JPS6031672B2 - Polypropylene biaxially stretched composite film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a biaxially oriented polypropylene composite film.

More specifically, the present invention relates to a biaxially stretched polypropylene composite film with improved heat sealability. Biaxially stretched crystalline polypropylene films have excellent mechanical properties such as tensile strength, rigidity, surface hardness, impact strength, and cold resistance.
It is widely used in the field of food packaging because it has excellent optical properties such as gloss and transparency, and food hygiene properties such as non-toxicity and odorlessness.

However, a single layer of biaxially stretched polypropylene composite film cannot be heat-sealed because the film shrinks when heated to a temperature that allows heat-sealing. For this reason, heat-sealability has been improved by using a double-stretched polypropylene composite film as a base material and laminating a resin having a low melting point thereon. The resin used to improve heat-sealability has the following characteristics: 'i) It must be able to be heat-sealed at a much lower temperature than the base material, 'ii) It must have high heat-sealing strength, and other things.'
Side: Good adhesion to the base material, 'M: Transparency equivalent to or better than the base material, M: No blocking during storage, ~i': For bag making, filling and packaging jigs. Performance requirements include non-adhesion, good scratch resistance, and little change in heat seal strength over time.

Up to now, many resins have been proposed for the same purpose, but none of them can fully satisfy the above performance.

For example, high- and low-density polyethylene are difficult to use for the same purpose due to their poor transparency, while ethylene-vinyl acetate copolymers and ethylene-Q-olefin copolymers have excellent blocking and scratch resistance. This is not desirable in some respects. Lamination of ethylene-propylene copolymer has also been proposed in Japanese Patent Publication No. 46-3147 as a material with good scratch resistance, blocking property, and relatively good heat sealing property.
No. 8, Samurai Ko No. 49-14343 and is well known, and among ethylene-propylene copolymers, ethylene-propylene random copolymer has good transparency;
It is also known that the heat sealability is excellent.

However, even with the ethylene-propylene random copolymer proposed in Japanese Patent Publication No. 49-14343,
The appropriate heat-sealing temperature is more than 1000 times higher than medium-high density polyethylene, etc., and improvements in low-temperature and heat-sealing properties are required. Since the heat-sealable temperature of an ethylene-propylene random copolymer decreases in proportion to the ethylene content, it is thought that increasing the ethylene content is sufficient to improve the heat-sealability of a biaxially stretched film. In fact, if the ethylene content of the ethylene-propylene random copolymer exceeds 10 mol%, the scratch resistance and blocking resistance of the film will deteriorate significantly, and ethylene will become difficult to polymerize randomly, resulting in poor transparency. You can only get what you want. Q- other than ethylene
A method of using a copolymer of olefin and propylene as a heat-sealing layer has also been proposed; for example,
Tokukan Sho 50-128781 describes a polymer of propylene and a bar-olefin having 4 to 10 carbon atoms in the molecule, the propylene content being 80% to 95% by weight based on the copolymer. % (84.2% for Q-olefin or 1-butene, 96.2% by mole) as a heat seal layer.

However, as a result of additional tests by the present inventors, the propylene-1-butene polymer polymerized using the titanium trichloride catalyst disclosed in the above-mentioned publication has an appropriate heat-sealing temperature of 130°C.
oo or more, and compared to the previously mentioned ethylene-propylene random copolymer, there was not much improvement in terms of low-temperature heat-sealing properties and changes in heat-sealing properties over time, and it could not be said to be satisfactory. . Even in the case of conventionally known propylene-1-butene copolymers, increasing the ratio of 1-butene, which is an English polymerization component, lowers the melting point and improves low-temperature heat sealability, or on the other hand, the resin becomes sticky. There was a problem with coming. As a result of extensive studies in view of the above points, the present inventors found that if a specific propylene-1-butene random copolymer is used, it has excellent low-temperature heat sealing properties, but has no tackiness or blocking properties. It was discovered that a biaxially stretched polypropylene film could be obtained, and the present invention was achieved. The main object of the present invention is to provide a polypropylene diurethane resin which is superior in low-temperature heat-sealability to conventionally proposed propylene-1-butene copolymers and ethylene-propylene copolymers, and has good blocking resistance. The objective is to obtain an axially stretched composite film.

Another object of the present invention is to obtain a polypropylene double-stretched composite film that has good heat-seal strength and exhibits little change over time. Still another object of the present invention is to obtain a polypropylene Nito stretched composite film with excellent transparency and good scratch resistance. That is, the present invention provides a base material layer consisting of a biaxially oriented isotactic polypropylene layer with a melt index of 0.1 to 100 and a propylene content of 50 to 8.
7 mol%, the heat of crystal fusion based on thermal analysis with a differential scanning calorimeter is 10%, 8 Noule/g, the boiling methyl acetate soluble content is 2.0% by weight or less, and the boiling n-heptane content is 5%. This is a polypropylene double-stretched composite film characterized in that a propylene-1-butene random copolymer layer of .0% by weight or less is laminated thereon.

The polypropylene used in the present invention has a density of 0.89 and 0.92, but a melt index (230°C)
0.1 to 10, isotactic index (
Boiling n-heptane insoluble matter)? 5 to 98% crystalline polypropylene used for two-koji stretched films,
Usually, it is a polymer obtained by polymerizing almost only propylene monomer.

A heat stabilizer, an ultraviolet absorber, an anti-blocking agent, a slip agent, an antistatic agent, etc. can be added to the crystalline polypropylene as necessary to improve its performance as a film. The propylene-1-butene random copolymer that can be used as the heat seal layer in the polypropylene biaxially stretched composite film of the present invention has the following characteristics.

'i} Melt Index (ASTM-D-1238
-65T, 230qC) is 0.1 None, 100, preferably 1 None, 50, {ii- Propylene content 5
0 to 87 mol%, preferably 60 to 85 mol%
, especially 65% and 80% by mole, {iii) Crystal heat of fusion of 10% and 80% Joule/g, preferably 2
0 to 70 Jo mountain e/g, rib boiling methyl acetate solubles 2. % by weight or less, preferably 1. % by weight or less, M
Boiling n-hebutane insoluble content is 5.0% by weight or less, preferably 3.0% by weight or less. weight% or less.

The propylene-1-butene random copolymer used in the present invention must satisfy all of these conditions.

For example, if the melt index of {i is less than 0.1, the moldability will be poor and it will be difficult to obtain a thin layer with 10 peaks or less, which is desirable as a heat seal layer.On the other hand, if it exceeds 100, the heat seal strength will be poor. Inferior. The melting point Tm (°C) of the propylene-1-butene random copolymer used in the present invention is usually in the range of 75 to 14,000, and the melting point Tm (°C) of the copolymer with a propylene content of y mol% is usually 1
．． Low -16mi Tm≦1. A range of 124 hearts, often 1
．． Shinichi lISTm≦1. It is in the range of 119 hearts. Therefore, if the propylene content exceeds 87 mol%, the melting point of the resin will be 14,000 or higher, and the appropriate heat sealing temperature will be 130 qo or higher, which is almost the same as the propylene-1-butene copolymer proposed in the past. not adapted to. On the other hand, a polymer having a propylene content of less than 50 mol % is not preferable because its low-temperature heat-sealability is poor, but its bondability to the base polypropylene is poor, and its scratch resistance is poor. Furthermore, the film undergoes flocking during storage, making it unsuitable for practical use. The heat of fusion of 'iii} is a value that correlates with the crystallinity of the polymer,
The propylene-1-butene random copolymer that can be used in the present invention has lower crystallinity than those prepared using titanium trichloride-based catalysts even at the same propylene content, and therefore can be heat-sealed at lower temperatures. On the other hand, those manufactured using vanadium-based catalysts exhibit almost no heat of crystal fusion;
When such a polymer is used as a heat seal layer,
The scratch resistance and blocking resistance are extremely poor and it cannot be used practically. That is, when the heat of fusion of the propylene-1-butene random copolymer is 10 Jo, e
If the heat of fusion exceeds 80 Joule/g, the degree of crystallinity will increase and it cannot be used due to lack of scratch resistance, tendency to flocculate, and a sticky feel. The sealing performance is comparable to that of propylene-1-butene copolymer, which has been proposed in the past.
Not suitable for the purposes of the present invention.

In particular, a polymer having a heat of fusion in the range of 20 to 70 Joule/g is preferable from the viewpoint of the balance between low-temperature heat sealability and blocking resistance. The heat of fusion of the polymer in the present invention is measured using a differential scanning calorimeter (DSC) using a specific heat curve of the copolymer in a completely melted state (preferably 160°
This is a value calculated using a straight line obtained by directly extrapolating the specific heat curve shown in the range from 0 to 240° C. to the low temperature side as the baseline.

The melting point and heat of fusion are measured under the following measurement conditions.

That is, after leaving the sample at 200qo for 5 minutes,
Cool to -40°C at a rate of 10 min and leave at -40°C for 5 minutes. After that, the temperature was increased to -40 at a heating rate of 20 qo/min.
Measurements are made from °C to 200qo. Boiling n-hebutane insoluble content is one measure of the randomness of a copolymer.

Copolymers proposed for titanium trichloride-based catalysts have a high content insoluble in boiling n-hebutane and generally have poor transparency, but only a few copolymers are used in the present invention, which is one reason for the good transparency. ing. The boiling n-hebutane insoluble content of the copolymer used in the present invention is usually 5.0% by weight or less, preferably 3.0% by weight or less.
% by weight or less, more preferably 2.0% by weight or less. The amount of boiling n-heptane that does not fall off is determined by the following method. That is, a sample strip of about 1 rib x 1 side x 1 leg and glass beads are placed in a cylindrical glass filter (G3), and extracted for one hour using a Soxhlet extractor. In this case, the reflux frequency is approximately once/5 minutes. The weight percent of the insoluble content is determined by weighing the dissolved or undropped content. Boiling methyl acetate soluble content is a measure of the breadth and narrowness of the composition distribution and molecular weight distribution, and conventionally proposed copolymers have a large amount of boiling methyl acetate soluble content, which may be the cause of high surface tackiness (stickiness). It has become.

In the present invention, usually 2. % by weight or less, preferably 1.0% by weight or less, and more preferably 0.5% by weight or less. Quantification of boiling methyl acetate soluble content: 1 skin x 1 rib x 1
A fine specimen about the size of a leg is placed in a cylindrical glass filter and extracted using a Soxhlet extractor for 7 hours with a reflux frequency of about 1 time/5 minutes. The soluble content is determined by drying the extracted residue in a vacuum dryer (vacuum level 10 or less) until it reaches a constant weight. As long as the copolymer used in the present invention has the above-mentioned properties, the copolymer used in the present invention has other Q. Olefins such as ethylene may also be copolymerized.

A propylene-1-butene random copolymer having the above-mentioned properties and having a propylene content of 50 to 87 mol % is, for example, (a) a composite containing at least magnesium, titanium, and halogen; Obtained by random copolymerization of propylene and 1-butene using a catalyst formed from an organometallic compound of a Group 1 to Group 3 metal and a 'c' electron donor.The above electron donor {c Part or all of - is a complex {a
} may be fixed to part or all of the compound {b}, or may be pre-contacted with the organometallic compound {b} prior to use. Particularly preferred is an embodiment in which a part of the electron donor [c} is fixed to the complex 'a}, and the remaining part is used by adding it to the polymerization system as it is or by pre-contacting it with the organometallic compound [b}. be. Using such a catalyst system, a copolymer with less methyl acetate soluble content is obtained. In this case, the electron donor immobilized on the complex 'a} and the electron donor used by directly adding it to the polymerization system or by pre-contacting it with (b') may be the same or different. The propylene-1-butene random copolymer used as the heat-sealing layer of the above-mentioned double-stretched polypropylene composite film of the present invention may contain a heat-resistant stabilizer and an ultraviolet absorber in order to improve the performance as a film. , an anti-blocking agent, a slip agent, an antistatic agent, etc. can be added as necessary.

Furthermore, in order to improve the overwrap packaging properties and the adhesion to metals, etc., part or all of the propylene-1-phthene random copolymer may be modified with an unsaturated carboxylic acid or its anhydride. The polypropylene two-bag stretched composite film of the present invention is a composite film in which the specific propylene-1-butene random copolymer layer described above is laminated on one or both sides of a crystalline biaxially stretched polypropylene film serving as a base material. be.

One side of the polypropylene biaxially stretched composite film serving as the base material may be subjected to corona treatment by a conventional method. The following method can be used to produce the biaxially stretched polypropylene composite film of the present invention.

{1-propylene-1-butene random copolymer,
A method in which crystalline polypropylene is coextruded, layered, and then longitudinally stretched and mechanically stretched separately or simultaneously.

■ The base material, crystalline polypropylene, is extruded in a molten state, stretched further in either the longitudinal or machine axis direction, and then the propylene-1-butene random copolymer is extruded in the molten state, or the solidified film is stretched. A method in which the materials are laminated in the same state and then stretched in the perpendicular direction. '3} After extruding the base material crystalline polypropylene in a molten state and subjecting it to longitudinal and transverse stretching separately or simultaneously, a propylene-1-butene random copolymer is placed in a molten state on this biaxially stretched film. A method of extrusion or lamination in a solidified film state.

Among the above three methods, it is preferable to employ method (2) from the viewpoint of ease of molding and stability of film quality.

{In the method of 1', 2, the stretching in the perpendicular direction is carried out at a temperature higher than the melting point of the composition and higher than the melting point of the crystalline material and lower than the melting point of the crystalline polypropylene, or after stretching, heat treatment is performed at the above temperature to form a propylene-1-butene random copolymer. It is preferable to leave the layer in an unstretched state because this improves the transparency and heat sealability of the film. The crystalline polypropylene layer which is the base layer of the biaxially stretched polypropylene composite film of the present invention is 3 to 7 times, preferably 4 to 6 times, in the machine direction, and 3 to 12 times, preferably 12 times, in the transverse direction. 6 is missing, and 1 part is stretched.

In addition, the crystalline polypropylene layer has a thickness of 5 to 200 layers,
Preferably it is in the range of 10 to 60, and the propylene-1-butene random copolymer layer has a molecular weight of 2 to 100.
1, preferably in the range of 3 to 30r. The polypropylene biaxially stretched composite film according to the present invention has better heat-sealability than conventional films, so it can be heat-sealed at lower temperatures.

Therefore, heat sealing is possible over a wide temperature range, and problems caused by poor sealing are alleviated. The film also maintains high levels of transparency, scratch resistance, blocking resistance, and heat seal strength. The polypropylene biaxially stretched composite film of the present invention is suitable for uses such as food packaging, clothing packaging, and textile packaging.

Next, the polypropylene biaxially stretched composite film of the present invention will be specifically explained with reference to Examples.

The haze, heat-seal adhesive strength, blocking resistance, and scratch resistance of the Nimari-stretched composite film were measured by the following methods. '1} Haze Measured by the method of ASTM-D-1003.

■ Heat seal adhesive strength Propylene-1 of polypropylene biaxially stretched composite film
-Place the surfaces on which the butene random copolymers are laminated, 90oo, 10000, 110qo, 120
Temperatures of 00, 130qo and 14030, 2k9/c
After heat-sealing the inner 5 skin of the seal bar for 1 second using vertebra pressure, it was allowed to cool.

15 test pieces were cut out from this sample, and the strength was shown when the heat-sealed portion was peeled off at a crosshead speed of 200 Yanagi/mjn. '3' Change in heat-sealing adhesive strength over time Molded polypropylene double-stretched composite film
After being left at 0 for one week, heat sealing was performed using the method of '2}, and the peel strength was measured.

{4) Blocking resistance Measured by the method of ASTM-D-1893.

[5' Scratch resistance] Layer "exposed kraft paper" without sizing the surface so that it hits the heat sealing surface,
The appearance of scratches after rubbing together at a speed of 50 m/min using a 500 mm iron block as a load was visually judged.

Example 1 [Manufacture of copolymer] In a polymerization vessel made of stainless steel and equipped with a cypress machine, anhydrous magnesium chloride of 200 mm was added as a catalyst component {a},
46' of ethyl benzoate and 30' of methylpolysiloxane were ball milled in a nitrogen atmosphere, then suspended in titanium tetrachloride and heated in a furnace until the titanium concentration was 0.
．． Triethylaluminum 'b} was added to the polymerization vessel so that the concentration was 1.0 mmol/so, and p-methyl toluate was added as the electron donor [c-] to the polymerization vessel so that the concentration in the polymerization vessel was 1.0 mmol/so. A mixed gas of propylene and 1-butene (propylene 55 mol%
, 45 mol % of 1-phthene) was fed at a rate of K per hour to carry out the copolymerization reaction at 70 q○.

The propylene content of the thus obtained propylene-1-butene random copolymer measured by nuclear magnetic resonance spectroscopy was 66.5 mol%, melting point 10,600, heat of fusion 4 ole/g, and melt index 2. 09 boiling n-hebutane insoluble content was 0.5% and boiling methyl acetate soluble content was 0.4%. [Formation of biaxially stretched composite film] After blending a phenolic stabilizer with the propylene-1-butene random copolymer obtained by the above method, 210q
It was granulated at o.

Next, the obtained pellet was heated to 200°C in a press molding machine for 10
The mixture was heated and melted for a minute to form a sheet with a thickness of 0.2 mm. On the other hand, a sheet having a thickness of 0.8 skin was formed using a press molding machine using the same method using a propylene homopolymer having an isotactic index of 96% and a melt index of 1.5.

140q so that no air bubbles remain at the interface between these two sheets.
After stacking the sheet at o to make one sheet, it was stretched to 5 times in length and width at 155°C to 158qo using a simultaneous two-mouse stretching device (manufactured by Toyo Seiki), and then cooled while substantially maintaining this stretched state. did. By the above method, the thickness of the base material layer is approximately 30 mm.
A composite film with a heat-sealing layer thickness of about 6 mm was obtained. Example 2 In the production of the copolymer of Example 1, the mixing ratio of the mixed gas of propylene and 1-butene was changed, resulting in a propylene content of 84.5 mol%, a melting point of 136°C,
Heat of fusion 75 Jo mountain e/g, melt index 0.7
Example 1 was carried out in the same manner as in Example 1, except that a propylene-1-butene random copolymer having a boiling n-hebutane insoluble content of 0.9% and a boiling methyl acetate soluble content of 0.2% was used.

The evaluation results are shown in Table 1. Example 3 In the production of the copolymer of Example 1, propylene and 1-
Propylene content 77.0 mol%, melting point 120°C, heat of fusion 56% obtained by changing the mixing ratio of the butene gas mixture
Same as Example 1 except that a propylene-1-butene random copolymer with Joyama e/g, melt index 2.7, boiling n-hebutane insoluble content 0.6%, and boiling methyl acetate soluble content 0.3 was used. I did the same.

The results are shown in Table 1. Example 4 In the production of the copolymer of Example 1, propylene and 1-
Propylene content 72.5 mol%, melting point 115 do, heat of fusion 5 oul obtained by changing the mixed gas ratio of butene
Example 1 except that a propylene-1-butene random copolymer with e/g, melt index 0.91, boiling n-hebutane uncontainable content 0.5%, and boiling methyl acetate soluble content 0.35% was used. I did the same thing.

The results are shown in Table 1. Example 5 In the production of the copolymer of Example 1, the propylene content was 55 mol%, the melting point was 85 oo, and the heat of fusion was 28 Jou, obtained by changing the mixing ratio of the mixed gas of propylene and 1-butene.
Other than using a propylene-1-butene random copolymer with a melt index of 2.9, a boiling n-heptane insoluble content of 0.3%, a boiling methyl acetate soluble content of 0.34%, and a stretching temperature of 720. was carried out in the same manner as in Example 1.

The results are shown in Table 1. Comparative Example 1 In the production of the copolymer of Example 1, the propylene content was 93 mol%, the melting point was 147 q0, the heat of fusion was 97 Jo mountain e/g, and the mer Index 1.23, boiling n-heptane insoluble content 13.6%
, boiling methyl acetate soluble ~0.15% propylene-1
The same procedure as in Example 1 was carried out except that the -butene random copolymer was used.

The results are shown in Table 1. Comparative Example 2 In the production of the copolymer of Example 1, the propylene content was 48 mol%, the melting point was 74, and the heat of fusion was 17 Jou.
Example except that a propylene-1-butene random copolymer layer with le/g, melt index 3.2, boiling n-hebutane insoluble content 0.3%, and boiling methyl acetate soluble content 0.65% was used. This was done in the same manner as in step 1.

The results are shown in Method 1. Table 1 Example 6 In the production of the copolymer of Example 1, n was used as the polymerization solvent.
- Propylene content: 66.5 mol%, melting point: 10
A propylene-1-butene random copolymer was prepared at 4°C, with a heat of fusion of 3 ole/g, a melt index of 0.90, a boiling n-hebutane insoluble content of 0.30%, and a boiling methyl acetate soluble content of 0.18%. The same procedure as in Example 1 was carried out except for using.

The results are shown in Table 2. Example 7 In the production of the copolymer of Example 1, dimethyl ether was used in place of methyl p-toluate at a rate of 1.0 mmol/g as the electron donor {c) which is a component of the polymerization catalyst, and Propylene content 6 obtained in the same manner except for changing the mixing ratio of propylene and 1-butene in the feed gas
6.5 mol%, melting point 106°C, heat of fusion 30 Jo mountain e/
Example 1 except that a propylene-1-butene random copolymer having a melt index of 5.0, a boiling n-hebutane insoluble content of 0.3%, and a boiling methyl acetate soluble content of 0.6% was used.
I did the same thing.

The results are shown in Table 2. Comparative Example 3 In the production of the copolymer of Example 1, as a polymerization catalyst,
In place of {a}, {b}, 'c-components, titanium trichloride was supplied so that the titanium concentration in the polymerization vessel was 5 mmol/unit, and diethylaluminium monochloride was supplied at 50 mmol/unit. Propylene content 84.2 mol%, melting point (9500 and 1420
0), except that a propylene-1-butene random copolymer with a heat of fusion of 7 ole/g, a melt index of 12, a boiling n-hebutane insoluble content of 28%, and a boiling methyl acetate soluble content of 2.4% was used. The same procedure as in Example 1 was carried out.

The results are shown in Table 2. Comparative Example 4 A copolymer was produced in the same manner as in Example 1 except that vanadium oxytrichloride was added as a polymerization catalyst at a ratio of 4 mmol and diethylaluminum monochloride was added at a ratio of 35 mmol. Propylene content 66.5 mol%, melting point, not observed, heat of fusion O Joule/g, melt index 2.5 boiling n-heptane insolubles 0%, boiling methyl acetate solubles 0.
The same procedure as in Example 1 was carried out except that 5% propylene-1-butene random copolymer was used.

The results are shown in Table 2. Comparative Example 5 Propylene-ethylene block copolymer produced using the catalyst of Example 1 (
The same procedure as in Example 1 was carried out except that ethylene content (20 mol%) was used in the heat seal layer.

The results are shown in Table 2. Comparative Example 6 Propylene-ethylene random copolymer polymerized using the same catalyst as in Example 1 (propylene content 94 mol%, melting point 15200, heat of fusion 10 ode/g, melt index 0.55 boiling n-hebutane) 68% non-falling content, 0.6% boiling methyl acetate soluble content), and the stretching temperature was 1.
The same procedure as in Example 1 was carried out except that the concentration was 35 qo.

Claims (1)

[Scope of Claims] 1. On at least one side of a base material layer consisting of a biaxially stretched isotactic polypropylene layer, a melt index of 0.1 to 100, a propylene content of 50 to 87 mol%, and a differential scanning calorific value. Propylene-1-, which has a heat of crystal fusion of 10 to 80 Joule/g based on thermal analysis using a meter, a boiling methyl acetate soluble content of 2.0% by weight or less, and a boiling n-heptane insoluble content of 5.0% by weight or less. A biaxially stretched polypropylene composite film characterized by laminated with butene random copolymer layers. 2. The film according to claim 1, wherein the propylene content of the propylene-1-butene random copolymer is in the range of 60 to 85 mol%. 3. The film according to claim 1, wherein the propylene-1-butene random copolymer has a heat of crystal fusion in the range of 20 to 70 Joule/g. 4. The film according to claim 1, wherein the propylene-1-butene random copolymer has a boiling methyl acetate soluble content of 1.0% by weight or less. 5. The film according to claim 1, wherein the propylene-1-butene random copolymer has an insoluble content in boiling n-heptane of 3.0% by weight or less.