JP2611392B2 - White polyolefin film and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is a polyolefin film having white opacity, pseudo paper-like gloss, and pearly gloss, and has various printability, dimensional stability, water resistance (moisture), The present invention relates to a white polyolefin film suitable for packaging and decoration of printing paper, various labels, confectionery, snacks and the like which require chemical resistance, and a method for producing the same.

[Prior Art] Conventionally, it is well known that a large amount of white inorganic particles are added to a thermoplastic resin to obtain a white film, and the film is monoaxially or biaxially stretched (Japanese Patent Publication No. 46-40794, JP-A-50-90644). This film becomes white and opaque because peeling occurs at the interface between the resin and the inorganic particles when the film is stretched, and fine voids are generated inside the film and fine cracks are generated on the surface. This is because the light is scattered on the film surface and inside.

Also, a technique of blending a methylpentene polymer with polypropylene or a propylene copolymer and biaxially stretching is known (JP-A-52-58773, 52-58774).
etc).

[Problems to be Solved by the Invention] In order to obtain a white film, a film to which a large amount of inorganic particles are added is subjected to secondary processing such as printing, punching, automatic packaging, etc., when surface free particles generated by surface cracks are generated. There are drawbacks in that the finish of printing is remarkably reduced, and that many internal voids are generated, resulting in poor mechanical strength and remarkably lowering the efficiency of secondary processing.

In addition, a film obtained by blending a methylpentene polymer with polypropylene and stretching by a conventional uniaxial and biaxial stretching method can obtain a roughened surface and a tearing property, but is a pseudo-paper-like, white, highly concealable, A film with high mechanical strength cannot be obtained.

The present invention, as a result of intensive studies on white polyolefin films, is white and excellent in concealing properties, has a pearly luster, has high mechanical strength, is suitable for various printing papers, various labels, packaging and decoration of confectionery and snacks and the like. And a method for producing the same.

[Means for Solving the Problems] The present invention has an optical density (OD) of 0.1 or more and a glossiness of 40%.
A polyolefin film as described above, wherein the strength in the longitudinal direction of the film is 8 kg / mm ² or more, and the sum of the Young's modulus in the longitudinal direction and the width direction is 250 kg / mm ² or more. In order to further obtain the white polyolefin film, the isotactic index (II) is 80% or more and the intrinsic viscosity is 1.2
A methylpentene polymer having an n-heptane extraction residue of at least 40% was added to 100 parts by weight of polypropylene of 3.5 dl / g to 5 dl / g.
~ 50 parts by weight of the resin added is melt-molded into a sheet or tube, then finely stretched within the elastic limit at a temperature of 120 ° C or less, and then at a temperature of 120 ° C to 170 ° C, at least uniaxially. The present invention relates to a method for producing a white polyolefin film, which is characterized by stretching.

In the present invention, the optical density (OD) of the film is 0.1 or more, preferably 0.2 or more. When the optical density (OD) is less than 0.1, the whiteness and the concealing property are inferior, and the printed characters and pictures are seen from the back side, and the practicability is inferior.

The glossiness is 40% or more, preferably 50% or more.
When the glossiness is less than 40%, the roughness of the film surface is large,
When printed, bleeding of the ink occurs and clear characters and pictures cannot be obtained, and the pearl-like elegant and noble gloss, which is one of the features of the film, is impaired.

Further, the strength of the film of the present invention in the longitudinal direction is 8 kg / mm ² or more, preferably 10 kg / mm ² or more. Longitudinal strength
If it is less than 8 kg / mm ² , the film is dimensionally deformed or torn during printing, and the efficiency of the secondary processing is significantly reduced.

The sum of the Young's modulus in the longitudinal and width directions of the film is
It is at least 250 kg / mm ² , preferably at least 300 kg / mm ² . The sum of the Young's modulus of the film end sag during printing processing is less than 250 kg / mm ^2, or occurred misalignment of printing in the central portion and the end portion,
It is inferior in stamping workability and handling property for label use, and has poor form retention and poor content protection when used for packaging.

The film of the present invention has a density of 0.7 g / cm ³ or more, preferably 0.8 g / cm ³ or more. If the density is smaller than 0.7 g / cm ³ , the void volume in the film is large, and productivity and mechanical strength are often poor.

The thickness of the film of the present invention in the printing enemy, punching processing of labels and the like, and secondary processing properties such as automatic packaging,
It is 5 to 100 μm, preferably 10 to 60 μm. When the thickness is smaller than the above range, the concealing property, strength and shape retention are insufficient, and when the thickness is larger, the workability and the handling property are not preferable.

The polyolefin referred to in the present invention is a mixture of a polypropylene homopolymer or copolymer and a methylpentene polymer or copolymer. Polypropylene and methylpentene can be used properly depending on the application. When heat resistance and mechanical properties are important, a homopolymer is used, and when softness and flexibility are important, a copolymer is preferable. When it is a copolymer, it is a random or block copolymer with another α-olefin,
The copolymerization amount is preferably set to 10 mol% or less. When another resin is blended, the blending ratio is preferably 10% by weight or less.

 Next, a method for producing the film of the present invention will be described.

The isotactic index (hereinafter abbreviated as II) of the polypropylene or copolymer needs to be 80% or more, and when heat resistance and solvent resistance are required, II is preferably 90% or more. .

The intrinsic viscosity [η] of the polypropylene is 1.2 dl / g or more.
It is necessary to be 3.5 dl / g, preferably 1.5 dl / g
2.2 dl / g. When [η] is smaller than the above range, castability and stretchability are particularly deteriorated. When it is larger, not only melt extrudability is deteriorated, but also film formation becomes difficult.

Next, the methylpentene polymer blended with the polypropylene or copolymer is a methylpentene homopolymer or copolymer, which is a polymer of 4-methyl-1-pentene alone or a random copolymer with another α-olefin. 4,4-methyl-1-pentene monomer unit is 80 mol% or more. The extraction residue of n-heptane of the polymer must be at least 40%, preferably at least 50%. 40% n-heptane extraction residue
If the optical density (OD) is less than 0.1,
No whiteness or opacity is exhibited. The melting point (Tm) of the polymer is 200 to 240 ° C., and the crystallization temperature (Tmc) is 180 to 220.
When the temperature is ° C, the optical density (OD) becomes 0.1 or more, and the whiteness and the concealing property are improved. In terms of dispersibility, the MI of the polymer is preferably from 2 to 200 g / 10 min, and more preferably from 10 to 100 g / 10 min, because the glossiness is high. The addition amount of the methylpentene polymer is in the range of 5 to 50 parts by weight, preferably 10 to 40 parts by weight based on 100 parts by weight of the polypropylene. If the amount is less than 5 parts by weight, the optical density (OD) becomes small and the whiteness and the concealing property are inferior. If the amount exceeds 50 parts by weight, the dispersibility deteriorates and the stretching becomes unstable, resulting in over-voiding inside the film and mechanical It becomes inferior to the characteristic.

In addition, the film of the present invention does not impair the purpose,
A nucleating agent, an antioxidant, a heat stabilizer, a lubricant, an antistatic agent and the like may be added.

Next, the mixed resin is supplied to an extruder heated to 260 ° C. to 310 ° C., melt-molded into a sheet or a tube, and then the sheet or tube is subjected to fine stretching within an elastic limit at a temperature of 120 ° C. or less. After that, it is necessary to stretch the film at a temperature of at least 120 ° C. to 170 ° C. at least uniaxially. Stretching by a known stenter-type sequential or simultaneous biaxial stretching method or a tube-type simultaneous biaxial stretching method alone gives a white and highly concealable film having an optical density (OD) of 0.1 or more, which is the object of the present invention. Because there is no.

Fine stretching within the elastic limit is defined as stress at the stretching temperature.
-Stretching up to the yield point stress of the strain curve.

The reason why the fine stretching within the elastic limit is effective is to increase the sea-island structure in the mixed sheet of polypropylene and methylpentene polymer, which are basically incompatible resins, to generate microvoids at the interface between them, In this case, diffuse reflection at the interface due to the difference in refractive index is increased, and whiteness and concealment are developed.

In the stretching after the fine stretching within the elastic limit, in the case of uniaxial stretching, the stretching temperature is 120 ° C. to 170 ° C. and the stretching ratio is 3 in area ratio by a stretching method based on a difference in peripheral speed between rolls or a stenter stretching method. When the ratio is 10 to 10 times, preferably 4 to 8 times, the film forming property becomes good.

In the case of biaxial stretching, the film is biaxially stretched by a stenter sequential or simultaneous biaxial stretching method or a tube simultaneous biaxial stretching method. In the case of simultaneous biaxial stretching, the stretching temperature is 145
The range of -165 ° C is preferable because the film-forming property is good, and when the stretching ratio is 10 to 50 times, preferably 20 to 40 times, the film-forming stability becomes good and the gloss becomes high.

In the case of sequential biaxial stretching, the film is stretched 3 to 7 times in the longitudinal direction at a stretching temperature of 120 to 150 ° C.
The film is stretched 5 to 15 times in the width direction at a stretching temperature of 70 ° C.

The film stretched as described above is 160-175 ° C.
For several seconds. At this time, when the heat treatment is performed while allowing a few percent relaxation, the dimensional stability is improved. Further, if necessary, surface activation treatment, for example, corona discharge treatment or plasma treatment under various gases such as N ₂ , CO _2, etc., to increase the surface tension, so that the adhesion or deposition of the printing ink can be improved. Good adhesion to metal.

In addition, a resin such as an ethylene-propylene random copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-vinyl acetate copolymer, an ionomer, or the like, may be used for in-line or off-line resin. May be laminated on both or one side.

The white polyolefin film obtained by the above method is suitable not only for packaging and decoration of various printing papers, various labels, confectionery, snacks and the like, but also has good properties as a base film for an adhesive tape.

[Effect of the Invention] The white polyolefin film of the present invention has the following excellent points.

(1) It is white, has excellent concealing properties, has high gloss on the film surface, has excellent printability, and has mechanical strength, dimensional stability and solvent resistance required in the secondary processing step.

(2) Since it does not substantially contain an inorganic filler, the internal voids are minute, and are excellent in moisture resistance required for packaging confectionery and the like.

(3) It is excellent in film forming property and cost.

[Measurement Method] Next, measurement methods and terms of each characteristic value in the present invention will be summarized below.

(1) Intrinsic viscosity ([η]) 0.1 g of sample was completely dissolved in 100 ml of tetralin at 135 ° C.
This solution is measured with a viscometer in a thermostat at 135 ° C., and the intrinsic viscosity is determined from the specific viscosity S according to the following equation.

 The unit is dl / g.

[Η] = S / 0.1 × (1 + 0.22 × S) (2) Isotactic index (II) or n-heptane extraction residue The sample is vacuum dried at 130 ° C. for 2 hours. From now on weight W
(Mg) of the sample, put it in a Soxhlet extractor and boil
-Extract with heptane for 12 hours. Next, the sample is taken out, sufficiently washed with acetone, vacuum-dried at 130 ° C. for 6 hours, and the weight W ′ (mg) is measured.

II (%) = W '/ W x 100 (3) Breaking strength According to JIS K-6782.

(4) Young's modulus According to ASTM D-882-75b.

(5) Melting temperature (Tm) / Melting crystallization temperature (Tmc) 5 mg of a sample is set on a scanning calorimeter DSC-II type (manufactured by Perkin Elmer), and the temperature is raised at a rate of 20 ° C./min under a nitrogen stream. It is measured from room temperature, and the endothermic peak temperature accompanying melting is defined as the melting temperature (Tm).

Similarly, after keeping the sample at 280 ° C. for 5 minutes and then lowering the temperature to room temperature at a temperature lowering rate of 20 ° C./min, the heat release peak temperature accompanying crystallization is changed to the melting crystallization temperature Tm.
c.

(6) Melt flow index (MI) Measured under ASTM-D-1238 at 260 ° C and 5 kg.

 The unit is g / 10 minutes.

(7) Optical density (OD) Measured using Macbeth densitometer model TD504. Assuming that the transmission density is D, the incident light amount is Io, and the transmitted light amount is I, D = −log (I / Io).

(8) Glossiness Conforms to JIS-Z8741 (60 ゜ -60 ゜).

(9) Concealing property Concealing property of a film indicates opacity.
When the haze measured according to the TM-D1003-52 method was 90% or more, it was evaluated as ○, when the haze was in the range of 89 to 80%, Δ, and when it was 80% or less, ×.

(10) Printability A corona discharge treatment is applied to the surface of the film, and the surface of the film is treated with a commercially available cellophane printing ink "Cellocolor" ST.
“White” (manufactured by Toyo Ink Mfg. Co., Ltd.) was applied using a coating bar # 5, dried in an oven at 80 ° C. for 1 minute, and then dried.
It was left at 50 ° C. and 50% RH for 24 hours.

a. Cellophane tape peeling test Cellophane tape (Sekisui Chemical Co., Ltd.)
No. 1150, width 24 mm) was adhered and strongly peeled off, and evaluated according to the following five grades based on the ink peeling area.

Ink peeling area 0%: Judgment 5 Ink peeling area less than 10%: Judgment 4 Ink peeling area 10% or more and less than 25%: Judgment 3 Ink peeling area 25% or more and less than 50%: Judgment 2 Ink peeling area 50% or more: Judgment 1 b. Print processing test When 1000 m of the film was gravure-printed, the occurrence of troubles such as ink bleeding, printing deviation, and film wrinkling was evaluated.

(11) Punching test A label punching test was performed on the film at a rate of 100 sheets / minute, and the number of defects such as punching, defects, wrinkles and kinks were evaluated.

(12) Density According to JIS-K6758.

[Example] Hereinafter, an example of the present invention will be described.

Example 1 Polypropylene homopolymer having [η] of 1.85 dl / g and II = 97% (“Mitsui Noblen” FO-8 manufactured by Mitsui Toatsu Chemicals, Inc.)
50) 100 parts by weight and 12 parts by weight of methylpentene homopolymer (“TPX” MX-019, manufactured by Mitsui Petrochemical Co., Ltd., n-heptane extraction residue = 95%, MI = 100 g / 10 minutes) using a Henschel mixer After mixing, the mixture was melt-extruded at 280 ° C. using a 30 mmφ twin-screw extruder to form pellets. The pellets were fed to a 35 mmφ single screw extruder, extruded into a sheet at a resin temperature of 290 ° C. with a T-die, and solidified on a cooling drum kept at 60 ° C.
A polyolefin composition sheet having a thickness of 800 μm was obtained. The sheet was subjected to fine stretching at a magnification of 1.15 times within the elastic limit in the longitudinal direction at 110 ° C. with a roll-type longitudinal stretching machine, and further, 135 ° C. in the longitudinal direction.
After stretching 4.5 times in
Stretched 8 times at 60 ° C, allowing 5% relaxation and 16
Heat treatment was performed at 5 ° C. to obtain a biaxially oriented polyolefin film having a thickness of 20 μm (see Table 1).

When the optical characteristics of the film were examined, the optical density (O
D) is 0.3, and the gloss is 89% for the drum surface and 88 for the non-drum surface.
%, That is, 97% of Bayes has white and excellent concealing properties.

When the mechanical properties of the film were examined, the strength in the longitudinal direction was 12 kg / mm ² , and the sum of the Young's modulus in the longitudinal direction and the width direction was 520 kg / mm ² .

Furthermore, it turns out that this film is excellent in printability. (See Table 2).

Comparative Example 1 The polyolefin composition sheet obtained in the same manner as in Example 1 was stretched in the longitudinal direction at 135 ° C. five times at a time by a conventional sequential biaxial stretching method, and then stretched eight times in the transverse direction at 160 ° C. by a stenter. Thus, a biaxially oriented polyolefin film having a thickness of 20 μm was obtained.
The film has an optical density (OD) of 0.08 and a haze of 68%
And poor whiteness and concealability. (See Tables 1 and 2.) Example 2 Polypropylene homopolymer having [η] of 2.25 dl / g and II = 97% (“Mitsui Noblen” JS-1 manufactured by Mitsui Toatsu Chemicals, Inc.)
429) 100 parts by weight and methylpentene copolymer (“TPX” RT-18, manufactured by Mitsui Petrochemical Co., Ltd., n-heptane extraction residue =
After mixing 18 parts by weight (74%, MI = 26 g / 10 min), the mixture was extruded and solidified in the same manner as in Example 1 to obtain a polyolefin composition sheet having a thickness of 600 μm. The sheet is rolled by a longitudinal stretching machine.
After fine stretching in the longitudinal direction at 100 ° C. at a magnification of 1.20 times within the elastic limit, the film was simultaneously stretched 5 times in both longitudinal and transverse directions at 165 ° C. using a stenter-type simultaneous stretching machine to obtain a film having a thickness of 20 μm. (See Table 1).

The optical aggressiveness (OD) of the film was 0.2, the glossiness was 75% on the drum surface and 72% on the non-drum surface, and the haze was 92%, which was excellent in whiteness and hiding. The longitudinal strength is 10
kg / mm ² , the sum of the Young's modulus in the longitudinal and width directions is 350 kg / mm ²
Met. (See Table 2).

Comparative Example 2 A composition comprising 100 parts by weight of a polypropylene homopolymer (FO-850) and 60 parts by weight of a methylpentene homopolymer (MX-019) was prepared in the same manner as in Example 1, but the film-forming properties were extremely poor. For stability, a film having a thickness of 22 μm was obtained at a fine stretching temperature of 130 ° C., a longitudinal stretching temperature of 140 ° C., and a transverse stretching temperature of 172 ° C. (See Table 1). The film has many internal voids and high optical density (OD) of 0.2, but low gloss of 37%, strength in the longitudinal direction of 6 kg / mm ² , and the sum of the Young's modulus in the longitudinal direction and the width direction is 230 kg / mm. ² and the film edge was sagged during printing, causing printing misalignment. (See Table 2).

Comparative Example 3 A 30 μm thick film was obtained in the same manner as in Example 1 except that a composition containing 100 parts by weight of a polypropylene homopolymer (JS-1429) and 25 parts by weight of calcium carbonate was used. (See Table 1.) It can be seen that the film has high optical density (OD) and haze, and is excellent in whiteness and hiding properties, but is inferior in glossiness and mechanical properties due to a large void volume. (See Table 2).

Claims (2)

(57) [Claims] 1. An optical density (OD) of 0.1 or more and a glossiness of 40%
A white polyolefin film as described above, wherein the strength of the film in the longitudinal direction is 8 kg / mm ² or more, and the sum of the Young's modulus in the longitudinal direction and the width direction is 250 kg / mm ² or more. 2. An isotactic index (II) of 80
%, Polypropylene 100 with intrinsic viscosity of 1.2 to 3.5 dl / g
The resin obtained by adding 5 to 50 parts by weight of a methylpentene polymer whose n-heptane extraction residue is 40% or more to the parts by weight is melt-molded into a sheet or a tube, and then subjected to an elastic limit at a temperature of 120 ° C or less. After fine stretching within 120 ℃
A method for producing a white polyolefin film, wherein the film is stretched at least uniaxially at a temperature of up to 170 ° C.