JPS6136867B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to self-adhesive packaging films made from polypropylene resin compositions. More particularly, the present invention relates to a self-adhesive packaging film with improved cuttability.

This type of self-adhesive packaging film is widely used in households, restaurants, hotels, etc. for hermetically sealing food, preventing it from drying out when stored in a refrigerator, and when heating in a microwave oven. It exhibits effects such as preventing drying of food, preventing flavor or odor from dissipating or adsorbing odor during storage, and preventing dust from adhering when used for commercial purposes.

The cutting mechanism and usage method for this self-adhesive packaging film is such that a film with a width of 20 to 45 cm and a thickness of 10 to 20 microns is wrapped around a core material such as a paper tube, and is stored in a case such as a paper box. The film is picked up by a cutting blade called a ``saw blade'' attached to this case and cut to the appropriate length, and the adhesiveness of the film allows it to be used to clean the openings of food storage containers and the cuts of food. It is to be sealed.

The above-mentioned "saw blade" used for cutting film is generally a simple blade made by punching out a saw-shaped iron plate about 0.2 mm thick. The supporting case is also a coated cardboard box with a weight of about 350 to 700 g/ ^m2 , and has extremely low rigidity.

This type of film is required to be easily cut according to the user's will even with such a simple cutting mechanism, but in reality, the case and "saw blade" are deformed. In addition to this, the film may be deformed or cut at a position that is outside the ``saw blade''.

To be more specific, conventionally, films made of polyvinylidene chloride and polyethylene have been used as main raw materials, and when the former film is made of polyvinylidene chloride, if a tear is created in a part of the film when it is cut, the tear will break. It spreads out and cuts diagonally instead of cutting along the "saw blade".
Furthermore, the latter film made of polyethylene requires a considerable tensile force when cut, which not only causes the case to bend but also deforms the film.

Therefore, the object of the present invention is to be easy to cut, to avoid diagonal cuts, and to be able to easily cut according to the user's wishes using a simple cutting mechanism (referred to as cutability in this specification). The present invention provides a self-adhesive packaging film.

Other objects of the invention will become apparent from the following description of the specification.

The above object of the present invention is achieved by forming a film from a polypropylene resin composition whose crystallization temperature is increased by 2° C. or more by adding a nucleating agent or a crystallization promoter.

The present invention will be explained in detail below.

Generally, the crystallization temperature is determined by measurement using a differential thermal analysis device or a differential scanning calorimeter. It refers to the temperature measured using a device (manufactured by Rigaku Denki Kogyo) under the following measurement conditions.

〔Measurement condition〕

Sample pretreatment None Sample weight Approximately 10 mg Heating rate: 10°C/min Maximum temperature: 250°C Cooling rate: 10°C/min Atmosphere: In nitrogen gas flow When measuring the crystallization temperature of the sample using the above device and measurement conditions First, a melting peak is observed, and then, when the temperature is raised to 250°C, the temperature begins to decrease and a crystallization peak is observed. In the present invention, the temperature at the point where this crystallization curve is farthest from the baseline is defined as the crystallization temperature. The crystallization temperature measured in this way varies slightly depending on various additives.

Next, the polypropylene resin composition referred to in the present invention is primarily a propylene polymer. It also includes a copolymer with one or more other α-olefins (eg, ethylene, butene, hexene, etc.).

The means for increasing the crystallization temperature of the polypropylene resin composition of the present invention by 2°C or more is to increase the crystallization temperature by 2°C or more.
The polypropylene resin composition may contain a nucleating agent or a crystallization accelerator that can raise the temperature above .degree.

Such nucleating agents or crystallization promoters include aromatic and saturated aliphatic dicarboxylic acids, benzoic acid, nuclear-substituted benzoic acids, alicyclic carboxylic acids, and metal salts of these various acids, as well as silicic anhydride, thiol anhydride, etc. Glycolic acid, para-toluenesulfonic acid, talc, further bacic acid, aluminum hydroxide, thiodiglycolic anhydride, pt-butylbenzoic acid, pt-butylbenzoic acid aluminum salt, dibenzylidene sorbitol, etc. .

The crystallization temperature of such a nucleating agent or crystallization promoter increases as its content increases, and in the present invention, such a nucleating agent or crystallization promoter is It is sufficient to add only an amount that can raise the temperature of oxidation by 2°C or more. In the present invention, if the increase in crystallization temperature is less than 2°C, the above object of the present invention cannot be achieved.

The content of the nucleating agent or crystallization promoter of the present invention may be any amount that can raise the crystallization temperature by 2°C or more as described above, and generally depends on the type of the nucleating agent or crystallization promoter. It varies from 0.01 to 1.0
It may be about % by weight.

The nucleating agent or crystallization accelerator that can be used in the present invention is added to a resin composition to increase transparency and mechanical strength in a thick molded product manufactured by injection molding, for example. It is used for. However, it is currently considered worthless in the field of thin films. However, surprisingly, it was found that when a film was formed from a polypropylene resin composition in which the above-mentioned nucleating agent or crystallization promoter was added to raise the crystallization temperature by 2°C or more, the cutting properties were significantly improved. did.

In the present invention, general additives may be included in addition to the nucleating agent or crystallization promoter of the present invention described above. For example, it is optional to include antioxidants, stabilizers, antiblocking agents, antistatic agents, and the like. Note that the use of lubricants is not preferred since they impair self-adhesion.

The nucleating agent or crystallization accelerator of the present invention capable of raising the crystallization temperature by 2° C. or more can be incorporated into the polypropylene resin composition by any means, and may be kneaded using an extruder, for example.

That is, the nucleating agent or crystallization promoter of the present invention is kneaded into a polypropylene resin composition together with other additives such as antioxidants, stabilizers, and antistatic agents using an extruder or the like, and the mixture is made into pellets. , may be used as a raw material for film formation described below.

Next, we will discuss film formation.

For forming a film of the polypropylene resin composition whose crystallization temperature has been raised by 2°C or more according to the present invention, a conventional general film forming method for polypropylene can be employed. For example, the film may be made using an inflation method or a T-die method, and the extrusion temperature is about 200 to 280℃, extruded through an annular or flat slit, and cooled and solidified in water or on a cooling roll. do it. The thickness of the film according to the present invention may be similar to the thickness of conventional so-called laminate films, and is generally 10 to 20 μm.
It is said that

The present invention will be illustrated below with reference to Examples, but the embodiments of the present invention are not limited thereto.

[Example 1] Polypropylene resin composition (Mitsui Tosho Chemical Co., Ltd.,
Mitsui Noblen, JHH-G), sebacic acid 0.5
% by weight was added, and extruded pellets were obtained by a conventional method at 230°C. The crystallization temperature of this pellet was 120°C, compared to 115°C for the pellet without added sebacic acid.

The above pellets are processed using a T-die film forming machine with the following specifications.
It was made into a 12μ film.

Diameter 65mm Screw full flight type L/D 25 Die 600mm width Extrusion temperature 250°C Screw rotation speed 60rpm Cooling Water cooling This film had a haze of 1.5%, was completely transparent, and had sufficient self-adhesion. This is the case with the conventional general "saw blade" mentioned above (0.2 mm thick saw-shaped punched iron plate "saw blade"), 500 g / m ²
attached to a coated cardboard case. ) and attempted cutting with a "saw blade." As a result, it was possible to cut straightly by simply applying it to the saw blade and pulling it lightly, without any diagonal cuts.

[Example 2] Polypropylene resin composition (Mitsui Toatsu Chemical Co., Ltd.,
Mitsui Noblen, EFL-G) was added with 0.2% by weight of thiodiglycolic acid (anhydride), and Example-
Pellets were obtained by pressing in the same manner as in 1. The crystallization temperature of these pellets was 108°C, compared to 106°C for those without thioglycolic anhydride.
It was hot.

The above pellets were made into a 10 μm film using an inflation film forming machine with the following specifications.

Diameter 40mm Screw Full Light L/D 22 Die Diameter 20cm Folding Diameter 30cm Extrusion Temperature 210℃ Screw Rotation Speed 40rpm Cooling Water Cooling The haze of this film is 1.2%, making it completely transparent and self-adhesive. It was hot. When this film was cut in the same manner as in Example 1, it was found that although it was somewhat stronger than the film of Example 1, it was cut straight with just a slight pull compared to conventional products, and was not cut diagonally.

[Example 3] Pellets were obtained in the same manner as in Example-1 except that 0.1% by weight of dibenzylidene sorbitol was added in place of sebacic acid in Example-1. The crystallization temperature of this pellet was 118°C, an increase of about 3°C.

The obtained pellets were made into a 14μ film in the same manner as in Example-1.

This film had a haze of 1.1%, was completely transparent, and had sufficient self-adhesiveness. When this film was cut in the same manner as in Example 1, it cut easily and straight, and there were no diagonal cuts. Nakatsuta.

[Comparative Example 1] A film in which sebacic acid was not contained in Example 1 was obtained. When we examined the cutting properties of this film using the same method as in Example 1, we found that not only was the case with the saw blade deformed, but the film could not be cut along the saw blade. It was difficult.

[Comparative Example 2] Thiodiglycolic acid (anhydride) in Example 2
A film containing no was obtained. The cutting properties of this film were examined using the same method as in Example 1.
The film was deformed before being cut by the "saw blade".

[Comparative Example 3] Thiodiglycolic acid (anhydride) in Example 2
Pellets were obtained in the same manner except that the amount added was 0.05% by weight. The crystallization temperature of this pellet is 107
It was warm at ℃. This pellet was formed into a film in the same manner as in Example 2. When the cuttability of this film was examined using the same method as in Example 1, the film was deformed before being cut by the "saw blade", as in Comparative Example 2.

Claims (1)

[Claims] 1. A self-adhesive packaging film with excellent cuttability, characterized in that it is formed from a polypropylene resin composition whose crystallization temperature has been raised by 2°C or more by adding a nucleating agent or a crystallization promoter.