JPH0617064B2 - Base film for opening tape - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a base film for an unsealing tape, which has excellent mechanical strength, and has improved heat shrinkage properties and fiber separation properties.

[Conventional technology]

A polypropylene (hereinafter abbreviated as PP) uniaxially stretched film has excellent optical properties, heat resistance, chemical resistance, and electrical properties, and also has excellent mechanical strength such as tensile strength and rigidity in the stretching direction. Widely used as various packaging films and tape-opening tape base films for cardboard boxes and the like.

However, a PP-axially stretched film containing a homopolymer as a main component, which has been stretched at a high ratio, has high rigidity but is easily cracked in the stretching direction. When a secondary process of applying an adhesive is performed and slitting into a tape shape having a width of 1 to 5 mm, fiber division occurs in the thickness direction of the film, and in severe cases, it may be cut.

Further, the uniaxially stretched film of the propylene / ethylene copolymer does not cause fiber separation and has good slits. However, the film is inferior in rigidity, has weak strength in the stretching direction, and has large heat shrinkage. Cause contraction.

[Problems to be Solved by the Invention]

An object of the present invention is to provide a base film for an opening tape, which does not cause fiber separation, has high mechanical strength in the stretching direction, has a low heat shrinkage rate, and is excellent in secondary processing suitability.

[Means for Solving the Problems]

As a result of intensive studies to solve the above problems, the present inventors have found that a specific propylene / ethylene copolymer and a small amount of atactic polypropylene (hereinafter referred to as AP) are added to a specific PP.
(Hereinafter, abbreviated as P) is formed into a film by a known method, and the film is flow direction (longitudinal direction).
It was found that a base film for an unsealing tape having improved heat shrinkability can be obtained by uniaxially stretching the film to prevent the fiber splitting during secondary processing while maintaining rigidity and strength, and completed the present invention.

That is, 80 to 20 parts by weight of polypropylene and 20 to 80 parts by weight of a propylene-ethylene copolymer having an ethylene content of 0.1 to 7.0% by weight are added to 0.
A film-like material is formed by using a mixture containing 1 to 3.0 parts by weight, and then the film-like material is stretched in the longitudinal direction at a draw ratio of 2 to 10 times at a temperature not higher than the melting point of the mixture. A base film for an opening tape, characterized in that

The PP used in the present invention is a homopolymer of propylene and has an isotactic index of 0.960 or more, preferably 0.970 or more, which is required in the boiling heptane-insoluble part. When the isotactic index is less than 0.960, the tensile strength of the film becomes weak, which is not preferable. In addition, the melt index (hereinafter M
Abbreviated as I) may be within the range generally used in the field of stretched films and stretched tapes, and the value measured by a method in accordance with JIS K-7210 at a temperature of 230 ° C. and a load of 2.16 kg is 0.2. To 10 g / 10 min, more preferably 0.5 to 8.0 g / 10 min. The compounding ratio of PP is 80 to 20 parts by weight, and when it exceeds 80 parts by weight, fiber splitting occurs, and when it is less than 20 parts by weight, the tensile strength is lowered and the heat shrinkage ratio is deteriorated.

The propylene / ethylene copolymer used in the present invention is a propylene / ethene copolymer obtained by copolymerizing a small amount of ethylene during propylene polymerization, and has an ethylene content of 0.1 to 7.0% by weight, preferably Is 0.5 to 5.
It is 0% by weight. MI is similar to PP, which is the main component
It is preferably 0.5 to 8.0 g / 10 minutes. The blending ratio of the propylene / ethylene copolymer is 20 to 80 parts by weight, and if it is less than 20 parts by weight, fiber splitting will occur, and if it exceeds 80 parts by weight, the tensile strength will be reduced and the heat shrinkage will be poor.

Atactic polypropylene used in the present invention (hereinafter referred to as A
(Abbreviated as PP) is a non-crystalline APP produced as a by-product in the polymerization process of PP, and has a molecular weight of 5,000 to 20,000. Further, it is preferable that this APP is steam stripped by a solvent recovery device and further dehydrated. The amount of APP added is 0.1 to 3.0 parts by weight, preferably 0.2 to 2.0.
Parts by weight. If the amount is less than 0.1 part by weight, the dispersibility of PP and the propylene / ethylene copolymer will be disturbed and the physical properties will be unbalanced. In particular, there is a variation in the effect of separation in the secondary processing. If it exceeds 3.0 parts by weight, the elongation becomes large and the tensile strength is lowered.

In addition, the PP resin mixture used in the present invention contains additives such as heat stabilizers, antioxidants, ultraviolet absorbers, antiblocking agents, lubricants, antistatic agents, pigments, dyes, and various other known additives. Agents may be added.

The base film for an opening tape of the present invention comprises 20 to 80 parts by weight of PP, 20 to 80 parts by weight of a propylene / ethylene copolymer, and AP.
After 0.1 to 3.0 parts by weight of P and various additives as required are blended and dry blended using a known blender or the like, an ordinary kneading machine such as a Banbury mixer,
Pelletize with a mixing roll, extruder, etc.

The pellets or the dry blended product before pelletization can be formed into a sheet or a film by an ordinary film or a sheet forming apparatus. For example, an unstretched film can be obtained by an inflation molding method using a circular die or a T die molding method using a T die.

The T-die molding method will be described in detail below.

The pellets or the dry blend described above are extruded at a resin temperature of 190 to 260 ° C. 6 with an extruder equipped with a T-die.
Cooling of the film-like material discharged from the T-die is preferably performed at a temperature of the cooling roll in the range of 30 to 90 ° C. The thus-obtained unstretched film is heated in a roll to have a stretching ratio of 2 to 10 times, preferably 4 to 7 times in a longitudinal direction between a pair of rolls having different surface speeds or in a multistage of two or more steps. Stretch. The stretching temperature at this time is 100 to 150 ° C, preferably 120 to 135 ° C, which is lower than the melting point of the mixture. If the stretching temperature is less than 100 ° C., stretch breakage is likely to occur, and if it exceeds 150 ° C., the film tends to wind around a sticky stretching roll, resulting in poor workability. If the stretching ratio is less than 2 times, the tensile strength cannot be exhibited, and if it exceeds 10 times, stretching breakage occurs frequently, which is not economical. Since the film obtained by stretching easily undergoes heat shrinkage, it is usually subjected to a treatment for 0.1 to 10 seconds at a temperature of not less than the stretching temperature, for example, a stretching temperature to 140 ° C., during which 10% or less, preferably 3 to 7%. It is preferable to keep it.

Although the thickness of the film varies depending on the object to be used for the tear tape, it is usually preferably 30 to 150 μm.

〔Example〕

 Hereinafter, the present invention will be described more specifically with reference to Examples.

Examples 1 to 6 and Comparative Examples 1 to 4 PP, propylene / ethylene copolymer and APP were mixed in a blending ratio shown in Table 1 with a blender, and then, with an extruder equipped with a T die, at a resin temperature of 230 ° C. It was discharged from the mold, cooled on a 90 ° C. cooling roll and solidified to obtain an unstretched film having a thickness of 0.39 mm. This unstretched film was heated on a roll heated to 120 ° C. and stretched 6.5 times between a pair of rolls having different surface speeds to obtain a 60 μm longitudinal uniaxially stretched film.

This longitudinally uniaxially stretched film was heat-treated at 130 ° C. for 5 seconds.

Corona discharge treatment is applied to both sides of this longitudinally uniaxially stretched film to impart secondary processing aptitude, one side is treated with silicon, dried in a dryer at a temperature of 120 ° C, and an adhesive is applied to the opposite side of the siliconized side. Then, it was dried again and wound into a roll.

Adhesive film wound into a roll was slit into a width of 5 mm to prepare 200 opening tapes. The slit was repeated 10 times to obtain an opening tape having a length of 10,000 m.

The unsealing tapes of Examples 1 to 6 had almost no splitting occurring in the tape thickness direction and cracks occurring in the tape width direction.

The opening tapes of Comparative Example 1 and Comparative Example 3 were sometimes separated, and the tape was cut, and the work was interrupted each time.

The unsealing tape of Comparative Example 2 caused heat shrinkage due to drying after application of the adhesive, and the adhesive film wound into a roll was hard, and the peeling at the time of slitting was heavy, and the working speed had to be slow. It was

The opening tape of Comparative Example 4 did not cause any trouble at the time of slitting, but when used as an opening tape, the elongation was large and it was unusable.

(Effects of the Invention) The longitudinally uniaxially stretched film obtained by the present invention has improved rigidity, high strength, small heat shrinkage, and separation at the time of slitting after secondary processing, and cracking are greatly improved, Almost no work troubles and it is a good base film for opening tape.

Claims (1)

[Claims] 1. Atactic polypropylene to 20 to 80 parts by weight of a propylene / ethylene copolymer having an ethylene content of 0.1 to 7.0% by weight with respect to 80 to 20 parts by weight of polypropylene.
A film-like material is formed by using a mixture containing 0.1 to 3.0 parts by weight, and the film-like material is stretched in the machine direction at a temperature not higher than the melting point of the mixture at a draw ratio of 2 to 10 times. A base film for an opening tape, which is characterized in that