JP2001026053A - Production of heat-shrinkable film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a heat-shrinkable film good in thickness accuracy and developing high heat shrinkability so as to make it possible not only to obtain a wide product but also to enable the enhancement of productivity due to an increase in molding speed or the like. SOLUTION: When an unstretched sheet obtained by the extrusion molding of a polyolefinic resin material is subjected to flat simultaneous biaxial stretch molding, the unstretched sheet is preheated at temp. satisfying T1<=Tp<=T2 [wherein Tp is preheating temp., T1 and T2 are each temps. wherein heat value of fusion measured from a low temp. side becomes 10% and 70% of ΔHma (the total heat value of fusion of the polyolefinic resin material)] and subsequently biaxially stretched at the same time at temp. becoming T1<=Tp+Te<=2×T2 (wherein Te is stretching temp.) to obtain a heat-shrinkable film wherein Le (film width at a time of the completion of a film forming process/Lm (film width at a time of the max. stretching) is 0.9-1, the stretching magnification of the film at a time of the max. stretching is 2-10 times in a flow direction and 2-10 times in a lateral direction and surface stretching magnification is 9-81 times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a heat-shrinkable film. More specifically, the present invention provides a film having good thickness and thinness precision, a wide product, improved productivity such as improved molding speed, and high heat shrinkability. The present invention relates to a method for producing a heat-shrinkable film.

[0002]

2. Description of the Related Art Heat shrinkable films are widely used in shrink wrapping applications such as individual wrapping, integrated wrapping, and shrink labels, utilizing the property of shrinking by heating. As such a heat-shrinkable film, many films using various thermoplastic resins such as a polyethylene resin, a polypropylene resin, a polyvinyl chloride resin, and a polyethylene terephthalate resin are commercially available.

As a method for producing a heat-shrinkable film, the film is generally produced by a biaxial stretching method of an inflation method for the purpose of adjusting the shrinkage ratio in the longitudinal direction and the lateral direction of the film. There was a problem in productivity, for example, it was difficult to improve the molding speed, and it was difficult to obtain a wide product.

On the other hand, in the production method by the flat biaxial stretching method, the sequential biaxial stretching method is generally used. However, the shrinkage rate tends to hardly increase, and the shrinkage rates in the longitudinal direction and the horizontal direction are adjusted. However, there are problems such as difficulty in performing

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has improved thickness, thinness and precision, and is capable of obtaining a wide product, and improving productivity by improving the molding speed. An object of the present invention is to provide a method for producing a heat-shrinkable film that can be made to exhibit high heat-shrinkability.

[0006]

Means for Solving the Problems As a result of diligent studies, the present inventors have found that the above-mentioned problems can be solved by performing flat biaxial stretching under specific molding conditions. Reached.

That is, the present invention provides a method for producing a film including a film-forming step of forming an unstretched sheet obtained by extruding a polyolefin resin material by a T-die method by a flat simultaneous biaxial stretching method. Wherein the film-forming step satisfies the following conditions (a) to (c): a method for producing a heat-shrinkable film.

(A) Pre-heating the unstretched sheet in a temperature range represented by the following equation (1), and then simultaneously biaxially stretching the sheet at a temperature satisfying the equation (2).

[0009]

Equation 1: T ₁ ≦ T _p ≦ T ₂

(In the formula 1, T _p represents the preheating temperature (° C.) of the unstretched sheet. T ₁ is calculated from the low temperature side when the total heat of fusion of the polyolefin resin material determined by DSC is ΔHma. Shows the temperature (° C.) when the calculated heat of fusion becomes 10% of the ΔHma. T ₂ shows the temperature (° C.) at which the heat of fusion calculated from the low temperature side becomes 70% of the ΔHma.)

[0011]

Formula 2: T ₁ ≦ T _p + T _e ≦ 2 × T ₂ (In Formula 2, _Te indicates a stretching temperature (° C.).)

(B) The film width at the end of the film forming process is L
e, when the film width at the time of the maximum stretching is Lm, Le and Lm satisfy the relationship of Expression 3.

[0013]

Formula 3: 0.90 ≦ Le / Lm ≦ 1.0

(C) The stretching ratio in the machine direction at the time of maximum stretching is 2 to 10 times, and the stretching ratio in the transverse direction is 2 to 1 times.
0 times, and the plane stretching ratio is 9 to 81 times.

The present invention also provides a method for producing the heat-shrinkable film, wherein the polyolefin resin material is a polypropylene resin material.

[0016]

Embodiments of the present invention will be described below. The method for producing a heat-shrinkable film of the present invention includes a film-forming step of forming an unstretched sheet obtained by extruding a polyolefin-based resin material by a T-die method by a flat simultaneous biaxial stretching method.

(1) Flat Simultaneous Biaxial Stretching Method The film forming step of the flat simultaneous biaxial stretching method in the present invention usually includes a preheating step of preheating an unstretched sheet,
And a stretching step of simultaneously biaxially stretching the preheated unstretched sheet, and preferably further includes a heat setting step of thermally setting the film obtained in the stretching step. Examples of the flat simultaneous biaxial stretching method include a batch simultaneous biaxial stretching method and a tenter simultaneous biaxial stretching method, and the tenter simultaneous biaxial stretching method is preferable from the viewpoint of productivity. In addition,
In the case of the tenter-type simultaneous biaxial stretching method, the method of preheating the unstretched sheet includes a method in which the sheet is heated only in a tenter furnace, and a method in which the sheet is heated in advance by a preheating roll and then further heated in a tenter furnace.

In the present invention, it is necessary that the film forming conditions in the film forming step by the flat simultaneous biaxial stretching method satisfy the following (a) to (c).

(A) Temperature conditions Preheating temperature In the method of the present invention, a polyolefin resin material is extruded by a T-die method, and the obtained unstretched sheet is preheated (preheating step). At this time, the preheating temperature is set to a temperature range satisfying the following equation 1. That is, the preheat temperature range of the undrawn sheet, and above T ₁ T ₂ less.

[0020]

Equation 1: T ₁ ≦ T _p ≦ T ₂

Here, in Equation 1, T _p indicates the preheating temperature (° C.) of the sheet. T ₁ is the temperature (° C.) at which the heat of fusion calculated from the low temperature side becomes 10% of the ΔHma, when the total heat of fusion of the polyolefin-based resin material determined by DSC is ΔHma, and preferably 15 ° C. %. T ₂ is a temperature (° C.) at which the heat of fusion calculated from the low temperature side becomes 70% of the ΔHma, preferably 60% or less, more preferably 50% or less, and particularly preferably 40% or less. Temperature.

If the preheating temperature of the unstretched sheet is lower than the above range, stretching becomes difficult. On the other hand, when the preheating temperature of the unstretched sheet is higher than the above range, the heat shrinkage property is deteriorated, and the accuracy of thickness and thickness is deteriorated.

[0023] In addition, the preheating temperature T _p is, does not necessarily mean the set temperature of the preheating zone. That is,
In the preheating step, the temperature of the substantially unstretched sheet is substantially equal to the above equation (1).
If the temperature of the unstretched sheet may not be able to be raised to the range represented by the above formula 1 because the preheating time cannot be sufficiently secured, the preheating may be performed. rolls and the set temperature of the preheating zone of the tenter oven may be set higher than T _2.

Stretching Temperature In the film-forming step of the present invention, the unstretched sheet is biaxially stretched simultaneously with the above-mentioned preheating step to form a film (stretching step). At this time, the stretching temperature is set to a temperature that satisfies Equation 2.

[0025]

Equation 2: T ₁ ≦ T _p + T _e ≦ 2 × T ₂

Here, in the expression 2, _Te indicates a stretching temperature (° C.). T ₁ , T _p , and T ₂ are the same as in Equation 1, respectively. If the stretching temperature is lower than the range satisfying the above formula 2,
It becomes difficult to stretch. On the other hand, when the stretching temperature
If it is higher than the range that satisfies the condition, the heat shrinkage property deteriorates.

(B) Film width In the method of the present invention, when the film width at the end of the above-mentioned film forming step is Le and the film width at the time of maximum stretching is Lm,
It is necessary that Le and Lm satisfy the relationship of Expression 3. That is, the ratio of Le and Lm (Le / Lm) is set to 0.90 or more.

[0028]

Equation 3: 0.90 ≦ Le / Lm ≦ 1.0

If the ratio Le / Lm is less than 0.90, the heat shrinkage characteristics will deteriorate. In addition, at the time of completion | finish of a film-forming process, in a batch type simultaneous biaxial stretching method, it means at the time of taking out a film from a stretching apparatus, and in a tenter type simultaneous biaxial stretching method, the film reached the exit of the tenter furnace. Means time.

(C) Stretching ratio In the method of the present invention, the stretching ratio at the time of the maximum stretching in the stretching step is 2 to 10 times, preferably 3 to 7 times in the direction of film flow (the direction of film take-up or the longitudinal direction).
2 to 10 times, preferably 3 to 7 times in the lateral direction (the direction perpendicular to or perpendicular to the flow direction). Further, the surface stretching ratio is 9 to 81 times, preferably 9 to 81 times.
It is 49 times, more preferably 16 times to 49 times. If the stretching ratio is lower than the above range, sufficient shrinkage cannot be obtained, and the film tends to be left behind and uneven in thickness.
On the other hand, if the stretching ratio is higher than the above range, it is difficult to form a film (formation of a film) under the above-mentioned temperature conditions, so that sufficient shrinkage cannot be obtained.

(D) Other film-forming conditions In the method of the present invention, the above-mentioned film-forming conditions (a) to (d)
Other conditions are not particularly limited as long as (c) is satisfied, but it is preferable to provide a heat setting step of heat setting the film obtained in the stretching step, following the stretching step.
The heat setting is performed immediately after the completion of the stretching step.
C., preferably 30 ° C. to 120 ° C., for about 1 second to 20 seconds.

The unstretched sheet may be a single layer or a multilayer sheet in which two or more layers are laminated. When the unstretched sheet is a multilayer, it may be a multilayer sheet composed of two or more layers of polyolefin-based resin materials, or may be a multilayer sheet in which layers other than the polyolefin-based resin material are laminated. It may be a combination.

In the case of a multilayer sheet in which layers other than the polyolefin resin material are laminated, the resin layer serving as a base material (specifically, a layer having a layer composition ratio of 50% or more) is a polyolefin resin material used in the present invention. Any layer may be used. Materials other than the polyolefin-based resin material constituting the layer having a layer composition ratio of less than 50% include, for example, polyamide, polyethylene terephthalate, polyvinyl alcohol and the like. A layer made of a material other than these polyolefin-based resin materials can be laminated on a base material layer made of the polyolefin-based resin material by coextrusion molding or the like.

When the unstretched sheet is a multilayer, the above T ₁ and T ₂ are determined from the total heat of fusion of the entire multilayer sheet (all layers). Whole multilayer sheet (all layers)
Can be determined, for example, by cutting out a multilayer sheet and measuring it by DSC.

(2) Polyolefin Resin Material The resin material used for film formation in the present invention is a polyolefin resin material mainly composed of a polyolefin resin. Examples of the polyolefin resin include a polyethylene resin, a polypropylene resin, and a polybutene-1 resin. Of these, preferred are polypropylene-based resins.

Examples of the polypropylene resin include a polypropylene homopolymer and a propylene / α-olefin random copolymer. Examples of the propylene / α-olefin random copolymer include a propylene / ethylene random copolymer and propylene / ethylene. -Butene-1 random copolymer etc. are mentioned. Preferably, the melting point is 145
℃ or lower, MFR (melt flow rate) 10 g / 10
Propylene / ethylene random copolymer or propylene / butene-1 random copolymer of less than or equal to 1 minute is used. These polyolefin resins may be used alone or as a mixture of two or more.

The polyolefin resin material used in the present invention includes, in addition to the polyolefin resin, other additional components such as additives used in ordinary polyolefin resin molding materials for films, etc. Can be arbitrarily blended within a range not to impair remarkably. Such optional components include antioxidants, crystal nucleating agents, clarifying agents, light stabilizers, ultraviolet absorbers, lubricants, anti-blocking agents,
Antistatic agent, antifogging agent, neutralizing agent, metal deactivator, coloring agent,
Dispersants, peroxides, fillers, and optical brighteners are included.
In addition to the polyolefin resin, a resin other than the polyolefin resin, for example, a petroleum resin, an acid-modified polyolefin resin, or the like can be optionally added.

(3) Heat Shrinkable Film The heat shrinkable film obtained by the method of the present invention is a layer formed of a film made of the polyolefin resin material of the present invention (hereinafter referred to as “polyolefin resin layer”). A) may be a single-layer film, but when a multi-layer sheet in which layers made of materials other than the polyolefin-based resin material are laminated as an unstretched sheet, layers other than the polyolefin-based resin layer are laminated. The heat-shrinkable film may be a multilayer film having two or more layers. When the heat-shrinkable film is a multilayer film, the polyolefin-based resin layer of the present invention has a layer composition ratio of 50% or more, preferably 60%.
What is necessary is just to comprise the above-mentioned base material layer. The thickness of the heat-shrinkable film (total thickness in the case of a multilayer film) is usually 5 to 100 μm, preferably 8 to 60 μm.

The heat-shrinkable film of the present invention utilizes the property of shrinking by heating, and can be used for individual packaging, integrated packaging,
It can be widely used for shrink packaging applications such as shrink labels. The heat-shrinkable film obtained by the method of the present invention has a preferable shrinkage ratio depending on its use. Generally, a film having a heat shrinkage ratio at 120 ° C. of 15% to 80% is suitably used.

[0040]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the invention. The methods for measuring and evaluating physical properties in the examples are as follows.

(1) Measurement of T ₁ and T ₂ by DSC (unit: ° C.) Using a DSC manufactured by Seiko, take 5.0 mg of a sample (polyolefin resin material) and hold it at 200 ° C. for 5 minutes. The mixture was cooled to 40 ° C. at a rate of temperature decrease of 10 ° C./min, and further melted at a rate of temperature rise of 10 ° C./min to obtain a heat of fusion curve. Based on the obtained heat of fusion curves, T ₁ and T ₂ were obtained.
I asked.

(2) Heat Shrinkage (Unit:%) The stretched film is cut into a square of 10 cm × 10 cm so that one side thereof is parallel to the flow direction of the film.
This was sandwiched between two metal meshes, and this was immersed in a silicon oil bath heated to 120 ° C. for 20 seconds. Immediately after the elapse of 20 seconds, the film was immersed in a separately prepared silicone oil bath at 23 ° C. for 20 seconds, and then the film was taken out from the wire mesh. The length of each film in the flow direction and the orthogonal direction was measured, and the heat shrinkage was determined.

[0043] (3) partiality Accuracy (%) Flow direction of the stretched film film and each cut out film full width into strips in the direction perpendicular average thickness d _a with a continuous thickness meter, the maximum thickness d _b, the minimum thickness measuring the d _c, the ratio of the average thickness as the thickness of the deflection width _{(d b -d c) / d} a ×
100 (%) was used as an index of the thickness accuracy. The smaller the value, the better.

[0044]

Example 1 (1) Polyolefin-based resin material Propylene / ethylene random copolymer powder 100 having an MFR of 2.5 g / 10 minutes and an ethylene content of 3.8% by weight
0.05 parts by weight of calcium stearate, 0.2 parts by weight of BHT (2,6-di-tert-butylhydroxytoluene), "Irganox1010" based on parts by weight
After mixing 0.05 parts by weight (manufactured by Ciba-Geigy) and 0.05 parts by weight of NA11 (manufactured by Asahi Denka Co., Ltd.) with a Henschel mixer, the mixture is granulated with a 30 mm single screw extruder and pelletized to obtain a polyolefin resin material. Was. This polyolefin resin material had T ₁ of 90 ° C. and T ₂ of 141 ° C.

(2) Formation of Unstretched Sheet The polyolefin resin material was melt-extruded at 230 ° C. by a T-die method to obtain a 430 μm thick unstretched sheet.

(3) Formation of Stretched Film The unstretched sheet is cut into a square of 9 cm × 9 cm so that one side thereof is parallel to the flow direction of the sheet. After preheating at 3 ° C. for 3 minutes, immediately at a stretching speed of 1 in an atmosphere of 90 ° C.
Simultaneous biaxial stretching is performed 5 times in the sheet flow direction at a speed of 0 m / min and 5 times in the orthogonal direction.
After heat setting in an atmosphere of 0 ° C. for 10 seconds, the stretched film was taken out. Table 1 shows the evaluation results.

[0047]

Example 2 A stretched film was formed in the same manner as in Example 1 except that the preheating temperature was changed to 100 ° C., the stretching temperature was changed to 120 ° C., and the heat setting temperature was changed to 120 ° C. Molded. Table 1 shows the evaluation results.

[0048]

Example 3 A stretched film was formed in the same manner as in Example 1 except that the preheating temperature was changed to 120 ° C., the stretching temperature was changed to 30 ° C., and the heat setting temperature was changed to 30 ° C. Molded. Table 1 shows the evaluation results.

[0049]

Example 4 In the forming of (3) stretched film in Example 1, simultaneous biaxial stretching was performed at a magnification of 5.25 times in the sheet flow (MD) direction and 5.25 times in the orthogonal (TD) direction. Immediately afterward, the chucks in both the MD and TD directions are simultaneously returned 5% from the maximum stretching width at a speed of 10 m / min, and the final stretching magnification is set to 5 times in the sheet flow direction and 5 times in the orthogonal direction. Then, the stretched film was taken out after heat setting for 10 seconds in the atmosphere described above. Table 1 shows the evaluation results.

[0050]

Example 5 In Example 1, (2) in forming an unstretched sheet, the thickness of the sheet was changed to 590 μm, and (3) in forming a stretched film, the preheating temperature was 110 ° C., the stretching temperature was 120 ° C. A stretched film was formed in the same manner as in Example 1 except that the heat setting temperature was changed to 120 ° C., and the stretching ratio was 6 times in the sheet flow direction and 6 times in the orthogonal direction.
Table 1 shows the evaluation results.

[0051]

Comparative Example 1 A stretched film was prepared in the same manner as in Example 1 except that the preheating temperature was changed to 145 ° C., the stretching temperature was changed to 145 ° C., and the heat setting temperature was changed to 145 ° C. Molded. Table 1 shows the evaluation results. Since the temperature range was out of the range of the present invention, the heat shrinkage ratio was small and the thickness accuracy was inferior to those of the examples.

[0052]

Comparative Example 2 In forming a (3) stretched film in Example 1, the preheating temperature was changed to 110 ° C., the stretching temperature was changed to 120 ° C., and the sheet flow was increased by 5.9 times in the machine direction and 5.9 times in the orthogonal direction. Immediately after the simultaneous biaxial stretching at the draw ratio, the chucks in the MD and TD directions are simultaneously returned by 15% from the maximum stretch width at a speed of 10 m / min, and the final stretch ratio is set to 5 in the sheet flow direction.
The film was heat-set in an atmosphere of 120 ° C. for 10 seconds, and then a stretched film was taken out. Table 1 shows the evaluation results. Since the ratio of the film width at the time of completion of the film-forming process to the film width at the time of the maximum stretching was out of the range of the present invention, the heat shrinkage was smaller than that of the examples.

[0053]

Comparative Example 3 In Example 1, (2) in forming an unstretched sheet, the thickness of the sheet was changed to 590 μm, and (3) in forming a stretched film, a preheating temperature was set to 110 ° C., a stretching temperature was set to 120 ° C. The heat setting temperature was changed to 120 ° C., and the stretching ratio was 10 times in the sheet flow direction and 10 times in the orthogonal direction.
A stretched film was formed in the same manner as in Example 1, except that the magnification was 100 times (plane stretching magnification: 100 times). The film was broken during the stretching process and could not be formed.

[0054]

[Table 1]

[0055]

According to the method of the present invention, it is possible to obtain a product with a good thickness and thinness, a wide width, an improvement in productivity such as an increase in molding speed, and a high heat shrinkability. Heat shrinkable film is obtained.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Tadashi Sezume 1 Toho-cho, Yokkaichi-shi, Mie Japan Polychem Corporation Material Development Center F-term (reference) 4F210 AA03 AA11 AE01 AG01 AR06 QC07 QD13 QD25 QG01 QG18 QW07

Claims (2)

[Claims] 1. A method for producing a film, comprising a film-forming step of forming an unstretched sheet obtained by extruding a polyolefin-based resin material by a T-die method by a flat simultaneous biaxial stretching method, A method for producing a heat-shrinkable film, wherein the film-forming step satisfies the following conditions (a) to (c). (A) Pre-heating the unstretched sheet in the temperature range shown in Formula 1 and then simultaneously biaxially stretching it at a temperature satisfying Formula 2. Formula 1: T ₁ ≦ T _p ≦ T ₂ (In the formula 1, T _p represents a preheating temperature (° C.) of an unstretched sheet. T ₁ is a total of the polyolefin resin material determined by DSC. When the heat of fusion is ΔHma, the temperature (° C.) at which the heat of fusion calculated from the low temperature side is 10% of the ΔHma is shown, and T ₂ is 70% of the ΔHma calculated from the low temperature side. (Equation 2 shows the temperature (° C.).) Equation 2: T ₁ ≦ T _p + T _e ≦ 2 × T ₂ (In Equation 2, _Te indicates the stretching temperature (° C.)) (b) Assuming that the film width at the end of the film forming step is Le and the film width at the time of the maximum stretching is Lm, Le and Lm satisfy the relationship of Expression 3. Equation 3: 0.90 ≦ Le / Lm ≦ 1.0 (c) The stretching ratio in the film flow direction at the time of maximum stretching is 2
Times to 10 times, the transverse stretching magnification is 2 to 10 times,
And the plane stretch ratio is 9 to 81 times. 2. The method for producing a heat-shrinkable film according to claim 1, wherein said polyolefin-based resin material is a polypropylene-based resin material.