JPS6053064B2 - Method for producing non-whitening transparent polypropylene film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a biaxially oriented polypropylene film that can maintain good transparency without whitening over a long period of time.

Biaxially oriented polypropylene film has various excellent properties such as transparency, moisture resistance, mechanical strength, impact resistance, cold resistance, and aging resistance, so it is widely used for packaging, especially food packaging. .

This biaxially oriented polypropylene film is usually produced by a flat film method or a blown film method, but when using the flat film method, a lubricant is used to improve moldability. However, lubricants used in food packaging films are legally regulated for food hygiene reasons, and only safe lubricants that do not affect the human body are permitted. Under these circumstances, higher fatty acid monoglycerides are most often used as lubricants for polypropylene films for food packaging. This higher fatty acid monoglyceride has no problem in terms of its action as a lubricant, but when it is kneaded into polypropylene and biaxially stretched, it causes a significant blooming phenomenon, or whitening, after film formation, so it has commercial value without damaging the film surface appearance. It has the serious drawback of reducing the In addition, considering the period from when the film is formed to the product and when exporting to other countries, the anti-whitening performance period must be at least 60 days. I need it. In other words, packaging materials are required to have high transparency depending on their use, but biaxially oriented polypropylene films for food packaging have been subject to long-term restrictions due to the aforementioned additive regulations from food hygiene reasons. Excellent transparency across the board. I couldn't get anything. Until now, as a method of improving transparency over a long period of time, for example, a method of using the above-mentioned glycerin monostearate in combination with a certain amine derivative has been known (Japanese Patent Laid-Open No. 48-54155
Publication No.).

However, with this method, transparency can only be maintained for a period of 30 to 40 days at most, and the objective cannot be achieved for an extremely long period of 60 days or more. Furthermore, as a result of experiments, the present inventors confirmed that a biaxially oriented polypropylene film to which glycerin monostearate was added alone undergoes a significant whitening phenomenon within 30 days.

The present inventors have conducted intensive research to prevent whitening of biaxially oriented polypropylene films using higher fatty acid monoglycerides as lubricants and to obtain packaging materials with excellent long-term transparency. , higher fatty acid amide and higher fatty acid/metal salt 3
By adding these components, they act in a well-balanced manner on the biaxially stretched polypropylene film, suppressing excessive free-out of higher fatty acid monoglycerides,
Furthermore, the inventors have discovered that whitening can be prevented for a long period of time without impairing the processability or film properties of polypropylene, and based on this knowledge, the present invention has been completed. That is, the present invention provides a lubricant having a general formula (wherein R1 has 14 carbon atoms)
In producing a polypropylene film by biaxially stretching polypropylene containing a higher fatty acid monoglyceride represented by the formula (18 alkyl or alkenyl group), the general formula (
0.01 to 0.5 parts by weight of higher alkyldiethanolamine represented by the general formula (R2 is an alkyl group having 12 to 18 carbon atoms or an alkenyl group); 0.01 to 0.5 parts by weight of a higher fatty acid amide represented by a group or an alkenyl group) and a higher aliphatic metal salt represented by a general formula nyl group (M is a metal belonging to Group Ⅰ of the periodic table) .01~0.5
The present invention provides a method for producing a non-whitening transparent polypropylene film, characterized in that each part by weight is added.

The polypropylene used as a raw material in the method of the present invention is
Any material that is generally used for biaxial stretching may be used, and although there is no particular restriction, a material with a melt index of about 2 is usually used.

Further, examples of the higher fatty acid monoglyceride of general formula (1) used as a lubricant include glycerin monopalmitate, glycerin monostearate, and glycerin monooleate.

These lubricants contain 0 per 100 parts by weight of polypropylene.
．． 0.01 to 2 parts by weight, preferably 0.05 to 1 part by weight. Next, the general formula (
■) Examples of higher alkyl diethanolamines include:
Examples include myristyldiethanolamine, palmityldiethanolamine, stearyldiethanolamine, and oleyldiethanolamine.

These may be used alone or as a mixture of two or more. Examples of the higher fatty acid amide represented by the general formula (■), which is the second additive component, include myristylamide, palmitylamide, stialylamide, and oleylamide. These may be used alone or as a mixture of two or more. These compounds of general formula (■) and compounds of general formula (■) must have an alkyl group or alkenyl group in the molecule having 12 to 18 carbon atoms; The film may bleed and contaminate the contents, or the effect of preventing the whitening phenomenon may be insufficient. Further, examples of the higher fatty acid metal salt of general formula (■) which is the third additive component include zinc myristate, calcium myristate, zinc palmitate, calcium palmitate, zinc stearate, calcium stearate, and oleic acid. Examples include zinc and calcium oleate. These may be used alone or as a mixture of two or more, but in consideration of performance and food hygiene, zinc stearate alone is most preferred. The higher fatty acid metal salt of the general formula (■) must have an alkyl group or an alkenyl group in its molecule having 14 to 18 carbon atoms. Anything other than this has poor film processability and poor moldability. Adversely affect.

The blending ratio of these additives is 0.01 to 0.5 parts by weight, preferably 0.05 to 0.5 parts by weight of higher alkyl diethanolamine of general formula (■) per 10 parts by weight of polypropylene.
Weight part, higher fatty acid amide of general formula (■) is 0.01~
0.5 parts by weight, preferably 0.05 to 0.3 parts by weight, and 0.01 to 0.5 parts by weight, preferably 0.05 to 0.2 parts by weight of the higher fatty acid metal salt of general formula (■) used in amounts ranging from . If the amount is less than 0.01 part by weight, the anti-whitening effect will be insufficient, and if it exceeds 0.5 part by weight, the compatibility with propylene resin will be poor, resulting in poor moldability. At the same time, it adversely affects secondary processability (printing and adhesion) and is economically disadvantageous. There are no particular limitations on the means for blending additives or the means for forming a film in the method of the present invention, and any methods commonly used in the industrial production of polypropylene films can be used.

That is, each additive may be blended into polypropylene pellets using a mixer such as a Henschel mixer, or it may be prepared in advance as a master pellet and diluted with polypropylene as appropriate during film formation to obtain the desired ratio. It can also be done. In addition, as a biaxial stretching method,
A sequential stretching method using a tenter, a simultaneous stretching method such as a tube method, etc. can be used. According to the method of the present invention, by adding small amounts of highly food-safe additives, namely higher alkyl diethanolamines, higher fatty acid amides, and higher fatty acid metal salts to polypropylene containing higher fatty acid monoglyceride as a lubricant, the processability and mechanical properties of polypropylene are improved. It is possible to produce a transparent biaxially oriented polypropylene film that has an excellent anti-whitening effect without impairing the properties of the polypropylene.

Next, the present invention will be explained in more detail with reference to Examples.

Example polypropylene resin [MI (melt index 23 (
) = 2f/10 min, density = 0.905f/Cil]
Add a predetermined amount of each additive to 10 parts, mix for 2 minutes at 800C using a Henschel mixer, and mix at 230C using an extruder with a 4i diameter screw.
A strand was formed in the step and quenched to obtain a strand-cut pellet.

Next, this pellet was charged into an inflation molding machine having a 3i diameter screw and melted into a film at 25 crc to obtain an unoriented inflation film having a thickness of 120 μm. Next, this film was cut into squares of 10 CfR1 on each side, and simultaneously stretched 2.5 times in each of the vertical and horizontal directions at a temperature of 150 C using a biaxial stretching measuring device to obtain a biaxially stretched polypropylene film with an average thickness of 20 μm. Obtained.
The degree of whitening of the film thus obtained was measured,
The results are shown in the following table 1. The methods for measuring the physical properties shown in this table are as follows. Blooming index: Stretched film in 400C1 absolute dry atmosphere for 30 days and 65 days
ASTM D-1 before and after washing with ethanol after being left for a day
It is expressed as a difference of 2 in turbidity due to 003.

That is, first, the turbidity of the sample is measured, then the sample is sufficiently washed in an ethanol bath, left to dry, and the turbidity is measured again after the ethanol adhering to the surface is gone. If the turbidity of the sample before washing with ethanol is [A] and the turbidity of the sample after washing with ethanol is [B)', then the blooming index is expressed as [A] - [B]. Visual judgment: After leaving the film in an extremely dry atmosphere for 30 and 65 days, visually judge the degree of whitening at that time, and 5 indicates that there is no whitening at all. Those that appear are ranked as 1 and are divided into the following five stages...Those that do not cause any bleaching...
Very small amount of whitening (no particular problem in use)...Whitening occurs in a streaky cloud shape...Whitening occurs in a considerable state...Whitening clearly occurs over the entire surface of the film In the grass Compounds (4) to (8) in the additives have the following meanings.

As is clear from this table, when stearyl diethanolamine, oleylamide, and zinc stearate are used in combination with monoglycerol stearate as a lubricant, a significantly superior anti-whitening effect can be obtained.

Claims (1)

[Claims] 1 The lubricant is represented by the general formula ▲ Numerical formula, chemical formula, table, etc. ▼... (I) (R_1 in the formula is an alkyl group or alkenyl group having 14 to 18 carbon atoms) When producing a polypropylene film by biaxially stretching polypropylene containing higher fatty acid monoglycerides, there are general formulas ▲ mathematical formulas, chemical formulas, tables, etc. ▼ (II) (formula R_2 is an alkyl group or alkenyl group having 12 to 18 carbon atoms. III)
(R_3 in the formula is an alkyl group or alkenyl group having 12 to 18 carbon atoms) 0.
01 to 0.5 parts by weight and general formula (R_4COO)_2M
... (IV) (wherein R_4 is an alkyl group or alkenyl group having 14 to 18 carbon atoms, and M is a metal belonging to Group II of the periodic table) 0.01 to 0. A method for producing a non-whitening transparent polypropylene film, characterized in that 5 parts by weight of each are added. 2 The content of higher fatty acid monoglyceride of general formula (I) is 0.01 to 2 per 100 parts by weight of polypropylene.
The method according to claim 1, wherein the range is parts by weight. 3. The method according to claim 1, wherein the higher alkyldiethanolamine is myristyldiethanolamine, palmityldiethanolamine, stearyldiethanolamine or oleyldiethanolamine. 4. The method according to claim 1, wherein the higher fatty acid amide is myristylamide, palmitylamide, stearylamide, or oleylamide. 5. The method according to claim 1, wherein the higher fatty acid metal salt is zinc myristate, zinc palmitate, zinc stearate, zinc oleate, calcium myristate, calcium palmitate, calcium stearate, or calcium oleate.