruder, and then
．． It was rapidly cooled with a cooling roll at 5° C. to obtain a sheet having a thickness of /Ill. This sheet was stretched by a factor of 5 in the machine direction while heating at 0°C, then 5 times in the transverse direction while being heated with hot air at 760°C, and then subjected to tension heat treatment at 15θ°C for S seconds to reduce the thickness. A biaxially stretched film of approximately 5θμ was obtained.

The characteristic values of this stretched film are shown in Table 3.

Example G S Comparative Example G Pellets were made under the same conditions as in Example/with varying amounts of crystallization nucleating agents. The pellets were melt-extruded at 27θ°C using a qθAyuφT die extruder, and then extruded at 33°C.
A sheet having a thickness of 3θθμ was obtained by quenching with a cooling roll.

This sheet was stretched in the same manner as in Examples to obtain a biaxially stretched film with a thickness of approximately 2θμ. The observation results of smoke generation and roll staining during melt extrusion 2 and the characteristic values of the stretched film were as shown in Table 9.

Table

Claims (1)

[Claims] Sorbitol derivative θ capable of acting as a crystallization nucleating agent for 12709 parts by weight of crystalline polypropylene. 1. A polypropylene stretched film comprising a composition containing 05 to 8 θ parts by weight, and having a diffused transmitted light intensity lower than 6 and a haze lower than /H.