JPH0493225A - Sealant film - Google Patents

Abstract

PURPOSE:To enable the title sealant film to have favorable sealing properties, high sealing strength, excellent film strength, low thermal shrink properties, excellent dimensional stability, generate no creases at the time of heat sealing and make a mult-layer film into a thin film, by a method wherein since the title film is comprised of resin consisting mainly of linear low density polyethylene, stretched at least three times in a lateral direction and an area shrinkage factor and a shrinkage ratio between a longitudinal and lateral directions are within a specific range. CONSTITUTION:Raw sealant film is obtained by a method wherein raw fabric which is substantially unstretched is molded of resin consisting mainly of linear low density polyethylene, the raw fabric is stretched biaxially and then heat-treated the same. It is good to make that draw ratio is at least three times and less than 8 times and the product of draw ratios of biaxial directions is at least 9 times and less than 50 times from view points of biaxial stretchability and physical properties of a film to be obtained. An area shrinkage factor is not exceeding 30% at 100 deg.C and a stretching temperature, the draw ratio and a heat treatment condition are combined by selecting them appropriately. With this construction, it is prepared that a shrinkage ratio of a longitudinal direction : lateral direction or the lateral direction : longitudinal direction of a biaxially stretched film becomes within a range of 0.5-2.0.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a sealant film, and more particularly, to a biaxially stretched sealant film made of a resin mainly composed of linear low-density polyethylene. be.

[Conventional technology]

Traditionally, sealant films include low density polyethylene (LDPE) and high density polyethylene (HDPE).
), linear low density polyethylene (LLDPE), polypropylene (PP), ethylene-vinyl acetate copolymer (E
Films made of VA) and the like are known. These films are unstretched or uniaxially stretched films manufactured by the T-die casting method or the inflation method.

Each of the above-mentioned sealant films is widely used because of its characteristics such as low cost and high strength of the heat-sealed portion.

However, because blind molecular orientation is not imparted, the film strength is low, and in order to increase the strength, the film must be made thicker.For this reason, the laminated base material is a film with excellent transparency. However, because of the sealant film, its excellent transparency cannot be fully utilized.

In particular, the transparency of low density polyethylene blown film is very poor.

Although the uniaxial stretching method imparts molecular orientation and increases strength, due to the anisotropy of molecular orientation, there are problems such as wrinkles occurring on the sealing surface during heat sealing, reducing the value of the part.

Recently, a sealant film made of biaxially stretched LDPE has been proposed.

For example, Japanese Patent Application Laid-open No. 60-187544 discloses that the thermal shrinkage rate at boiling water temperature is 3 in the vertical and horizontal directions.
0% or more in JP-A No. 62-59037, and JP-A No. 62-201229 has a heat shrinkage rate of 10 to 50% in the vertical and horizontal directions at 95°C. A material with an area shrinkage rate of 20% or more at 90°C is proposed in JP-A-63-214445, and a heat shrinkage rate of 6% or more in each of the vertical and horizontal directions at 75°C is proposed. .

In addition, each of the above-mentioned sealant films was biaxially stretched by the tubular method.

[Problem to be solved by the invention]

However, although the above-mentioned sealant film made of biaxially stretched LDPE has satisfactory strength due to the stretching orientation, it has large heat shrinkability, which causes wrinkles in the heat-sealed portion and limits the heat-sealing temperature conditions. However, there are disadvantages in terms of workability and economy.

In addition, in biaxially stretched films, the longitudinal (MD)
Direction: Horizontal (TD) direction or Horizontal (TD) direction: Vertical (
If the shrinkage ratio in the MD) direction is unbalanced, it will be affected by the anisotropy of molecular orientation, and as a result, due to the anisotropy of molecular orientation similar to that of the film obtained by -axial stretching, A similar problem arises.

The purpose of the present invention is to take advantage of the characteristics of biaxially stretched films, and also eliminate the drawbacks of the above-mentioned biaxially stretched films,
For example, polyethylene terephthalate (PET),
The object of the present invention is to provide a sealant film that is laminated onto a base film such as cellophane, oriented polypropylene (OPP), oriented nylon (ONY), etc., and is suitable as a multilayer film for food packaging or a multilayer film for general packaging.

[Means to solve the problem]

That is, the gist of the present invention is made of a linear low-density polyethylene resin, stretched 3 times or more in each of the longitudinal and transverse directions,
The present invention relates to a sealant film having an area shrinkage rate of 30% or less at 100°C and a shrinkage ratio in each of the longitudinal and transverse directions ranging from 0.5 to 2.0.

The present invention will be explained in detail below.

The sealant film of the present invention is made of a resin mainly composed of linear low-density polyethylene.

Linear low-density polyethylene is a copolymer of ethylene and α-olefin, and unlike low-density polyethylene, which is produced by the conventional high-pressure method, it is produced by a low-pressure method.
It can be produced at low cost due to low equipment costs and energy consumption.Alpha-olefins copolymerized with ethylene include butene-1, pentene-1, hexene-1, octene-1,4-methylpentene-1. etc.

The structural difference between high-pressure low density polyethylene and linear low density polyethylene is that the former has a multi-branched molecular structure, and the latter has a linear molecular structure.

There are various methods of manufacturing linear low-density polyethylene, and the physical properties vary depending on the manufacturing method.
10m1n) is preferably 0.5 to 3.0.

If the MI is less than 0.5, the extrudability is insufficient, and when forming the original fabric as described below, for example, instability in sheet forming due to surging causes thickness fluctuations.
Furthermore, cooling spots caused by this often cause variations in transparency or crystallinity, making it difficult to obtain a raw fabric with excellent physical properties and stretchability.

If the MI is greater than 3.0, the melt tension is low, and the raw material may be affected by, for example, the drooping of bubbles during inflation molding or the occurrence of ripples due to unstable contact with the cooling drum during T-die molding. There are disadvantages in molding. Furthermore, due to the low molecular weight, the stretchability and degree of stretch orientation are lowered, which is thought to be due to the shorter molecular chains and less entanglement between the molecular chains. As a result, the physical properties of the film deteriorate, making it difficult to obtain a desired stretched film.

Moreover, the linear low density polyethylene used in the present invention preferably has a density (g/cc) in the range of 0.910 to 0.940.

If the density is less than 0.910, the flexibility of the film will be excellent, but problems will arise in processability;
If it is larger than 940, the flexibility of the film will be impaired.

Note that high-pressure polyethylene, ethylene-vinyl acetate copolymer ionomer, ethylene-propylene copolymer, etc. may be mixed with the linear low-density polyethylene as long as it does not interfere with the purpose of the present invention. I can do it. Furthermore, heat and ultraviolet stabilizers, pigments, antistatic agents,
There is no problem in adding fluorescent agents, lubricants, etc.

The sealant film of the present invention is produced by molding a substantially unoriented raw film from a resin mainly composed of linear low-density polyethylene as described above, biaxially stretching the raw film, and then heat-treating the film. can get.

The raw fabric may be formed according to a conventional sheet forming apparatus and forming method, and for example, a T-die forming method using a T-die may be used.

Biaxial stretching may be any of the simultaneous biaxial stretching method, tubular simultaneous biaxial stretching method, and sequential biaxial stretching method,
A biaxial stretching method is preferably used.

The stretching temperature is in the range of -50°C to -10°C, the melting point of the raw material resin, preferably in the range of -30°C to melting point = 13°C.

If the stretching temperature is below the melting point -50°C, the molecular chains have poor mobility and are likely to break during stretching, and even if stretching is possible, the stretching ratio will not increase, making it difficult to obtain a stretched film with excellent physical properties. It is.

On the other hand, when the melting point is higher than -10°C, as can be inferred from the multiple peaks in the DSC curve peculiar to linear low-density polyethylene, the linear low-density polyethylene is partially melted and the orientation effect by stretching cannot be sufficiently obtained. Furthermore, even if the film is apparently stretched, stretching irregularities may occur in the film, and the transparency is not sufficient.

The stretching ratio is 3 times or more in the longitudinal and transverse directions from the viewpoint of biaxial stretchability (easiness of stretching) and physical properties of the obtained film.
The product of the stretching ratios in two directions is preferably 9 times or more and less than 50 times. The thickness of the film is usually in the range of 5 to 50 microns, preferably 10 to 35 microns.

Note that the stretching speed is not particularly limited, and an appropriate stretching speed can be selected.

On the other hand, the heat treatment temperature ranges from -40°C to the melting point of the raw resin.
A temperature of 3°C is preferred. If the heat treatment temperature is lower than the melting point -40°C, the resulting film lacks dimensional stability, and when used as a sealant film, the film tends to shrink during heat sealing and cause wrinkles on the sealing surface. On the other hand, if the melting point is higher than -3°C, the molecular orientation inside the film caused by stretching will flow and collapse, resulting in a marked decline in film properties. The heat treatment time is preferably 5 seconds or more. Even if the heat treatment temperature is within the above temperature range,
When the heat treatment time is less than 5 seconds, the obtained film lacks dimensional stability, and when used as a sealant film, the film tends to shrink during heat sealing and wrinkles are likely to occur on the sealing surface.

The sealant film of the present invention can be produced by appropriately selecting and combining the above-mentioned stretching temperature, stretching ratio, and heat treatment conditions to produce a biaxially stretched film in the longitudinal (MD) direction: transverse (TD) direction or in the transverse (TD) direction; The shrinkage ratio in the (MD) direction is set to be in the range of 0.5 to 2.0.

Further, the sealant film of the present invention can be subjected to known surface treatments such as corona treatment and flame treatment.

The sealant film of the present invention is used as a desired multilayer film by laminating it on a base film by a known method.

Lamination can be easily performed by, for example, extrusion lamination, dry lamination, or the like. Extrusion lamination is a method in which a thermoplastic resin that can be formed into a film, which will become the adhesive layer, is extruded onto a base film through a thin slit in the T-die of an extruder using the melt extrusion method, and a sealant film is laminated, and the film is cooled and solidified. This is the way to do it. Dry lamination is a method in which an organic solvent-based adhesive such as urethane adhesive is applied to a base film, the solvent is evaporated off by drying, and then a sealant film is laminated by heat and pressure bonding.

The processing conditions during the above lamination are appropriately selected depending on the type of base film.

〔Example〕

Hereinafter, the present invention will be specifically explained based on Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

In the following examples, a sequential biaxial stretching method using a longitudinal stretching device using rolls and a horizontal stretching device using a hot air oven type tenter was adopted.

In addition, the measurement items shown in the main text and the following examples were carried out by the following method.

1. Shrinkage rate A film cut into a square of 10 cm in length and width is immersed in a silicone oil bath at a specified temperature for 10 minutes and taken out.
The vertical and horizontal lengths were measured and calculated using the following formula.

Shrinkage rate (%) = (10-A or B) X10 area shrinkage rate (%) = 100-AXB However, A and B indicate length and width after immersion (in am).

2. Shrinkage ratio Calculated using the following formula.

3. Density (ρ) Measured at 23°C using a density gradient tube in accordance with JIS K 6760 (unit: g/cc).

4. Melting point differential scanning calorimeter (DSC-II manufactured by PerkinElmer)
The endothermic main peak temperature on the melting curve determined by the measurement was taken as the melting point.

Measurement conditions: Measurement sample IO~30■ Temperature increase rate 10°C/mi 5, MI (melt index) Measured at 190°C in accordance with JIS K 6760 (unit: g/10 minutes).

6. Lamination method A: Nidry laminate Use the adhesive Takelac A615/A65/ethyl acetate manufactured by Nitomoe Pharmaceuticals. Dry laminated at about 80℃, 40℃
It was aged for 4 days at ℃.

B: Extrusion laminate Extrusion laminated using low density polyethylene.

Example 1 Density at 23°C 0.920 g/cc, melt index 0.9 g/10 m1n, flow ratio 2
1. Copolymerization component 4-methylpentene-1, copolymerization amount 10
% by weight of ethylene-α-olefin copolymer, D
The main peak temperature for the melting curve by SC is 125°C
Linear low-density polyethylene was melt-kneaded at 200 to 250°C, extruded through a T-die maintained at 250°C, and brought into close contact with a cooling roll by the known air knife method to obtain an unstretched sheet (this unstretched The sheet was used as the original fabric and was also used in the following examples).

The above raw sheet is sequentially introduced into a biaxial stretching device, and stretched 5 times in both the length and width at a longitudinal stretching temperature of 112°C and a transverse stretching temperature of 100°C, and the stretched film is immediately heat treated for 5 seconds at a heat treatment temperature of 120°C. Thereafter, it was cooled to room temperature and rolled up.

The obtained stretched film had a thickness of 20 μm and an area shrinkage rate of 16% at 100° C.

The above film was laminated on a 15 μm thick nylon biaxially stretched film (general product grade/Santonil SN manufactured by Mitsubishi Kasei Polytechnics) by dry lamination method (A) or extrusion lamination method (B), and heat-sealed at a temperature of 140°C and 1150°C. 1160℃, sealing pressure 2kg/
cm2 and sealing time of 1 sec, no wrinkles were observed on the sealing surface under any conditions, and a good sealing strength of 4 to 5 kg/15 mm was obtained.

Example 2 A film stretched under the same conditions as Example 1 was immediately heat treated at a heat treatment temperature of 100° C. for 5 seconds, cooled to room temperature, and wound up.

The obtained stretched film had a thickness of 20 μm and an area shrinkage rate of 30% at 100° C.

When the above film was laminated to a nylon biaxially stretched film in the same manner as in Example 1 and heat-sealed, no wrinkles due to shrinkage of the sealing surface were observed, and the sealing strength was 4.
A good sealing area of ~5 kg/15 mm was obtained.

Comparative Example 1 A film stretched under the same conditions as Example 1 was immediately heat treated at a heat treatment temperature of 120° C. for 3 seconds, cooled to room temperature, and wound up.

The obtained stretched film had a thickness of 20 μm and an area shrinkage rate of 33% at 100° C.

When the above film was laminated to a nylon biaxially stretched film in the same manner as in Example 1 and heat-sealed, the sealed surface shrank and wrinkles were observed on the sealed surface, so it had no value as a product. Met.

Comparative Example 2 A film stretched under the same conditions as Example 1 was immediately heat treated at a heat treatment temperature of 75° C. for 5 seconds, cooled to room temperature and wound up.

The obtained stretched film had a thickness of 20 μm and an area shrinkage rate of 50% at 100° C.

When the above film was laminated onto a biaxially stretched nylon film and heat sealed in the same manner as in Example 1, the sealed surface shrank and wrinkles were observed on the sealed surface.

The results of the above Examples and Comparative Examples are summarized in Table 1.

The meaning of each symbol in the table is as follows.

○: Good with no wrinkles △: Slight wrinkles occur ×: Wrinkles appear Moreover, the shrinkage ratio is a value calculated using the following formula.

Table [Effects] According to the present invention described above, a sealant film having the following excellent properties is provided.

(1) The advantages of using linear low-density polyethylene resin as a raw material can be enjoyed as is, with good sealing properties and high sealing strength.

(2) Excellent film strength, low heat shrinkage and excellent dimensional stability.

(3) No wrinkles occur during heat sealing.

(4) By using it as a sealant film for a multilayer film, it is possible to make the multilayer film thinner.

Therefore, the industrial value of the present invention is great.

Applicant: Mitsubishi Kasei Polytech Co., Ltd. Agent: Patent Attorney Oka 1) Kazuhiko

Claims (1)

[Claims] (1) Made of resin mainly composed of linear low-density polyethylene, stretched at least 3 times in the vertical and horizontal directions at 100°C.
A sealant film having an area shrinkage rate of 30% or less and a shrinkage ratio in each of the vertical and horizontal directions ranging from 0.5 to 2.0.