JPS6125546B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to polypropylene composite films. More specifically, the present invention relates to a polypropylene composite film with improved heat sealability. Crystalline polypropylene film has tensile strength,
It is popular in the food packaging field due to its excellent mechanical properties such as rigidity, surface hardness, impact strength, and cold resistance, optical properties such as gloss and transparency, and food hygiene properties such as non-toxicity and odorlessness. widely used. However, when a single layer of polypropylene film is used, the temperature at which it can be heat-sealed is high, and the appropriate temperature range is narrow, so that problems such as poor welding or melting of the heat-sealed portion tend to occur. For this reason, heat sealability has been improved by using a polypropylene film as a base material and laminating a resin having a low melting point thereon. The resin used to improve heat-sealability must (i) be able to be heat-sealed at a much lower temperature than the base material, (ii) have high heat-seal strength, and (iii) be able to bond well with the base material. Good adhesion; (iv) Transparency equal to or greater than that of the base material; (v) No blocking during storage; (vi) No adhesion to bag making, filling and packaging jigs. , (vii) good scratch resistance, and (viii) 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 polyethylenes are difficult to use for the same purpose due to their poor transparency and poor adhesion to substrates, while ethylene-vinyl acetate copolymers and ethylene-α-olefin copolymers Coalescence is unfavorable from the standpoint of blocking and scratch resistance. It is also known that ethylene-propylene copolymers are laminated as they have good scratch resistance, blocking properties, and relatively good heat-sealability. Among ethylene-propylene copolymers, ethylene-propylene random copolymers It is also known that the polymer has good transparency and relatively good heat sealability. However, for example, ethylene
Even for propylene random copolymers, the appropriate heat-sealing temperature is more than 10°C higher than that of medium-high density polyethylene, etc., and improvements in low-temperature and heat-sealing properties are required. Since the heat-sealable temperature of 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 the film, but in reality ethylene-
The ethylene content of propylene random copolymer is
If the amount exceeds 10 mol %, the scratch resistance and blocking resistance of the film will be significantly deteriorated, and ethylene will be difficult to polymerize randomly, resulting in a film with poor transparency. A method of using a copolymer of α-olefin and propylene other than ethylene as a heat-sealing layer has also been proposed.
No. 128781 describes propylene and 4 to 10 molecules in the molecule.
a copolymer with an α-olefin having 1-butene carbon atoms, the propylene content being 80 to 95% by weight (84.2 to 96.2 mol% when the α-olefin is 1-butene) based on the copolymer. A method of using the coalescence as a heat seal layer is disclosed.
However, when the present inventors conducted additional tests, the propylene-1-butene polymer polymerized using the titanium trichloride catalyst disclosed in the above-mentioned publication had an appropriate heat-sealing temperature of 130°C or higher, and as mentioned above, Compared to the ethylene-propylene random copolymer, it was not much improved in terms of low-temperature heat-sealing properties and changes in heat-sealing properties over time, and could not be said to be satisfactory. Conventionally known propylene-1-
Even with butene copolymers, increasing the ratio of 1-butene, which is a copolymerization component, lowers the melting point and improves low-temperature heat sealing properties, but there is a problem that the resin becomes sticky. . As a result of intensive 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 low adhesion and blocking properties. The present invention was achieved based on the discovery that a polypropylene composite film can be obtained with no polypropylene. The main object of the present invention is to use polypropylene which has superior low-temperature heat sealing properties than conventionally proposed propylene-1-butene copolymers and ethylene-propylene copolymers, and which has good blocking resistance. The purpose is to obtain a composite film.
Another object of the present invention is to obtain a polypropylene composite film that has good heat-sealing strength and exhibits little change over time. Still another object of the present invention is to obtain a polypropylene composite film that has excellent transparency and good scratch resistance. That is, the present invention provides a base material layer consisting of an unstretched layer of isotactic polypropylene, on at least one side of which has a melt index of 0.1 to 100, a propylene content of 60 to 80 mol%, and a crystal based on thermal analysis using a differential scanning calorimeter. Heat of fusion is 20 or less
70Joule/g, boiling methyl acetate soluble content is 2.0% by weight
This is a polypropylene composite film characterized in that a propylene-1-butene random copolymer layer having the following properties and having a boiling n-heptane insoluble content of 5.0% by weight or less is laminated thereon. The polypropylene used in the present invention has a density of 0.89
or 0.92g/cm ³ , melt index (230℃)
A crystalline polypropylene used for films with an isotactic index (insoluble content in boiling n-heptane) of 75 to 98%, usually obtained by polymerizing almost only propylene monomers. . Heat stabilizers, ultraviolet absorbers, antiblocking agents, slip agents, antistatic agents, etc. may 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 composite film of the present invention has the following characteristics. (i) Melt index (ASTM-D-1238-
65T, 230℃) is 0.1 to 100, preferably 1
(ii) a propylene content of 60 to 80 mol%, especially 65;
(iii) Heat of crystal fusion is 20 to 70 Joule/g, (iv) Boiling methyl acetate soluble content is 2.0% by weight or less, preferably 1.0% by weight or less, (v) Boiling n-heptane insoluble content is 5.0% by weight or less. weight% or less,
Preferably 3.0% by 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, moldability will be poor, making it difficult to obtain a thin layer of 10 μm or less, which is desirable as a heat-sealing layer.On the other hand, if it exceeds 100, heat-sealing strength will be poor. Melting point Tm (℃) of propylene-1-butene random copolymer used in the present invention
is the melting point Tm (℃) of a copolymer with a propylene content of y mol%, which is usually in the range of 75 to 140℃
is usually in the range 1.4y-16≦Tm≦1.4y+24, and often in the range 1.4y-11≦Tm≦1.4y+19. Therefore, if the propylene content exceeds 87 mol%, the melting point of the resin will be 140°C or higher and the appropriate heat sealing temperature will be 130°C or higher, which is almost the same as the propylene-1-butene copolymer proposed previously. Not suitable for the purpose of the invention. On the other hand, a polymer having a propylene content of less than 50 mol % has excellent low-temperature heat-sealing properties, but is not preferred because it has poor bonding properties to the base polypropylene and poor scratch resistance. Furthermore, the film suffers from blocking during storage, making it unusable. The heat of fusion (iii) is a value that correlates with the degree of crystallinity of the polymer, but propylene-1 that can be used in the present invention
-Butene random copolymers are less crystalline at the same propylene content than those made with titanium trichloride-based catalysts, 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-sealing 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 less than 10 Joule/g,
It cannot be used because it lacks scratch resistance, tends to block, and has a sticky feel.
On the other hand, if the heat of fusion exceeds 80 Joule/g, the degree of crystallinity increases and the low-temperature heat-sealability becomes comparable to that of propylene-1-butene copolymers that have been proposed in the past, which is not suitable for the purpose of the present invention. In particular, a polymer having a heat of fusion in the range of 20 to 70 Joule/g is preferred from the viewpoint of a good balance between low temperature heat sealing properties and sex blocking properties. The heat of fusion of the polymer in the present invention is measured using a differential scanning calorimeter (DSO) using a specific heat curve of the copolymer in a completely molten state (preferably 160°C or higher).
This value is calculated using the straight line obtained by directly extrapolating the specific heat curve shown below 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 200℃ for 5 minutes,
Cool down to -40℃ at a rate of ℃/min, and cool down to -40℃ for 5 minutes.
Leave for a minute. After that, at a heating rate of 20℃/min -
Measurements are taken from 40℃ to 200℃. Boiling n-heptane insoluble content is one measure of the randomness of a copolymer. Copolymers proposed for titanium trichloride catalysts have a large amount of boiling n-heptane insoluble matter and generally have poor transparency.
The amount used in the present invention is small, and this contributes to the good transparency. The boiling n-heptane insoluble content of the copolymer used in the present invention is usually 5.0% by weight or less,
It is preferably 3.0% by weight or less, more preferably 2.0% by weight or less. The amount insoluble in boiling n-heptane is determined by the following method. That is, approximately 1mm x 1
A sample strip of approximately mm x 1 mm and glass beads are placed in a cylindrical glass filter (G3), and extracted using a Soxhlet extractor for 14 hours. In this case, the reflux frequency is approximately once/5 minutes. The weight percent of insoluble matter is determined by weighing the dissolved or insoluble matter. The boiling methyl acetate soluble content is a measure of the breadth and narrowness of the composition distribution and molecular weight distribution, and the previously proposed copolymers have a large boiling methyl acetate soluble content, which is the reason for the high surface tackiness (stickiness). It's summery. In the present invention, it is usually 2.0% by weight or less, preferably 1.0% by weight.
It is not more than 0.5% by weight, more preferably not more than 0.5% by weight. Quantification of boiling methyl acetate soluble content is 1 mm x 1 mm.
A strip sample of approximately 1 mm in size is placed in a cylindrical glass filter and extracted using a Soxhlet extractor for 7 hours with a reflux frequency of approximately 1 time/5 minutes. The soluble content is determined by drying the extracted residue in a vacuum dryer (vacuum level 10 mmHg or less) until it reaches a constant weight. As long as it has the above properties, the copolymer used in the present invention can contain trace amounts of other α-olefins,
For example, ethylene may be copolymerized. Propylene content with the above properties
50 to 87 mol % propylene-1-butene random copolymer is, for example, (a) a complex containing at least magnesium, titanium and halogen; (b)
It can be obtained by random copolymerization of propylene and 1-butene using a catalyst formed from an organometallic compound of a metal from Group 1 to Group 3 of the periodic table and (c) an electron donor. The above electron donor
Part or all of (c) may be immobilized on part or all of the complex (a), or may be preliminarily contacted with the organometallic compound (b) prior to use. Particularly preferably, part of the electron donor (c) is a complex (a).
The remainder is added to the polymerization system as it is or is used after preliminary contact with the organometallic compound (b). Using such a catalyst system, a copolymer with less methyl acetate soluble content is obtained. In this case, the electron donor fixed on the complex (a) and the polymerization system can be added directly to the polymerization system, or
The electron donor used in preliminary contact with (b) may be the same or different. The propylene-1-butene random copolymer used as the heat-sealing layer of the polypropylene composite film of the present invention described above contains heat-resistant stabilizers, ultraviolet absorbers, anti-blocking agents, and slip agents in order to improve the performance of the film. , an antistatic agent, etc. can be added as necessary. Further, in order to improve the overlap packaging property and the adhesion to metals, etc., part or all of the propylene-1-butene random copolymer may be modified with an unsaturated carboxylic acid or its anhydride. The polypropylene composite film of the present invention is a composite film in which a specific propylene-1-butene random copolymer layer described above is laminated on one or both sides of a crystalline, unstretched polypropylene film serving as a base material. One side of the polypropylene film serving as the base material may be subjected to corona treatment by a conventional method. The following method is possible for producing the polypropylene composite film of the present invention. (1) A method of coextruding a propylene-1-butene random copolymer and crystalline polypropylene. (2) A method of extruding and laminating a propylene-1-butene random copolymer in a molten state on a crystalline polypropylene film. (3) A method of laminating a crystalline polypropylene film and a propylene-1-butene random copolymer film with an adhesive. The unstretched crystalline polypropylene layer, which is the base layer of the polypropylene composite film of the present invention, has a thickness in the range of 5 to 200μ, preferably 10 to 60μ, and the propylene-1-butene random copolymer layer has a thickness in the range of 5 to 200μ, preferably 10 to 60μ. 2 to 100μ, preferably 3 to 100μ
It is in the range of 30μ. The polypropylene composite film according to the present invention is
It has better heat-sealability than conventional products, so it can be heat-sealed at lower temperatures. Therefore, heat sealability is possible over a wide temperature range, and problems caused by poor sealing are improved. The film's transparency, scratch resistance, blocking resistance, and heat seal strength are also maintained at high levels. The polypropylene composite film of the present invention is suitable for uses such as food packaging, clothing packaging, and textile packaging. Next, the polypropylene 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 composite film were measured by the following methods. (1) Haze Measured according to the method of ASTM-D-1003. (2) Heat seal adhesive strength Propylene of polypropylene composite film
The surfaces on which the 1-butene random copolymer is laminated are stacked together, and heated at 90℃, 100℃, 110℃,
After heat-sealing with a seal bar width of 5 mm at temperatures of 120°C, 130°C and 140°C and a pressure of 2 kg/cm ² for 1 second, the pieces were allowed to cool. Cut a 15 mm wide test piece from this sample and set it at a crosshead speed of 200.
The strength when the heat-sealed part is peeled off is shown in mm/min. (3) Change in heat seal adhesive strength over time The molded polypropylene composite film was heated at 50°C.
After being left for one week, heat sealing was performed using method (2), and the peel strength was measured. (4) Blocking resistance Measured by the method of ASTM-D-1893. (5) Scratch resistance Layer bleached kraft paper without sizing the surface so that it corresponds to the heat seal, rub it together at a speed of 500 mm/min with a 500 g iron block as a load, and then visually judge the extent of scratches. Example 1 [Production of copolymer] 200 g of anhydrous magnesium chloride, 46 ml of ethyl benzoate, and 30 ml of methylpolysiloxane were placed as the catalyst component (a) in 20 stainless steel polymerization vessels equipped with stirring blades under nitrogen gas. Ball-milled in an atmosphere, then suspended in titanium tetrachloride, the filtered material was added so that the titanium concentration was 0.01 mmol/triethylaluminum (b) was added to the polymerization vessel so that the concentration was 1.0 mmol/ In addition, p-methyl toluate was supplied as the electron donor (c) so that the concentration in the polymerization vessel was 0.33 mmol/n-heptane was used as the polymerization solvent, and propylene and 1-
A copolymerization reaction was carried out at 70° C. by supplying a mixed gas of butene (55 mol % propylene, 45 mol % 1-butene) at a rate of 4 K/hour. The propylene content of the thus obtained propylene-1-butene random copolymer measured by nuclear magnetic resonance spectroscopy was 66.5 mol%, and the melting point was 106.
°C, heat of fusion 44Joule/g, melt index
2.09, the content insoluble in boiling n-heptane was 0.5%, and the content soluble in boiling methyl acetate was 0.4%. [Forming of composite film] A phenolic stabilizer was blended into the propylene-1-butene random copolymer obtained by the above method, and then granulated at 210°C using an extruder. Next, the obtained pellets were melted in one extruder and fed to a composite film molding die at a resin temperature of 230°C. On the other hand, in another extruder, a propylene homopolymer having a melt index of 6.5 and having a boiling n-heptane extraction residue of 96% was melted and fed to the die at a resin temperature of 260°C. By the above method, a composite film having a base layer thickness of approximately 25 μm and a heat seal layer thickness of approximately 5 μm was obtained. Example 2 In the production of the copolymer of Example 1, a propylene content of 84.5 mol% and a melting point of 136 were obtained by changing the mixing ratio of the mixed gas of propylene and 1-butene.
°C, heat of fusion 75 Joule/g, melt index
Example 1 was carried out in the same manner as in Example 1, except that a propylene-1-butene random copolymer with a boiling n-heptane 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. Comparative Example 7 In the production of the copolymer of Example 1, a propylene content of 77.0 mol% and a melting point of 120 were obtained by changing the mixing ratio of the mixed gas of propylene and 1-butene.
°C, heat of fusion 56 Joule/g, melt index
The same procedure as in Example 1 was carried out except that a propylene-1-butene random copolymer with a boiling n-heptane insoluble content of 0.6% and a boiling methyl acetate soluble content of 0.3% was used. The results are shown in Table 1. Example 3 Propylene content 72.5 mol%, melting point 115°C, heat of fusion 52 Joule/g, melt index 0.91 obtained by changing the mixed gas ratio of propylene and 1-butene in the production of the copolymer of Example 1. The same procedure as in Example 1 was carried out except that a propylene-1-butene random copolymer having a boiling n-heptane insoluble content of 0.5% and a boiling methyl acetate soluble content of 0.35% was used. The results are shown in Table 1. Example 4 In the production of the copolymer of Example 1, the propylene content was 55 mol%, the melting point was 85°C, the heat of fusion was 28 Joule/g, and the melt index was obtained by changing the mixing ratio of the mixed gas of propylene and 1-butene. The same procedure as in Example 1 was carried out except that a propylene-1-butene random copolymer having a content of 2.9% Tx, a boiling n-heptane insoluble content of 0.3%, and a boiling methyl acetate soluble content of 0.34% was used. 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°C, the heat of fusion was 97 Joule/g, and the melt index was obtained by changing the mixing ratio of the mixed gas of propylene and 1-butene. Tux 1.23,
The same procedure as in Example 1 was conducted except that a propylene-1-butene random copolymer having a boiling n-heptane insoluble content of 13.6% and a boiling methyl acetate soluble content of 0.15% 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°C, the heat of fusion was 1.7 Joule/g, and the melt was obtained by changing the mixing ratio of the mixed gas of propylene and 1-butene. The same procedure as in Example 1 was carried out except that a propylene-1-butene random copolymer having an index of 3.2, a boiling n-heptane insoluble content of 0.3%, and a boiling methyl acetate soluble content of 0.65% was used. The results are shown in Table 1.

[Table] Example 5 A copolymer was produced in the same manner as in Example 1 except that toluene was used instead of n-heptane as the polymerization solvent and the mixing ratio of propylene and 1-butene in the feed gas was changed. Propylene content 66.5 mol%, melting point 104℃, heat of fusion 38 Joule/
Example 1 was repeated except that a propylene-1-butene random copolymer having a melt index of 0.90, a boiling n-heptane insoluble content of 0.3%, and a boiling methyl acetate soluble content of 0.18% was used. The results are shown in Table 2. Example 6 In the production of the copolymer of Example 1, dimethyl ether was used at a rate of 1.0 mmol/g instead of methyl p-tolurate as the electron donor (c), which is a component of the polymerization catalyst, and was supplied. Propylene content 66.5 mol%, melting point 106, obtained in the same manner except for changing the gas mixture ratio of propylene and 1-butene.
°C, heat of fusion 30Joule/g, melt index
The same procedure as in Example 1 was carried out except that a propylene-1-butene random copolymer having a boiling n-heptane insoluble content of 0.3% and a boiling methyl acetate soluble content of 0.6% was used. The results are shown in Table 2. Comparative Example 3 In the production of the copolymer of Example 1, titanium trichloride was used as a polymerization catalyst instead of components (a), (b), and (c) so that the titanium concentration in the polymerization vessel was 5 mmol/. Also, diethyl aluminum monochloride
Propylene content 84.2 mol%, melting point (95°C and 142°C), heat of fusion obtained in the same manner except that the mixing ratio of propylene and 1-butene in the supplied gas was changed. 72Joule／
Example 1 was repeated except that a propylene-1-butene random copolymer having a melt index of 12, a boiling n-heptane insoluble content of 28%, and a boiling methyl acetate soluble content of 2.4% was used. The results are shown in Table 2. Comparative Example 4 A copolymer was obtained in the same manner as in Example 1 except that vanadium oxytrichloride was supplied as a polymerization catalyst at a rate of 4 mmol/diethyl aluminum monochloride at a rate of 3.5 mmol/. Propylene content: 66.5 mol%, melting point: not observed, heat of fusion: 0 Joule/g,
The same procedure as in Example 1 was carried out except that a propylene-1-butene random copolymer having a melt index of 2.5, a boiling n-heptane insoluble content of 0%, and a boiling methyl acetate soluble content of 0.5% was used. The results are shown in Table 2. Comparative Example 5 Propylene-ethylene block copolymer produced using the catalyst of Example 1 (ethylene content 20
Example 1 was carried out in the same manner as in Example 1 except that 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 Example 1 (propylene content:
94 mol%, melting point 152℃, heat of fusion 104Joule/g,
The same procedure as in Example 1 was carried out except that the melt index was 0.55, the content insoluble in boiling n-heptane was 68%, and the content soluble in boiling methyl acetate was 0.6%. The results are shown in Table 2.

【table】

Claims (1)

[Scope of Claims] 1. On at least one side of a base material layer consisting of an unstretched layer of isotactic polypropylene, a melt index of 0.1 to 100, a propylene content of 60 to 80 mol%, and a thermal analysis using a differential scanning calorimeter are applied. Laminated layers of propylene-1-butene random copolymer having a heat of crystal fusion of 20 to 70 Joule/g based on A polypropylene composite film characterized by: 2. 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. 3. The film according to claim 1, wherein the propylene-1-butene random copolymer has a boiling n-heptane insoluble content of 3.0% by weight or less.