JPH0245975B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a composite polypropylene resin stretched film. More specifically, the present invention relates to a method for producing a composite polypropylene resin stretched film with good dimensional stability and good appearance and good moldability. An opaque film can be obtained by uniaxially or biaxially stretching a thermoplastic resin film blended with inorganic fine powder (hereinafter sometimes referred to as filler) at an appropriate temperature. This film is similar to pulp paper in its opacity, whiteness, texture and feel, and can be used as a single-layer structure consisting only of this film or as a multi-layer structure on the surface layer of conventional pulp paper. It is known that paper can be used for various purposes.
No. 46-40794, Japanese Patent Application Publication No. 57-53349). Stretched films made of filler-containing thermoplastic resins are opaque and white because peeling occurs at the interface between the resin and filler particles during film stretching, and as the stretching progresses, fine gaps form between the resin and filler particles. At the end of stretching, fine voids containing filler particles are formed inside the film, and the closed shape of the voids is not maintained near the film surface, resulting in the formation of fine cracks on the surface. This is because light is scattered on the film surface and inside the film. These surface cracks and internal voids give the film properties similar to pulp paper. However, when performing secondary processing such as printing, folding, bookbinding, and bag making on such opaque film,
Voids near the surface break their closed structure and become surface cracks, resulting in a polypropylene resin with a melt flow rate (MFR) of 0.5 to 5 in order to have sufficient mechanical strength and extensibility as a free or semi-free layer on the surface. When such laminated structures were manufactured using filler with a filler content of 20 to 68% in order to obtain sufficient opacity, several problems were found. That is, the laminated structure is obtained by making a longitudinally stretched sheet of polypropylene resin for the base material layer in advance, melting and laminating the polypropylene resin for the paper-like layer on at least one side of the sheet, and stretching the resulting laminated sheet in the transverse direction. However, the following drawbacks were observed due to the base layer being a polypropylene resin with low MFR and high filler content. (1) Burnt and degraded resin adheres to and accumulates in the slit of the die that extrudes the base layer sheet, causing streaks on the surface of the extruded sheet. As a result, stretching is not performed uniformly, and when light is transmitted through the resulting composite stretched film, streak-like opacity unevenness is visible. (2) When the melt-extruded sheet for the base material layer is cooled, shrinkage occurs with the filler particles as the core, resulting in numerous depressions on the sheet surface. As a result, many unstretched portions (so-called "dimples") the size of grains of rice are visible in the resulting composite stretched film. (3) Polypropylene resin sheets with low MFR and high filler content are difficult to stretch, and together with the formation of the above-mentioned depressions, the stretching tends to be uneven. In order to improve the above drawbacks (1), (2) and (3), we first melt-laminated a polyolefin resin sheet for a paper-like layer on at least one side of a uniaxially stretched polyolefin resin sheet for a base layer. The resulting laminated sheet is stretched in a direction perpendicular to the stretching direction, and the base layer polyolefin resin sheet is coated with the following composition (A) on one side of the intermediate layer made of the following composition (B). ) is melt-coextruded from one die so that a layer consisting of the following composition (C) is provided on the other side, and the above-mentioned polyolefin resin sheet for the paper-like layer proposed a method for producing synthetic paper characterized in that it consists of the following composition (D) (Japanese Patent Application Laid-Open No. 181829-1989).
issue). Composition (A) A thermoplastic resin composition containing 0 to 18% by weight of inorganic fine powder. Composition (B) A polyolefin resin composition containing 20 to 68% by weight of inorganic fine powder. However, the melt index of this polyolefin resin is 0.5 to 3 g/10 minutes. Composition (C) A thermoplastic resin composition containing 0 to 18% by weight of inorganic fine powder. Composition (D) A polyolefin resin composition containing 5 to 50% by weight of inorganic fine powder. However, the melt index of this polyolefin resin is 3 to 12 and is larger than that of the polyolefin resin of composition (B). In this manufacturing method, a polyolefin resin sheet with low MI and high filler content for the base layer is coated with a resin layer with low to no filler content, and this composite sheet is melt extruded from a single coextrusion die. By creating this, we have succeeded in solving the problems mentioned above. This manufacturing method has a composite film take-up speed of 40 m/min.
There was no problem if it was less than 1 minute, but this time we considered increasing the composite film take-up speed (80 m/min) to increase the molding cycle.
The following new problem has occurred. That is, as shown in FIG. 1, one surface of the base layer sheet 2 extruded from the coextrusion die 1 is first cooled by the cooling roll 3, and the other surface is cooled by the cooling roll 4. When the speed at which the composite film is taken up is increased, it is necessary to cool the sheet 2 quickly and lower the temperature of the sheet 2 to a temperature suitable for longitudinal stretching. Therefore, conventionally, in the case of polypropylene resin sheets, the temperature of the cooling rolls 3 and 4 was 50 to 70°C.
℃ would have been sufficient, but unless the temperature is lowered to 20 to 40℃, sheet cooling will not be sufficient. However, by adjusting the temperature of this cooling roll to 20-40℃,
When the composite film was taken at a speed of 80 m/min, the sheet 2 peeled off from the surface of the cooling roll 3.
It was found that this caused uneven stretching. The reason for this is that the raw sheet 2 for the base material layer has not yet been biaxially stretched and has a thick wall thickness of 2 to 4 mm, and if the sheet is cooled too quickly, the volume shrinks due to the solidification of the resin on the surface of the roll 3. occurs, and this causes sheet 2 to roll 3.
It seems like it will peel off from the surface. The present inventors have developed polypropylene compositions (A) and (C) for the front and back layers of the base material sheet to prevent this peeling.
Based on the idea that the peeling problem would be solved if the crystallization time was longer, we changed the blending amount of the inorganic fine powder and added other resins, stabilizers, lubricants,
When we investigated the crystallization time by adding dispersants, etc., we found that the type and amount of inorganic fine powder and other resins did not have a large effect on the crystallization time, but the addition of auxiliary agents such as lubricants and dispersants It has been found that the crystallization time of polypropylene is significantly affected, and
If a polypropylene resin composition exhibiting an isothermal crystallization rate at 130°C of 300 seconds or more, preferably 450 seconds or more, is used as the resin for the coating layers (A) and (C) of the base layer (B), the cooling roll 3 They have discovered that the sheet 2 can be prevented from peeling off, and have arrived at the present invention. That is, the present invention involves melting and laminating a polypropylene resin sheet for a paper-like layer on at least one side of a uniaxially stretched polypropylene resin sheet for a base material layer, and stretching the resulting laminated sheet in a direction perpendicular to the stretching direction. The above-mentioned polypropylene resin sheet for the base layer has a layer made of the following composition (A) on one side of an intermediate layer made of the following composition (B), and a layer made of the following composition (C) on the other side. It is a composite structure sheet obtained by melt coextrusion from a single die so as to form a layer, and is characterized in that the polypropylene resin sheet for the paper-like layer is composed of the following composition (D). A method for producing a composite polypropylene resin stretched film is provided. (A) and (C): 5 mg of sample was heated at 8℃/distance using a differential thermal analyzer.
After increasing the temperature to 250°C at a rate of 8°C/min and holding it at the same temperature for 3 minutes, the sample was cooled to 130°C at a rate of 8°C/min and the sample was held at that temperature.
When the time from the start of holding the temperature of °C until reaching the maximum exothermic peak is defined as the isothermal crystallization time at 130 °C, if the isothermal crystallization time at 130 °C is 300 seconds or more and the inorganic fine powder is % or less of polypropylene compositions. (B) A polypropylene resin composition containing 2 to 50% by weight of inorganic fine powder. However, this composition (B) has a higher content of inorganic fine powder than the above (A) and (C). (D) 8 to 65% by weight of inorganic fine powder or 30 to 60% of thermoplastic resin other than polypropylene
A polypropylene resin composition containing % by weight. In the present invention, the polypropylene composition of the base layer (B) contains 2 to 50% by weight of inorganic fine powder in order to create fine voids inside the film during stretching. Examples of the inorganic fine powder include calcium carbonate, clay, talc, diatomaceous earth, titanium oxide, barium sulfate, etc. with a particle size of 0.05 to 15 microns.
The polypropylene resin for this composition (B) is MFR
should be between 0.5 and 3, preferably between 1 and 3. This is because if the MFR is less than 0.5, even if it has good creep resistance, the amount of film extruded will be small and productivity will not improve.On the other hand, if the MFR of the polypropylene for the base material layer is greater than 3, the base material layer will be thick. This is because in the case of meat, uniform stretching is difficult and uneven stretching tends to occur. Note that it is desirable that the MFR of the polypropylene resin for composition (B) is one or more lower than that of the polypropylene resin for composition (D) from the viewpoint of lateral stretch formability. The layer consisting of compositions (A) and (C) covers both sides of the intermediate layer consisting of composition (B) with low MFR and filler content to prevent the generation of burnt resin during coextrusion from one die. The resins for compositions (A) and (C) should first have an MFR equal to or greater than that of the polypropylene resin for composition (B). The preferred MFR is 1 to
It is about 5. Compositions (A) and (C) should then be free of filler or contain up to 5% by weight filler, preferably from 0.3 to 1% by weight. In order to prolong the crystallization time of polypropylene, these layers (A) and (C) are made of fatty acids with 12 to 21 carbon atoms such as capric acid, oleic acid, and linolenic acid; stearic acid metal salts (Al, Zn, etc.); stabilizers 2,6-di-tert-butyl para-cresol, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate, tri(monononylphenyl) phosphite , tri(dinonylphenyl) phosphite, distearyl pentaerythritol diphosphite, etc., and adjust the isothermal crystallization time at 130° C. to be 300 seconds or more, preferably 450 seconds or more, more preferably 500 seconds or more. Specific examples of preferred formulations are as follows. (a) Polypropylene 95-99.4% by weight (b) Inorganic fine powder 0.3-3% by weight (c) Oleic acid 0.2-1% by weight (d) Stabilizer 0-3% by weight. In order to produce a multilayer structure sheet for the base material layer by melt coextruding these compositions (A), (B) and (C) from one die, any suitable This can be done by means. Specifically, for example, compositions (A), (B), and (C) are kneaded using separate extruders (3 units) (composition (A) and
(C) is the same, it goes without saying that two extruders are sufficient), the melt is guided through a conduit to one coextrusion die, and at that time, the composition (B) is mixed with the intermediate layer. This intermediate layer and the layer consisting of compositions (A) and (C) were laminated in a coextrusion die, extruded into a sheet form from a coextrusion die slit, and cooled at a temperature of 20 to 40°C. Cool to a temperature below 60°C using rolls 3 and 4. Also, the blackbox or feedblock method (JP-A No. 49-35467, No. 50-354)
159575, Japanese Patent Publication No. 57-59048), the compositions (A), (B) and (C) may be introduced into a conduit, laminated in the conduit, and then coextruded through a die and cooled.
This is heated to an appropriate temperature for stretching, that is, a temperature lower than the melting point of the polyolefin resin constituting composition (B) and at which stretching is possible. Stretch up to 10 times, preferably 4 to 8 times. The thickness structure of the base material layer is a layer consisting of compositions (A) to (C).
The ratio of (A):(B):(C) is (0.005~0.5):1:(0.005~
0.5) is preferable. As for the polypropylene constituting the composition (D) for the paper-like layer of synthetic paper, except for the conditions regarding the MFR value,
The same or different types of polypropylenes described above for compositions (A) and (C) can be used. The polypropylene for composition (D) has an MFR of 3 to
12, preferably 4 to 8. As mentioned above, it is desirable that this MFR value differs by at least 1 from that of the polypropylene for composition (B). Since the composition (D) constitutes the surface layer of the product composite stretched film, it contains an inorganic filler or a different resin in order to achieve writability or printability. The inorganic filler content is in the proportion of 8-65% by weight;
Resins other than polypropylene, such as thermoplastic resins such as polyethylene, polyethylene terephthalate, and polyamide, are used in an amount of 30 to 60% by weight.
When an inorganic fine powder and a thermoplastic resin other than polypropylene are used together, the thermoplastic resin may be less than 30% by weight. As the inorganic fine powder used as the filler, the same or different types of those described above for composition (B) can be used. In order to produce synthetic paper using the longitudinally stretched base layer film and this composition (D), the composition is applied to at least one side, preferably both sides, of the uniaxially stretched multilayer sheet for the base layer. Sheets made of (D) are laminated by melt extrusion and cooled to a temperature of 80°C or less. This is reheated to an appropriate temperature for stretching, that is, a temperature lower than the melting point of the polypropylene resin constituting composition (B) and at which stretching is possible, e.g. A composite stretched film (synthetic paper) is obtained by stretching the film in the transverse direction by 2.5 to 12 times, preferably 4 to 10 times, followed by heat setting and cooling, and cutting off the edges. The synthetic paper can be taken at a speed of 40 to 150 m/min. In addition, if the surface layer made of composition (D) is so thin that it is predicted that it will be difficult to extrude it and stretch the resulting laminated sheet, this layer and the base layer should not be extruded separately. It is preferable to coextrude a polypropylene resin containing no filler or with a low filler content (10% by weight or less) between the material layer and melt-laminate it onto the base material layer. The composite stretched film produced according to the present invention has a large number of fine pores therein due to the fact that the layer from composition (B) in the base layer contains an inorganic filler. ing. The filler-containing surface layer (D) has surface cracks centered around the filler particles, so it has a paper-like feel, and
Good absorption of offset printing ink. It goes without saying that the surface layer also has micropores inside. Here, the number of fine pores is determined by the following formula: the pore content is 1 to 60% in the surface layer, preferably 3 to 35%,
The value is 10 to 80%, preferably 25 to 60% in the intermediate layer of the base material layer (composition (B)). Void content (%) = ρ ₀ - ρ / ρ ₀ × 100 However, ρ ₀ = Apparent density of the film before stretching ρ = Apparent density of the film after stretching The thickness of each layer of this composite stretched film is Can be set arbitrarily. The preferred thickness and thickness ratio are that the surface layer (D) is 3 microns or more, the thickness ratio in the composite film is 1/4 or less for each surface layer, and the composition
The thickness of the layers consisting of (A) and (C) is 0.2 to 30
The thickness of the intermediate layer (composed of composition (B)) is 15 to 600 microns, and the thickness ratio in the composite film is 1/3 or more, preferably 1/2 or more. It is. Measurement of isothermal crystallization time: The isothermal crystallization time of the polypropylene resin composition shown in Table 1 was measured at 125°C, 130°C, 135°C, and 140°C. The results are shown in the same table. The abbreviations for stabilizers, dispersants, and lubricants in the table are as follows. [Dispersant] Lunatsk OA: Oleic acid [Lubricant] St-Al: Dialuminum stearate [Stabilizer] A mixture containing 0.1wt% each of the following (i), (ii), and (iii) (i) Ciba・“Irganox 1076” manufactured by Geigy Octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate (ii) “Mark 329” manufactured by Adeka Argus Tri(monononylphenyl) phosphite and tri( mixture with dinonyl phenyl) phosphite (iii) “Yoshinox BHT” manufactured by Yoshitomi Pharmaceutical Co., Ltd. 2,6-di-tert-butyl para-cresol [ultraviolet absorber] ●Sanol 770 [product name manufactured by Sankyo Co., Ltd.]: Bis(2,2, 6,6-tetramethyl-4
-piperidyl) sebacate ●Sanol 622 [trade name manufactured by Sankyo Co., Ltd.]: Dimethyl succinate polymer (4-hydroxy-2,2,6,6-tetramethyl-
1-piperidine ethanol [polypropylene] MA-6: Propylene homopolymer “Mitsubishi Noblen MA-6” manufactured by Mitsubishi Yuka Co., Ltd. [trade name,
MFR1.2g/10min, MP163-164℃] MA-3: Propylene homopolymer “Mitsubishi Noblen MA-3” manufactured by Mitsubishi Yuka Co., Ltd. [Product name,
MFR6g/10 minutes, MP162-163℃〕Modic: Maleic anhydride grafted polypropylene “Modic” manufactured by Mitsubishi Yuka Co., Ltd. [Product name, MFR8g/10 min] [High-density polyethylene] EY-40: Mitsubishi Yuka Co., Ltd. ) high-density polyethylene (melting point 134°C) Peeling of the raw sheet from the cooling roll: Compositions (A) and (C): Polypropylene compositions shown in Table 1 Composition (B) Polypropylene MA-6 73.7 Weight High density polyethylene EY-40 10 parts by weight Calcium carbonate 16 parts by weight Stabilizer 0.3 parts by weight Composition (D) Polypropylene MA-3 54.7 parts by weight Calcium carbonate 45 parts by weight Modic 0.3 parts by weight Stabilizer 0.7 parts by weight The above composition ( A), (B), and (C) are melt-kneaded using separate extruders, and then fed to one coextrusion die. After melting and laminating the objects (A) and (C) so that they are located on both sides, extrude the three-layer sheet with a wall thickness of 3 mm at a temperature of about 250℃, and roll it with a cooling roll of 600 mmφ (3 in the figure).
temperature 40℃) and a 400mmφ cooling roll (4 in the figure,
The sheet surface was cooled to approximately 40°C. At this time, the presence or absence of peeling of the original sheet from the cooling roll 3 was investigated. Next, this three-layer sheet is heated to about 140°C, and then stretched five times in the longitudinal direction using the difference in peripheral speed between the roll groups to obtain a three-layer uniaxially stretched sheet (for the base layer).
I got it. Separately, composition (D) was melt-kneaded using two separate extruders, laminated in a sheet form on both surfaces of the base material layer at a temperature of 250°C from a die, and once heated to a temperature about 30°C higher than room temperature. After cooling, about 150℃
The material was reheated to 100%, stretched approximately 9 times in the transverse direction using a tenter, and then passed through an oven at 160°C for heat setting, and the edges were slit to form a white opaque composite with a five-layer structure. Paper was obtained (the speed at which the synthetic paper was taken was 80 m/min). The thickness (in microns) of each layer of this synthetic paper was as follows. (D) / (A) / (B) / (C) / (D) = 25 / 10 / 58 / 10 / 25 In the above, the temperature of the cooling roll was changed to 30 to 55℃, and the temperature of the roll where sheet peeling occurred was changed. Temperature was measured. The temperatures are shown in Table 1. Judgment Criteria 〇: Peeling of the original sheet occurs or does not occur at a cooling roll temperature of 20 to 39°C. Δ: Peeling of the original sheet occurs at a cooling roll temperature of 40 to 49°C. x: Original sheet peeling occurs at a cooling roll temperature of 50 to 60°C.

[Table] Examples 1-2, Comparative Examples 1-2 Sample No. 1 (Comparative Example 1), Sample No. 4 (Comparative Example 2), Sample No. 9 (Example 1), Sample No. 12 (Example 2) )
was used as the composition of (A) and (C), and the 5 obtained in the above production
The suitability of each layer of synthetic paper as a synthetic paper was evaluated using the following method and criteria. The results are shown in Table 2. (1) Presence or absence of streaks When the synthetic paper was exposed to fluorescent light, it was determined whether or not streaks were visible. 〇 = Streaks are not visible △ = Streaks are slightly distinguishable, but there is no practical problem × = Streaks are clearly visible and there is a practical problem (2) Presence or absence of depressions The size of rice grains present in synthetic paper The number of depressions was expressed as follows. 〇 = None △ = 1 to 4 depressions per 10 m ² . × = 5 or more per ^10m2 (3) Paper texture Displayed according to the following. 〇 = Paper with sufficient whiteness and opacity as a printing paper, and a matte finish on the surface △ = Paper with a slight lack of opacity and a surface that is too smooth as a printing paper (4) Writability Mitsubishi Pencil Pencil HB The adhesion of pencil lead to vertical synthetic paper on which letters were written using was evaluated as follows. 〇=Writing was possible △=The adhesive of the pencil lead was slightly inferior. ×=The adhesive of the pencil lead was a practical problem. (5) Average wall thickness distribution This shows the wall thickness distribution in the width (horizontal) direction of synthetic paper.

[Table] Examples 3 to 5 Five-layer synthetic paper was obtained in the same manner as in Example 1, except that the composition of composition (D) was changed as shown in Table 3. The suitability of this synthetic paper is shown in the same table.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 shows a side view of an apparatus for producing an original sheet for a base material layer of synthetic paper. In the figure, 1 is a coextrusion die, 2 is a sheet material, 3 and 4 are cooling rolls, 5 is an extruder, and 6, 6, 6 are resin conduits.

Claims (1)

[Claims] 1. Melting and laminating a polypropylene resin sheet for a paper-like layer on at least one side of a uniaxially stretched polypropylene resin sheet for a base material layer, and stretching the resulting laminated sheet in a direction perpendicular to the stretching direction. The above-mentioned polypropylene resin sheet for the base layer has a layer made of the following composition (A) on one side of an intermediate layer made of the following composition (B), and a layer made of the following composition (C) on the other side.
It is a composite structure sheet obtained by co-melt extrusion from a single die so as to form layers, and the polypropylene resin sheet for the paper-like layer is made of the following composition (D).
A method for producing a composite polypropylene resin stretched film, comprising: (A) and (C): 5 mg of sample was heated at 8℃/distance using a differential thermal analyzer.
After increasing the temperature to 250°C at a rate of 8°C/min and holding it at the same temperature for 3 minutes, the sample was cooled to 130°C at a rate of 8°C/min and the sample was held at that temperature.
When the time from the start of holding the temperature of °C until reaching the maximum exothermic peak is defined as the isothermal crystallization time at 130 °C, if the isothermal crystallization time at 130 °C is 300 seconds or more and the inorganic fine powder is % or less of polypropylene compositions. (B) A polypropylene resin composition containing 2 to 50% by weight of inorganic fine powder. However, this composition (B) has a higher content of inorganic fine powder than the above (A) and (C). (D) 8 to 65% by weight of inorganic fine powder or 30 to 60% of thermoplastic resin other than polypropylene
A polypropylene resin composition containing % by weight. 2. The manufacturing method according to claim 1, wherein the compositions of (A) and (C) are the following compositions. (a) Polypropylene 95-99.4% by weight (b) Inorganic fine powder 0.3-3% by weight (c) Oleic acid 0.2-1% by weight (d) Heat stabilizer 0-3% by weight.