JP3139510B2 - White biaxially oriented polyolefin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white biaxially oriented polyolefin film. More specifically, the present invention relates to a white biaxially oriented polyolefin film which is white, has a high optical density, is excellent in concealing properties, is excellent in impact resistance and water vapor barrier properties, and has heat sealing properties.

[0002]

2. Description of the Related Art Conventionally, as a white biaxially stretched polyolefin film, an inorganic filler such as calcium carbonate or an incompatible resin such as polyester is blended and stretched, and whitening is performed by light scattering of formed voids. Are known (Japanese Patent Publication No. 60-37793,
No. 1-157547).

[0003]

However, when a large amount of an inorganic filler such as calcium carbonate or an incompatible resin such as polyester is added to a polyolefin to form a whitening film, the volume of voids is large, Is poor in impact resistance and water vapor barrier properties due to its high moisture absorption, and further has the problem of delamination of the surface layer and decrease in whiteness over time. It is not preferable when used as a tape or various wrapping papers.

Accordingly, the present invention has been intensively studied to solve the problems of the above-mentioned white biaxially stretched polyolefin film, and as a result, it is white, has a high optical density, has excellent concealing properties, and has excellent impact resistance and water vapor barrier properties. It also has heat sealing properties, various printing papers, various labels, various adhesive tapes,
An object of the present invention is to provide a white biaxially oriented polyolefin film suitable for various wrapping papers.

[0005]

According to the present invention, there is provided a polymer comprising 65 to 93% by weight of a crystalline polypropylene, 5 to 20% by weight of a thermoplastic resin incompatible with the crystalline polypropylene and having a heat deformation temperature of 120 ° C. or more. 2 to 15% by weight of a resin compatible with the crystalline polypropylene and having a melting temperature of 140 ° C. or lower (provided that polyether ester amide is not contained).
There), optical density in the film thickness 30 [mu] m 0.3
The present invention relates to a white biaxially stretched polyolefin film characterized by having a molecular weight of 5 or more.

The crystalline polypropylene of the present invention (hereinafter referred to as PP)
) Has an intrinsic viscosity [η] of 1.4 to 3.2 dl.
/ G, preferably 1.6 to 2.4 dl / g, an isotactic index (II) of 95% or more, and a melt flow index (MFI) of 1.0 to 15 g / 10 min. It is preferable because various properties such as impact properties and uniformity of optical density are improved. A small amount of a second component other than propylene, for example, ethylene, butene, hexene, etc., may be randomly copolymerized. Further, known additives such as a crystal nucleating agent, an antioxidant, a heat stabilizer, a sliding agent, an antistatic agent, an antiblocking agent, a filler, a viscosity modifier, and a coloring inhibitor may be contained.

The heat distortion temperature (measured according to ASTM D648, load of 4.6 kg / cm ² ) of the thermoplastic resin incompatible with the PP of the present invention must be 120 ° C. or higher, and is preferably 130-180 ° C. When the heat deformation temperature is lower than 120 ° C., void formation by the incompatible resin is insufficient, and it becomes difficult to develop the concealing property, which is not preferable.

As the incompatible resin, specifically, Poly-4
-Methylpentene 1, poly-3-methylbutene 1, polyethylene terephthalate, polybutylene terephthalate, polyamide and the like. Among them, a polycarbonate resin (hereinafter abbreviated as PC) having a weight average molecular weight (hereinafter abbreviated as Mw) of 40,000 or less is preferable because of good dispersibility with PP and excellent chemical stability.

The PC of the present invention is an aromatic polycarbonate, and linear and branched polycarbonates can also be used. The PC may be a homopolymer or a copolymer with other monomers. The heat distortion temperature of the PC is 120 ° C. or higher, preferably 130 ° C. or higher.
If the heat deformation temperature is lower than 120 ° C., void formation is insufficient, and it becomes difficult to develop concealing properties, which is not preferable.
Further, the Mw of the PC of the present invention is preferably 40000 or less. When Mw exceeds 40,000, dispersibility in the PP deteriorates, optical density unevenness occurs, and concealment becomes insufficient.
The impact resistance and the water vapor barrier property are also deteriorated, which is not preferable. Further, it is preferable that the melt flow index is 1 to 50 g / 10 min as the melting property because the dispersibility in the PP is good and the optical density is high.

[0010] The content of the incompatible resin contained in the film of the present invention needs to be 5 to 20% by weight, particularly preferably 10 to 15% by weight. When the content of the incompatible resin is less than the range of the present invention, the whiteness and optical density of the film become insufficient. If the ratio exceeds this range, the impact resistance and the water vapor barrier property of the film of the present invention are deteriorated.

The resin having a melting temperature of 140 ° C. or less, which is compatible with the PP contained in the film of the present invention, is ethylene-α
-One or more resins selected from olefin copolymers and ethylene-α, β-unsaturated carboxylic acid ester copolymers. Among them, ethylene-α-olefin copolymers include ethylene-propylene random copolymer (hereinafter abbreviated as EPC), ethylene-α,
As the β-unsaturated carboxylic acid ester copolymer, ethylene-acrylic acid ester copolymer finely disperses the PC in the PP to improve the concealing property, and further improves the impact resistance and the water vapor barrier property. preferable. In addition, the EPC
And an ethylene-acrylate copolymer having a melt flow index (MFI) of 1.0 to 20 g / 1.
A range of 0 minutes is preferable because mechanical properties, various physical properties such as impact resistance, and uniformity of optical density are improved.

The melting temperature of the resin compatible with the PP contained in the film of the present invention must be 140 ° C. or lower. If the temperature exceeds 140 ° C., the dispersibility of the PC in the PP deteriorates, resulting in poor film-forming stability, and also deteriorates impact resistance and water vapor barrier property.

The content of the resin having a melting temperature of 140 ° C. or less which is compatible with the PP contained in the film of the present invention is 2 to 2.
It is necessary that the content be 15% by weight, and particularly preferably 5 to 10% by weight. When the content of the compatible resin is less than 2% by weight, impact resistance and water vapor barrier properties are deteriorated.
If the ratio exceeds this range, the optical density of the film becomes insufficient.

Although the thickness of the film of the present invention is not particularly limited, it is preferably 10 to 100 μm, more preferably 20 to 70 μm.

The film of the present invention has a film thickness of 30 μm.
The optical density (OD) at m is 0.35 or more, preferably 0.45 or more. When it is less than 0.35, for example, when used as a packaging film, it is insufficient to conceal the contents to be packaged, and when laminated with other base materials such as paper, the surface of the base material becomes transparent. It is not preferable because it becomes easier.

Further, the sum of the Charpy impact strength in the length direction and the width direction of the film of the present invention is 15 (kg · cm / m
m ² ) or more. If it is less than the range of the present invention, it cannot be put to practical use, for example, when used as a base material of a wrapping paper or an adhesive tape.

The water vapor transmission rate of the film of the present invention is desirably 4.0 (g / m ² · day / 0.1 mm) or less. If it is less than the range of the present invention, when it is used for packaging small confectionery or rice confectionery having a high hygroscopicity, the long-term storage property is poor.

Next, the resin of the layer B of the film of the present invention is:
Ethylene-α-olefin copolymer, ethylene-α, β
-It is composed of one or more resins selected from unsaturated carboxylic acid ester copolymers. E among them
PC is preferred because it has a high heat sealing force and a high water vapor barrier property.

The laminated structure of the film of the present invention in which the B layers are laminated is B layer / A layer and B layer / A layer / B layer. The layer thickness of the layer B is preferably 2 to 10 μm.

The film of the present invention can be used for packaging, labeling, adhesive tape, and carding with its own film. Also, it can be used by laminating with paper, polyester film, polypropylene film, aluminum foil and the like. In this case, it is preferable to perform a corona discharge treatment on the surface of the layer B in order to improve the adhesiveness. A known method can be used for the corona discharge treatment, but air, carbon dioxide, nitrogen gas, or carbon dioxide / nitrogen gas is preferable as the atmosphere gas at the time of the treatment, and air is particularly preferred in terms of simplicity and economy. preferable.

Next, the method for producing the white polyolefin film of the present invention will be described, but the present invention is not limited thereto.

A layer resin consisting of a mixture of crystalline PP, an incompatible resin having a heat distortion temperature of 120 ° C. or higher and a compatible resin having a melting temperature of 140 ° C. or lower is supplied to an extruder. Above, preferably 280 ° C to 300 ° C
And extruded into a sheet with a T-type die, and the sheet is wound around a drum at a temperature of 20 to 100 ° C, preferably 40 to 80 ° C, and cooled and solidified. Next, the sheet is stretched 4 to 6 times in the longitudinal direction between rolls having a peripheral speed difference heated to a temperature of 90 ° C. to 130 ° C., and immediately cooled to room temperature. The stretching temperature at this time is preferably a lower limit temperature at which the next transverse stretching property is not deteriorated, and a range of 100 to 120 ° C. because the optical density of the film becomes high. The stretched film is guided to a tenter, stretched 5 to 10 times in the width direction at a temperature of 150 to 165 ° C., and then heat-set at a temperature of 160 to 170 ° C. while giving a 2 to 20% relaxation in the width direction. And wind it up.

The film stretching method of the present invention is preferably a sequential biaxial stretching method, and a simultaneous biaxial stretching method is not preferred because the optical density is hardly increased.

The layer B is laminated by feeding the resin of the layer B to another extruder, melting the resin at a temperature of 220 to 280 ° C., and then using a multilayer molding die to form the layer B / layer A or layer B / layer B. Layer A / B
After merging in a die so as to form a layer, it is formed into a laminated sheet. Further, as another laminating method, after the A-layer resin and the B-layer resin are merged in a short pipe upstream of the die, they are formed into a sheet shape with a T-type die, or in the longitudinal direction in the film forming step. A method is used in which the resin of layer B is extrusion-laminated on the stretched stretched film, the laminated film is guided to a tenter, and stretched in the width direction. In particular,
The resin of the layer B is supplied to an extruder and melted at a temperature of 240 to 260 ° C., and then extruded into a sheet by a crow mouth-type die, and the molten sheet is cooled at a temperature of 5 to 50 ° C. And a rubber roll, and a film stretched in the longitudinal direction is bonded and pressed.

The film of the present invention may be added or coated with additives such as an antistatic agent, a weathering agent, an anti-fogging agent and a slipping agent according to the purpose. Further, a known treatment such as a corona discharge treatment may be performed in an air atmosphere, an inert gas atmosphere, or the like for the purpose of surface modification.

Further, the film of the present invention can be used by embossing, printing, extrusion lamination, laminating with other resin films, paper, cloth, etc., according to the purpose.

[0027]

[Method for measuring characteristics and method for evaluating effects] The method for measuring characteristic values and the method for evaluating effects according to the present invention are as follows.

(1) Intrinsic Viscosity ([η]) 0.1 g of a sample was completely dissolved in 100 ml of tetralin at 135 ° C., and this solution was measured in a thermostat at 135 ° C. with a viscometer. Determine the intrinsic viscosity according to the formula. The unit is dl / g. [Η] = S / 0.1 × (1 + 0.22 × S)

(2) Isotactic index (I
I) Vacuum dry the sample at 130 ° C for 2 hours. From now on weight W
Take (mg) sample, place in Soxhlet extractor and extract with boiling n-heptane for 12 hours. Next, the sample is taken out, sufficiently washed with acetone, vacuum-dried at 130 ° C. for 6 hours, and then the weight W ′ (mg) is measured and determined by the following equation. II (%) = W ′ / W × 100

(3) Film thickness The film thickness was measured using a dial gauge type thickness gauge (JIS-B-7509, measuring element 5 mmφ flat type).

(4) Charpy impact strength A value obtained by a Charpy impact tester, and energy E (kg · cm) required in the direction of cutting the test piece.
Is divided by the sample width (cm), and the calculation method is as follows. E = WR (cos β-cos α) W is the hammer weight (kg), R is the distance (cm) from the rotation center axis of the hammer to the center of gravity, α is the hammer lifting angle, and β is the hammer swing angle after cutting the test piece. . The measurement atmosphere is 25 ° C./65% RH.

(5) Optical density (OD) The optical density (OD) was measured using a densitometer TD-504 manufactured by Macbeth. Assuming that the incident light amount is I0 and the transmitted light amount is I, OD = -log (I / I0). The value obtained by converting this value into a film thickness of 30 μm is described.

(6) Melting temperature (Tm) and melt crystallization temperature (Tmc) Using a differential scanning calorimeter (DSC-2, manufactured by PerkinElmer), 5 mg of a sample was heated from room temperature to 20 ° C./min. The melting endothermic peak accompanying the melting of the crystal when the temperature is increased at a rate is defined as the melting temperature (Tm). Then 280 ° C
The temperature was raised to the melting holding temperature of
During cooling at a cooling rate of / min, the peak temperature of latent heat accompanying crystallization was defined as the melt crystallization temperature (Tmc).

(7) Weight average molecular weight (Mw) The weight average molecular weight (Mw) was determined under the following measurement conditions. Apparatus: HLC A802 type manufactured by Tosoh Corporation Column: GMH6 × 2, G2000H8 manufactured by Tosoh Solvent: tetrahydrofuran Temperature: 23 ° C Flow rate: 1.5 ml / min

(8) Melt flow index (MF)
I) According to ASTM-D-1238, PP and a resin compatible with the PP are 230 ° C, 2.16 kg, and PC is 300
The measurement was performed at 1.2 ° C. and 1.2 kg.

(9) Thermal deformation temperature of resin Load of 4.6 kg according to the method of ASTM-D-648.
/ Cm ² was determined as the heat distortion temperature.

(10) Heat sealing force The adhesive layers of the films are superimposed on each other and put between a metal plate and silicon rubber heated at 120 ° C. and a pressure of 1 k
Heat sealing was performed under the conditions of g / cm ² and 1 sec, and the strength at the time of peeling 90 ° at a peeling speed of 300 mm / min was measured.

(11) Delamination of the film surface A cellophane tape (NO405, manufactured by Nichiban Co., Ltd.) having a length of 50 mm was stuck on the film surface, and the film was manually peeled (speed: about 200 mm / sec). Was determined based on the presence or absence of cleavage of the surface layer portion.

(12) Water vapor transmission rate A value measured in accordance with JIS Z-0208 under the conditions of 40 ° C. and 90% RH, and is expressed in g / m ² · day / 0.1 mm.

[0040]

EXAMPLES The present invention will be described based on examples and comparative examples.

Examples 1-3, Comparative Examples 1-4 Crystalline PP (Intrinsic viscosity: 1.80 dl / g, MI: 4.
0 g / 10 min, II: 97%) resin and PC (thermal deformation temperature: 138 ° C.) as an incompatible resin with the crystalline PP,
First, ethylene-methacrylic acid copolymer (EMA) is used as a resin compatible with the crystalline PP and having a melting temperature of 100 ° C.
The mixture was mixed in the proportions shown in the table and supplied to an extruder, melted at a temperature of 290 ° C., guided to a T-type die and extruded into a sheet.
It was wound around a drum at a temperature of 60 ° C. and cooled and solidified into a sheet. After the sheet was preheated by passing through a roll maintained at 110 ° C, it was stretched 5.0 times in the longitudinal direction between rolls having different peripheral speeds at a temperature of 125 ° C, and immediately cooled to 40 ° C. Next, the stretched sheet is guided to a tenter, preheated to a temperature of 165 ° C, stretched 10 times in the width direction at a temperature of 155 ° C, and then 165 ° C while giving 5% relaxation in the width direction.
, And then cooled and wound up. The film characteristics were as shown in Table 2. Films in the range of the present invention had high optical density, excellent concealing properties, and excellent impact resistance and water vapor barrier properties. Films out of the range of the present invention were inferior in any of optical density, impact resistance, and water vapor barrier properties, and the films aimed at by the present invention could not be obtained.

Examples 4 and 5 and Comparative Examples 6 and 7 In Example 4, the incompatible resin of Example 1 was polyphenylene oxide (PPO) (thermal deformation temperature: 132 ° C.), and the compatible resin was ethylene-methacrylic. Methyl acid copolymer (EMMA) (melting temperature: 110 ° C.), and in Example 5, the compatible resin was EPC having an ethylene content of 4.5 wt%.
(Melting temperature: 132 ° C.), and in Comparative Example 6, Example 1
Polystyrene (PS) (thermal deformation temperature:
78 ° C.), and in Comparative Example 7, the compatible resin of Example 1 was replaced with EPC having an ethylene content of 2 wt% (melting temperature: 147).
C) except that the film was manufactured in the same manner as in Example 1. The film characteristics were as shown in Table 2. The film in which the incompatible resin has a heat distortion temperature in the range of the present invention has a high optical density and excellent concealing properties, and has excellent impact resistance and water vapor barrier properties. , Optical density, impact resistance, and water vapor barrier properties were inferior, and the film aimed at by the present invention could not be obtained.

Examples 6 and 7 In Example 6, EPC having an ethylene content of 3.7 wt% was used as the resin of the resin composition (layer A) of Example 1 and the resin of layer B.
In Example 7, EMA having a methacrylic acid content of 10 wt% was used.
Are supplied to two separate extruders, respectively, so that the A-layer resin is melted at a temperature of 280 ° C. and the B-layer resin is melted at a temperature of 260 ° C. so as to be B-layer / A-layer / B-layer with a multilayer molding die. After merging in the die, a biaxially stretched composite film was produced in exactly the same manner as in Example 1. As shown in Table 2, the film characteristics are high in optical density and excellent in concealing properties, excellent in impact resistance and water vapor barrier properties, and there is no delamination between A layer / B layer and high heat sealing force. Was something.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

As described above, the white biaxially stretched polyolefin film of the present invention is a film obtained by successively biaxially stretching a resin obtained by adding a specific incompatible resin and a compatible resin to crystalline PP. Thus, the following excellent effects are produced.

(1) It is white and excellent in concealing property, and the printed undercoat layer can be omitted, resulting in good print finish. (2) It has excellent mechanical strength and impact resistance required for secondary processing, and has good properties for various printing papers and adhesive tape bases. (3) Since the shape of the void is small and flat and uniform, it is excellent in the moisture-proof property required for packaging confectionery and snacks. (4) Since no inorganic particles are added, the film is excellent in film forming properties.

Of the front page Continued (51) Int.Cl. ⁷ identification mark FI C08L 23:16 33:10 (56) Reference Patent flat 4-122736 (JP, A) (58 ) investigated the field (Int.Cl. ⁷ , DB name) C08J 5/18 B29C 55/12

Claims (4)

(57) [Claims] 1. 65 to 93% by weight of crystalline polypropylene
5 to 20% by weight of a thermoplastic resin incompatible with the crystalline polypropylene and having a heat deformation temperature of 120 ° C. or more, and 2 to 15% by weight of a resin compatible with the crystalline polypropylene and having a melting temperature of 140 ° C. or less. Consisting of (but polyether
Does not contain ester amide) , film thickness 30 μm
Wherein the optical density is 0.35 or more. 2. The thermoplastic resin according to claim 1, wherein the thermoplastic resin incompatible with the crystalline polypropylene and having a heat distortion temperature of 120 ° C. or more is a polycarbonate resin having a weight average molecular weight (MW) of 40,000 or less. White biaxially oriented polyolefin film. 3. A resin compatible with crystalline polypropylene and having a melting temperature of 140 ° C. or lower is selected from ethylene-α-olefin and ethylene-α, β-unsaturated carboxylic acid ester copolymers. The white biaxially stretched polyolefin film according to claim 1, which is the above resin. 4. The white biaxially stretched polyolefin film (A layer) according to claim 1, wherein at least one surface of the white biaxially stretched polyolefin film comprises an ethylene-α-olefin copolymer or an ethylene-α, β-unsaturated carboxylic acid ester copolymer. A white biaxially stretched polyolefin film, comprising a resin layer (layer B) composed of one or more selected resins.