JPS6140552B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polypropylene multilayer film with improved low-temperature heat-sealability, transparency, slipperiness, and blocking resistance. A biaxially stretched film made of highly crystalline polypropylene is a packaging material with excellent transparency and rigidity, but it cannot be applied to an automatic packaging machine as it is because of its poor heat-sealability. That is, since the heat-sealing temperature of a stretched polypropylene film is usually higher than the stretching temperature, the heat during heat-sealing causes the film to shrink as it attempts to return to its unstretched state, impairing its appearance and reducing its sealing strength. Therefore, multilayer films in which polypropylene films are coated or laminated with various resins having good heat sealability are widely used. Polypropylene multilayer films laminated with polyethylene or ethylene-vinyl acetate copolymers have a low heat-sealing temperature, but they are easily damaged when packaging rice crackers such as rice crackers, which is the main use for polypropylene biaxially stretched films. Therefore, it has the disadvantage of poor scratch resistance, which impairs transparency. It also has the disadvantage of poor blocking resistance, in that the films tend to stick together, making it difficult to open the bag. On the other hand, propylene copolymers made by copolymerizing small amounts of comonomers such as ethylene and butene-1 are widely used because they have high scratch resistance and relatively good blocking resistance. However, the propylene-ethylene copolymer that has been mainly used in the past has had the disadvantage that the heat sealing temperature is 20°C or more higher than that of polyethylene or the like. If the heat-sealing temperature is lowered, the speed at which multilayer films can be made into bags can be increased, which is clearly economically advantageous. Therefore, a resin to be laminated to a polypropylene film is desired to have a low heat-sealing temperature and excellent scratch resistance, blocking properties, and transparency. It is a well-known fact that in order to lower the heat-sealing temperature of propylene copolymers, which have good scratch resistance, it is possible to reduce the crystallinity of the copolymer by increasing the comonomer content in the copolymer. However, propylene copolymers with higher comonomer content are more difficult to produce industrially and therefore more expensive, and the amount of amorphous polymer contained in the copolymer increases, making it difficult to make multilayer films. It had the disadvantage of poor slipperiness and blocking properties, making it difficult to put it into practical use. Conventionally, as a multilayer film with a crystalline propylene copolymer layer with a low heat sealing temperature,
The use of a crystalline propylene random copolymer having a composition of 1 to 10% by weight of a linear α-olefin other than propylene and 0.1 to 4.0% by weight of ethylene has been proposed (Japanese Patent Application Laid-Open No. 11281-1981); The heat seal temperature has not yet decreased sufficiently. It has also been proposed to use a propylene-α-olefin random copolymer containing 5 to 20% by weight of α-olefin having 4 to 10 carbon atoms (Japanese Patent Publication No. 1983-
30434), simply using a copolymer with the above composition would result in poor slipping and blocking properties, so a large amount of lubricant would have to be added, and as a result, the lubricant would bleed onto the film surface and damage the base film. The high transparency, which is a distinguishing feature of axially oriented polypropylene films, is significantly impaired. As a result of extensive research into the causes of such defects, the present inventors discovered that the content of a polymer soluble in xylene at 20°C (hereinafter referred to as cold xylene soluble portion) is the dominant factor. , arrived at the present invention. That is, the present invention provides a crystalline polypropylene layer and a carbon atom having 4 to 18 carbon atoms obtained by a liquid phase heterogeneous polymerization method.
-Crystalline propylene with an olefin content of 10 to 30% by weight, an ethylene content of 0 to 5% by weight, and a content of a polymer soluble in xylene at 20°C of not more than 15% by weight -α-olefin Alternatively, it is a polypropylene multilayer film comprising a crystalline propylene-α-olefin-ethylene copolymer layer. The α-olefin in the crystalline propylene copolymer used in the present invention has 4 to 18 carbon atoms in the molecule.
Specific examples include butene-1, pentene-1, hexene-1, 4-methylpentene-1, 3-methylpentene-1, octene-1, decene-1, dodecene-1, These include tetradecene-1, hexadecene-1, octadecene-1, and the like. One or more types of these may be contained. Butene-1 is particularly preferred as the α-olefin. The α-olefin is contained in the copolymer in an amount of 10 to 30% by weight. If it is less than 10% by weight, the heat sealing temperature will not be lowered sufficiently, which is not preferable. Also 30% by weight
Above this amount, the crystallinity of the copolymer is undesirably reduced. More preferably, the α-olefin content is 25% by weight or less. Ethylene may or may not be contained in the copolymer. If a large amount of ethylene is contained, the scratch resistance deteriorates, so the ethylene content must be 5% by weight or less, preferably 3% by weight or less. The cold xylene soluble portion contained in the copolymer is
For the following reasons, the content is 15% by weight or less, preferably 10% by weight or less, and more preferably 5% by weight or less.
As an example, 0.2% of Sumilizer BHT as an antioxidant, 0.5% of a silica-based anti-blocking agent, and 0.2% of fatty acid amide as a lubricant were added to a propylene-butene-1 copolymer, and a film was formed using a T-die extruder. First, the relationship between the butene-1 content, cold xylene soluble content, and blocking property of a 30μ single-layer film is
As shown in the figure. As can be seen from FIG. 1, the blocking property is slightly affected by the butene-1 content, but the effect of the cold xylene soluble content is more significant. If the amount of anti-blocking agent is increased in a copolymer with a large amount of cold xylene soluble portion, the transparency will be significantly reduced and the film will not be suitable as a packaging film. Furthermore, if the amount of cold xylene soluble portion exceeds a certain level, desired opening properties cannot be obtained even if a large amount of a known anti-blocking agent is added. Similar to the blocking property, the sliding property is greatly influenced by the cold xylene soluble portion. Therefore, it is not possible to obtain an excellent packaging film simply by increasing the comonomer content of the copolymer layer, and it is necessary to use a copolymer with a low content of cold xylene soluble parts. The crystalline propylene copolymer with a high monomer content and a small amount of cold xylene soluble portion used in the present invention is
It can be manufactured by the method previously invented by the present inventors (Japanese Patent Application No. 53-72436, Japanese Patent Application No. 75113-1983, Japanese Patent Application No. 1983-1983)
75837), as mentioned in the specifications of these patent applications, when manufactured by conventional methods, the higher the comonomer content, the more difficult it is to industrially manufacture the crystalline propylene copolymer, and the lower the cold xylene soluble portion. increases significantly. The polypropylene multilayer film of the present invention has crystalline propylene-α-olefin or crystalline propylene-α-olefin-ethylene copolymer with a small amount of cold xylene soluble portion on one or both sides of a crystalline polypropylene film as a base material. It can be obtained by laminating layers by a known method. That is, preformed sheets of the substrate layer and copolymer layer are passed together between pressure rollers using an adhesive, or the copolymer is applied as a solution or dispersion in a solvent such as toluene onto the substrate layer. by melt-extrusion coating the copolymer onto the substrate layer, or by extruding the copolymer and the substrate polymer in separate extruders and extruding them in a common die or exit while both are still molten. The multilayer film of the present invention can be obtained by a method such as bonding. In the multilayer film of the present invention, at least the polypropylene layer is preferably stretched uniaxially or biaxially. Such a polypropylene stretched multilayer film is manufactured by the following known method. In other words, crystalline propylene-α with a small amount of cold xylene soluble portion is added to the crystalline polypropylene sheet serving as the base material.
It can be produced by laminating -olefin or a crystalline propylene-α-olefin-ethylene copolymer and then stretching both at the same time. Methods for laminating a crystalline propylene copolymer onto a crystalline polypropylene sheet serving as a base material include the following methods. (1) A method using so-called simultaneous extrusion or coextrusion, in which both are combined while they are still in a molten state in the extrusion die for forming the sheet or near the exit. (2) A method in which both are formed into a solid sheet and then stacked on top of each other. (3) A base polypropylene sheet is uniaxially stretched in advance in the extrusion direction while being heated with a group of rolls including metal rolls, and the propylene copolymer is laminated onto this sheet in a heated molten state or in a solidified state in the form of a sheet. Method. In order to explain the method of the present invention more clearly, comparative examples and examples are described below, but the present invention is not limited only by these examples.
Note that the characteristic values in the following examples were measured by the following method. (1) Cold xylene soluble part After dissolving 5 g of polymer in 500 ml of boiling xylene, it was slowly cooled to room temperature, left to stand at 20°C for 4 hours to separate the precipitated polymer, and the xylene was evaporated from the liquid, followed by reducing the pressure. The cold xylene soluble polymer was recovered by drying at 60°C. The percentage of the recovered polymer to the sample polymer was defined as cold xylene soluble portion %. (2) Heat sealing temperature The peeling speed of a 25 mm wide sample obtained by pressing the laminated surfaces of the film together using a heat sealer at a specified temperature for 2 seconds under a load of 2 kg/cm ²
The temperature at which the peeling resistance obtained by peeling at 200 mm/min and a peeling angle of 180 was 300 g/25 mm was defined as the heat sealing temperature. (3) Transparency (haze) According to ASTMD 1003. (4) Opening properties (blocking) Test pieces were blocked by treatment at 60° C. for 3 hours under a load of 40 g/cm ² and measured using a blocking tester manufactured by Shimadzu Corporation. (5) Scratch resistance A sample film was pasted on the bottom of a box made of polymethyl methacrylate resin with a length of 13 cm, a width of 11 cm, and a depth of 5 cm, with the laminate surface facing upward.
Fill the box with 100 c.c. of ~25 mesh sea sand, attach this box to a vibrator, and vibrate horizontally for 15 seconds at a frequency of 300 vibrations per minute. The film after the test was washed with water and dried, and the haze was measured according to ASTMD-1003, and the difference from the haze before the scratch resistance test was used as a measure of scratch resistance. Example 1 (i) Production of copolymer Preparation of catalyst 1 Preparation method (preparation of reduction product) After purging a 200-volume reaction vessel with argon, 40% of dry hexane and 10% of titanium tetrachloride were added.
This solution was kept at -5°C, and a solution consisting of 30% of dry hexane and 23.2% of ethylaluminum sesquichloride was added dropwise under such conditions that the temperature of the reaction system was maintained at -3°C or below. Stirring was then continued at the same temperature for 2 hours. After the reaction, the resulting reduced product was allowed to stand still and was subjected to solid-liquid separation at 0°C, and washed twice with 40 kg of hexane to obtain 16 kg of reduced product. 2. Adjustment method The reduction product obtained by the preparation method is slurried in n-decalin, and the slurry concentration is adjusted to
Heat treatment was carried out at 140° C. for 2 hours at a concentration of 0.2 g/cc. After the reaction, the supernatant liquid was extracted and washed twice with 40% hexane to obtain titanium trichloride composition A. 3 Preparation method 11 kg of titanium trichloride composition A prepared according to the preparation method was slurried in ₅₅ toluene, and iodine and Titanium trichloride solid catalyst B was obtained by adding isoamyl ether and reacting at 80° C. for 1 hour. Copolymerization of propylene-α-olefin After replacing the polymerization vessel with an internal volume of 200 with a stirrer sufficiently with propylene, liquefied propylene 32.3
Kg, liquefied butene - 119.1Kg was delivered. Then aluminum diethyl monochloride 50
g, 4 g of the titanium trichloride solid catalyst B and 8 g of methyl methacrylate were introduced into a polymerization vessel, and the temperature was raised to 60°C. During the polymerization, a total of 13 kg of propylene was added to keep the butene-1 concentration in the liquid phase constant. After polymerization for 4 hours, the slurry was placed in n-heptane at 60° C. into which isobutanol had been added in advance, and after treatment for 30 minutes, the solvent containing the amorphous polymer was shaken off. After drying, 23.3 kg of powdered polymer was obtained. (ii) Evaluation The characteristic values of the polymer obtained in (i) were measured and evaluated as follows. An isotactic polypropylene sheet having a melt index of 2.0 was stretched in the longitudinal direction at a ratio of 5 times to obtain a uniaxially stretched sheet having a thickness of 180 μm. On one side of this sheet, a propylene-butene-1 copolymer shown in Table 1 was melt-extruded from a T-die extruder and a 60 μm thick copolymer layer was laminated thereon. The obtained two-layer laminate sheet was stretched in the transverse direction to an effective magnification of 6 times, and subjected to tension heat treatment at 150° C. for 5 seconds to obtain a two-layer laminate film. The properties of this two-layer film are shown in Table 1. Example 2 The same method as Example 1 was carried out except that the polymerization was carried out so that the butene-1 content was 20.5 wt%. The results obtained are shown in Table 1. Example 3 (i) Production of copolymer Preparation of catalyst 1 Preparation method (preparation of reduction product) After purging a 200-volume reaction vessel with argon, 40% of dry hexane, 10% of titanium tetrachloride
This solution was kept at -5°C, and a solution consisting of 30% of dry hexane and 23.2% of ethylaluminum sesquichloride was added dropwise under such conditions that the temperature of the reaction system was maintained at -3°C or lower. Stirring was then continued at the same temperature for 2 hours. After the reaction, the resulting reduced product was allowed to stand still and was subjected to solid-liquid separation at 0°C, and washed twice with 40 kg of hexane to obtain 16 kg of reduced product. 2 Preparation method The reduction product obtained by the preparation method is slurried in n-decalin, and the slurry concentration is adjusted to
Heat treatment was carried out at 140° C. for 2 hours at a concentration of 0.2 g/cc. After the reaction, the supernatant liquid was extracted and washed twice with 40% hexane, and titanium trichloride composition A was extracted.
I got it. 3 Preparation method 11 kg of titanium trichloride composition A prepared according to the preparation method was slurried in ₅₅ toluene, and iodine and Titanium trichloride solid catalyst B was obtained by adding diisoamyl ether and reacting at 80°C for 1 hour. Pretreatment of Catalyst System After purging a reaction vessel with an internal volume of 5 with a stirrer with argon, 11 g of dry n-heptane, 16 g of the above-mentioned titanium trichloride solid catalyst B, and 70 g of aluminum diethyl monochloride were charged.
Next, the inside of the reactor was replaced with propylene and the temperature was lowered.
The temperature was raised to 50°C, and 300g of propylene was fed and reacted with stirring to obtain catalyst system C. Copolymerization of propylene-α-olefin After fully replacing a polymerization vessel with a stirrer with an internal volume of 200 mL with propylene, industrial heptane 68
was sent. The entire amount of the catalyst system C was added and washed with industrial heptane, so that the final amount of industrial heptane was 70. Next, 6 kg of propylene, 3 kg of butene-1, and 70 g of ethylene
The temperature was raised to 50℃ and the gauge pressure was 4.
Kg/ ^cm2 . By strictly controlling the gas phase composition of butene-1, propylene, and ethylene under an appropriate hydrogen partial pressure, 4 kg of butene-1, 1 kg of ethylene, and 25 kg of propylene were continuously fed. After introducing 10% of isobutanol and 70% of industrial heptane into the slurry after polymerization, the temperature is raised to 60°C and post-treatment is performed for 30 minutes. Thereafter, the slurry was separated into a salt core, washed with water, and further vacuum-dried to obtain 31 kg of powdered polymer. (ii) Evaluation The characteristic values of the polymer obtained in this way are shown in Example 1.
Evaluation was made in the same manner as method (ii). The results are also shown in Table 1. Comparative Example 1 (i) Production of copolymer Using the same catalyst as in Example 3, the concentrations of propylene, butene-1 and hydrogen were changed, and isobutanol was added to the slurry after polymerization, followed by washing with water and polymerization. Polymerization was carried out in the same manner as in Example 3 except that the entire amount of the combined product was recovered. (ii) Evaluation The characteristic values of the polymer obtained in this way are shown in Example 1.
Evaluation was made in the same manner as method (ii). The results are also shown in Table 1. Comparative Example 2 (i) Production of copolymer Using the same catalyst as in Example 3, polymerization was carried out in the same manner as in Example 3 except that the propylene, ethylene and hydrogen concentrations were changed, and post-treatment was performed. (ii) Evaluation The characteristic values of the polymer obtained in this way are shown in Example 1.
Evaluation was made in the same manner as method (ii). The results are also shown in Table 1. Example 4 The same isotactic polypropylene and propylene-butene-1 copolymer used in Example 1 were extruded from separate extruders, and a structure was prepared in which the manfold part was separate and joined at the land part. A two-layer sheet is made by co-extrusion using a die, and then sequentially stretched 5 times in the machine direction and 6 times in the transverse direction to form a two-layer film with a polypropylene layer of 30μ and a propylene-butene-1 copolymer layer of 10μ. Obtained. The properties of this two-layer film are shown in Table 1. 【table】

[Brief explanation of the drawing]

Figure 1 shows the relationship between the cold xylene soluble content (wt%) on the horizontal axis and the blocking (g/100cm ² ) of a single layer film on the vertical axis for a crystalline propylene-butene-1 copolymer. It is something. In the figure, white circles (○) indicate butene-1 content of 12±0.5% by weight.
White squares (□) are 15±% by weight, black circles (●) are 20±1
Weight %, open triangles (△) indicate results for 25±1 weight % copolymer.

Claims (1)

[Claims] 1. A crystalline polypropylene layer, the content of α-olefin having 4 to 18 carbon atoms obtained by a liquid phase heterogeneous polymerization method is 10 to 30% by weight, and the content of ethylene is 0 to 5% by weight. %, content of xylene soluble polymer at 20℃
A polypropylene multilayer film comprising a crystalline propylene-α-olefin or crystalline propylene-α-olefin-ethylene copolymer layer containing 15% by weight or less. 2. The multilayer film according to claim 1, wherein the α-olefin is butene-1. 3. The multilayer film according to claim 1 or 2, wherein the content of α-olefin is 10 to 25% by weight. 4. The multilayer film according to claim 1, wherein the ethylene content is 0 to 3% by weight. 5 The content of polymer soluble in xylene at 20℃ is 10
% or less by weight of the multilayer film according to claim 1. 6 The content of polymer soluble in xylene at 20℃ is 5
% or less by weight.