JP4198276B2 - Method for producing polypropylene resin sheet and polypropylene resin sheet - Google Patents

Description

【００３７】
【表２】

【００３８】
【発明の効果】
本発明によれば、横型加熱処理槽の場合に比較して、加熱処理温度を高く、しかも温度を均一化し易い。このため、透明性、剛性、耐熱寸法安定性がより高いレベルのポリプロピレン樹脂などの結晶性熱可塑性樹脂シートが得られる。また、間接加熱であり、シート表面の傷の発生、光沢などの表面特性もよい。さらに、高温、短時間処理が可能となり、生産性が向上するとともに、設備も簡略であり経済性にすぐれる。したがって、得られたポリプロピレン樹脂などのシートは、クリアボックス、クリアファイル、文具ケース、額縁カバーなどに好ましく用いられる。
【図面の簡単な説明】
【図１】 ポリプロピレン樹脂シートの製造方法に用いられる金属ベルトプロセスの主要部の概略図を示す。
【図２】 本発明のポリプロピレンシートの製造方法に用いられる加熱処理装置の一実施態様の概略図を示す。
【符号の説明】
１：溶融シート状樹脂
２：Ｔダイ
３：第１冷却ロール
４：第２冷却ロール
５：金属製エンドレスベルト
６：第３冷却ロール
７：第４ロール
８：弾性被覆層
９：回転軸
１０：第５ロール
１１：原反シート
２１：原反シートの製造装置
２２：予熱ロール
２３：加熱処理槽
２４：冷却ロール
２５：ガイドロール
２６：巻き取りロール
２７：加熱器
２８：加熱空気循環路
２９：ブロアー
３０：樹脂シート
３１：冷却風槽[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an efficient method for producing a crystalline thermoplastic resin sheet such as polypropylene resin having high transparency, high gloss, no scratches, good appearance, and excellent rigidity, and a polypropylene resin sheet. Available.
[0002]
[Prior art]
Polypropylene resin has excellent physical strength, heat resistance, chemical resistance, hinge characteristics, etc., but due to crystallinity, the sheet obtained by the usual manufacturing method is inferior in transparency and its application field is limited. Has been. In particular, clear boxes, clear files, and the like using hinge characteristics have not only high transparency, but also have a problem that slight surface scratches reduce the commercial value and are difficult to put into practical use.
[0003]
As a method for producing a transparent polypropylene resin sheet, there is a method of adding an additive such as a crystal nucleating agent or petroleum resin to a raw material polypropylene resin. As a forming method, a rapid cooling method is known. Examples of the rapid cooling method include an air knife method, a polishing roll method, a metal belt method, and a water cooling method. Among these rapid cooling methods, the air knife method and the polishing roll method have poor cooling efficiency, and in order to perform rapid cooling, it is necessary to slow down the film forming speed, and the practicality is low. Therefore, the metal belt method and the water cooling method have been put into practical use.
[0004]
Polypropylene resin sheets obtained by these quenching methods have excellent transparency due to low crystallinity, but have low rigidity and are used for thermoforming, but inherently high rigidity and high polypropylene resin. The heat resistance characteristics cannot be utilized. For this reason, for the uses such as the above-mentioned clear box and clear file, it is performed to heat the polypropylene resin sheet at a specific temperature to give rigidity suitable for the purpose of use. Conventionally, this heat treatment is generally a direct heat treatment in which the low crystallization polypropylene resin sheet is brought into contact with a plurality of heating rolls.
[0005]
In this direct heating method, the sheet was easily rubbed by a heating roll when the sheet was stretched during running of the sheet. The occurrence of this scratch is very conspicuous when the polypropylene resin sheet is highly transparent and highly glossy, and there has been a demand for a solution for the scratch in order to increase the commercial value. In order to solve this problem, the applicant of the present invention is characterized in that both ends of the low-crystallized polypropylene resin sheet are gripped, and the annealing is performed by indirect heating in a state where the central portion of the resin sheet is relaxed. A method for producing a polypropylene sheet was proposed (Japanese Patent Laid-Open No. 10-217342).
[0006]
In other words, this indirect heating method is an excellent manufacturing method in which a polypropylene resin sheet having not only contact with a roll and no generation of scratches but also excellent transparency and gloss can be obtained. However, in the heat treatment process, in order to move the sheet into the heating chamber, gripping means such as clips for gripping both ends of the sheet are necessary, and there are problems such as complicated equipment costs and operation operations. . In addition, since the sheet moves in the horizontal direction, the sheet is easily loosened by heating. Therefore, there is a limit to increasing the heat treatment temperature and increasing the processing speed. Furthermore, a superior manufacturing method is desired such that heating temperature unevenness tends to occur at the top and bottom of the sheet.
[0007]
[Problems to be solved by the invention]
The present invention is a highly transparent, quenching and low crystallization thermoplastic resin sheet made of a crystalline thermoplastic resin such as a polypropylene resin, and is heat-treated to produce a crystalline thermoplastic with excellent scratches, transparency, gloss and rigidity. An object of the present invention is to provide a production method with excellent productivity that can process a resin sheet at a high temperature and in a short time with simple equipment.
[0008]
[Means to solve the problem]
Under such circumstances, the present invention, as a result of intensive investigations on the relationship between the form of the heat treatment tank of a low crystallization thermoplastic resin sheet such as polypropylene resin and the properties of the obtained sheet, shows low crystallization thermoplasticity. It has been found that the above problems can be solved when the resin sheet is run in the vertical direction, and the present invention has been completed.
[0009]
That is, the present invention
(1) A method for producing a crystalline thermoplastic resin sheet, comprising subjecting a polypropylene resin sheet low crystallized by rapid cooling to an indirect heat treatment by running in a vertical heating tank in the vertical direction.
(2) The method for producing a polypropylene resin sheet according to the above (1), wherein the rapid cooling is performed by a metal belt method or a water cooling method.
(3) Density of low crystallinity polypropylene resin sheet is not more than 0.890 g / cm @ 3 above (1) or (2) method for producing a crystalline thermoplastic resin sheets described by quenching.
(4) the polypropylene resin is one that does not contain a nucleating agent (1) to a polypropylene resin sheet manufacturing method according to any one of (3).
(5) A polypropylene resin sheet obtained by indirect heat treatment of a polypropylene resin sheet low crystallized by rapid cooling by running in a vertical heating tank in the vertical direction,
(1) MD and TD tensile elastic moduli are both 1500 MPa or more, and (2) total haze is [330 t ² −150 t + 20 (t is sheet thickness: mm)] or less.
(6) The polypropylene resin sheet according to (5), wherein (1) MD and TD tensile elastic modulus is 2000 MPa or more, and (2) density is 0.905 g / cm ³ or more.
(7) The polypropylene resin sheet according to the above (5) or (6), wherein the expansion / contraction ratio at 90 ° C. in the MD and TD directions is within ± 1.0%.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The crystalline thermoplastic resin used for the production of the crystalline thermoplastic resin sheet of the present invention is a polypropylene resin such as a propylene homopolymer, a copolymer of propylene and a small amount of ethylene, butene and other olefins such as butene-1. And polyester resins such as polyethylene resin, polyethylene terephthalate and polybutylene terephthalate, and polyamide resins such as polyamide 6 and polyamide 66. Of these, polypropylene resin is preferably used. As the polypropylene resin, a homopolymer is preferably used from the viewpoint of rigidity, heat resistance and the like. Hereinafter, the crystalline thermoplastic resin will be described based on a polypropylene resin.
[0011]
The melt index (MI) of the polypropylene resin is [based on JIS K7210, 230 ° C., 2.16 kg load] 0.2 to 20 g / 10 minutes, preferably 0.3 to 10 g / 10 minutes.
The raw material polypropylene resin includes silica fine powder, talc, benzoic acid aluminum salt, pt-butyl benzoic acid aluminum salt, metal salts of aromatic carboxylic acids and aliphatic carboxylic acids such as sodium adipate, sodium-2 , 2′-methylene-bis- (4,6-di-t-butylphenyl) phosphate, sodium-bis- (4-tert-butylphenyl) phosphate, and the like, 1,3,2,4-di Nucleating agents such as sorbitols such as benzylidene sorbitol may be included.
[0012]
Further, a transparency improving agent such as petroleum resin may be included. However, the addition of the nucleating agent has a problem that the effect of improving the rigidity of the sheet after the heat treatment cannot be expected so much, and a polypropylene resin containing no nucleating agent is preferably used. In addition, the addition of petroleum resins and the like may deteriorate the appearance and surface characteristics due to a decrease in heat resistance, bleed of additives, etc. In the present invention, a polypropylene resin that does not substantially contain these additives is preferably used. It is done.
[0013]
Furthermore, in consideration of the use of the sheet, a known additive can be added as necessary. Examples of these other additives include antioxidants, heat stabilizers, lubricants, slip agents, antiblocking agents, antistatic agents, ultraviolet absorbers, light stabilizers, organic peroxides, pigments, and dyes.
First, an example of the manufacturing method of the low crystallization polypropylene resin sheet obtained by the rapid cooling film forming method used for the manufacturing method of the crystalline thermoplastic resin sheet of this invention is demonstrated based on drawing. FIG. 1 is a schematic view of a main part of a metal belt method used in a method for producing a low crystallized polypropylene resin sheet. In FIG. 1, 1 is a molten sheet-like polypropylene resin, 2 is a T die, 3 is a first cooling roll, 4 is a second cooling roll, 5 is a metal endless belt, 6 is a third cooling roll, and 7 is a fourth roll. , 8 is an elastic coating layer, 9 is a rotating shaft, 10 is a fifth roll, and 11 is a low crystallization polypropylene resin sheet.
[0014]
That is, the apparatus for producing the low crystallization polypropylene resin sheet 11 is a metal endless wound between a T die 2 of an extruder (not shown), a first cooling roll 3 and a second cooling roll 4. A third cooling roll 6 and a second cooling roll 4 provided in the vicinity of the first cooling roll 3 through the belt 5, the low crystallized polypropylene resin sheet 11, and the metal endless belt 5. 4 rolls 7.
[0015]
The surface of the first cooling roll 3 is covered with an elastic coating layer 8 such as NBR. This elastic coating layer 8 usually has a hardness (conforming to JIS K6301 A type) of 95 or less and a thickness of 3 mm or more. The metal endless belt 5 is made of stainless steel, titanium alloy, or the like, and has a mirror surface with a surface roughness of 0.5 S or less. Further, at least one of the first and second cooling rolls has a rotating shaft 9 connected to a rotation driving means (not shown).
[0016]
The third cooling roll 6 is made of metal and has a mirror surface with a surface roughness of 0.5S or less. The cooling roll 6 is in contact with the first cooling roll 3 via the molten sheet-shaped polypropylene resin 1 and the metal endless belt 5, and is pressed by the metal endless belt 5 toward the cooling roll 6. It is provided so as to embrace the polypropylene resin 1. That is, the metal endless belt 5 and the molten sheet-like polypropylene resin 1 in contact with the belt move so as to wrap around the outer peripheral surface of the third cooling roll 6.
[0017]
The fourth roll 7 guides the sheet so that the molten sheet-like polypropylene resin 1 is pressed against the second cooling roll 4 via the metal endless belt 5. The cooling rolls 3, 4, 6 are provided with temperature adjusting means (not shown) such as a water cooling type for adjusting the surface temperature. In addition, another cooling roll 10 can be provided before the first roll 3 of the metal endless belt 5 to precool the endless belt 5. The cooling roll 10 can also function as a tension adjusting roll for the endless belt. Here, the molten sheet-like polypropylene resin is sequentially cured with cooling, but the term “melted sheet” is used for convenience.
[0018]
In the production of the low-crystallized polypropylene resin sheet (hereinafter sometimes referred to as the original fabric sheet), the surface temperature of the metal endless belt 5 and the third cooling roll 6 is set to 50 ° C. or lower and the dew point or higher. The temperature of each cooling roll 3, 4, 6 is controlled. Polypropylene resin pellets are supplied to an extrusion molding machine, melted and kneaded, and extruded from the T-die 2. The extruded molten sheet-like polypropylene resin 1 has the first and third cooling rolls so as to contact the metal endless belt 5 in contact with the first cooling roll 3 and the third cooling roll 6 substantially simultaneously. 3 and 6, the molten sheet-like polypropylene resin 1 is pressed against the first and third cooling rolls 3 and 6 and rapidly cooled.
[0019]
During this cooling, the elastic coating layer 8 is elastically deformed by the pressing force between the first and third cooling rolls 3 and 6 so as to be compressed, and at a portion of the angle θ1 from the center of both rolls 3 and 6, the molten sheet The sheet-like polypropylene resin has a surface pressure contact. The surface pressure in this case is usually 0.1 to 20.0 MPa. Subsequently, the molten sheet-shaped polypropylene resin 1 is pressed against the third cooling roll 6 by the metal endless belt 5 having a mirror surface and cooled. The molten sheet-like polypropylene resin pressed to the cooling roll 6 side by the endless belt 5 is held in the cooling roll 6 at an angle θ2 from the center of the cooling roll 6, and the sheet-like polypropylene resin is a metal endless belt in this portion. 5 and the cooling roll 6 are pressed into a planar shape. The surface pressure at this time is usually 0.01 to 0.5 MPa.
[0020]
Next, the sheet-like polypropylene resin is moved and cooled to the second cooling roll 4 along with the movement of the endless belt in a state of being overlapped with the endless belt 5. In some cases, the sheet-like polypropylene resin cooled by the third cooling roll 6 can be taken as it is without being moved to the second cooling roll 4 (illustrated by a two-dot chain line in FIG. 1). .
[0021]
In this way, the melt-extruded molten sheet-like polypropylene resin is rapidly cooled, whereby crystallization is suppressed and a low-crystallized polypropylene resin sheet 11 is obtained, which is a raw fabric sheet used in the present invention. The original sheet is preferably formed under conditions such that the normal density is 0.890 g / cm ³ or less and the haze is [330 t ² −150 t + 20 (t is the sheet thickness: mm)] or less. Moreover, although the thickness of the obtained raw fabric sheet changes with uses, it is 100-1,000 micrometers normally, Preferably it is 200-500 micrometers.
[0022]
The low-crystallized polypropylene resin sheet thus obtained is used as a raw fabric sheet, and heat treatment is performed in order to increase the rigidity and heat resistance of the product sheet while ensuring transparency and gloss. In the heat treatment step, the present invention is characterized in that the raw sheet is caused to travel in the up and down direction in the heat treatment tank.
FIG. 2 shows a schematic view of one embodiment of a heat treatment apparatus used in the method for producing a crystalline thermoplastic resin sheet of the present invention. In FIG. 2, 21 is a raw sheet manufacturing apparatus, 11 is a raw sheet, 22 is a preheating roll, 23 is a heat treatment tank, 24 is a cooling roll, 25 is a guide roll, 26 is a take-up roll, and 27 is a heater. , 28 is a heated air circulation path, 29 is a blower, 30 is a crystalline thermoplastic resin sheet, and 31 is a cooling air tank.
[0023]
In FIG. 2, the raw fabric sheet, which is a low-crystallized polypropylene resin sheet that has been rapidly cooled by the raw fabric sheet manufacturing apparatus, is preheated by preheating rolls 22a and 22b. The preheated original fabric sheet travels from the bottom to the top in the heat treatment tank 23, receives the heat treatment, is cooled by the cooling rolls 24 a and 24 b, and is taken up by the take-up roll 26 through the guide roll 25.
[0024]
Here, the preheating roll 22 is usually preheated to a temperature at which the sheet does not stretch, for example, 40 to 70 ° C., preferably 50 to 60 ° C., using electric heating, heat medium oil, or the like. This preheating temperature is appropriately selected depending on the thickness of the sheet and the traveling speed of the sheet. The preheated raw sheet 11 is introduced upward into the heat treatment tank 23. The heat treatment tank 23 has openings for sheet travel at the upper and lower ends, and the temperature is controlled by the heater 27 so as to heat the internal temperature of the heat treatment tank, that is, the raw sheet 11 at a predetermined temperature.
[0025]
Here, as the heater, electric heating, halogen lamp heating, infrared heating, high frequency heating, hot air, and the like can be employed. If necessary, as shown in FIG. 2, the air in the heat treatment tank can be circulated by the blower 29 and the heated air circulation path 28 to make the temperature distribution in the heat treatment tank uniform. In this embodiment, the temperature control in this case generally controls the temperature of the outlet of the heat treatment tank in the circulation path. In addition, although the case where the heat processing tank was one tank was shown in FIG. 2, it can also be made into the two steps | paragraphs and three steps | paragraphs which use a some tank as needed. In this way, it is possible to individually control the heat treatment temperature of each stage.
[0026]
Here, as heat processing temperature, it can show as air temperature of the heat processing tank 23 in this specification, and it shows as heat processing tank temperature below in this invention. The heat treatment temperature is not particularly limited, but in the case of polypropylene resin, it is usually 70 to 200 ° C, preferably 80 to 180 ° C. This heat treatment temperature is appropriately determined in consideration of the thickness of the raw sheet, the running speed of the sheet, physical properties required for the crystalline thermoplastic resin sheet after the heat treatment, rigidity, transparency, and the like. For example, if it is necessary to increase the rigidity, that is, the elastic modulus, the heat treatment condition is set to the high temperature side, and if the impact resistance is more important than the elastic modulus, the heat treatment condition is set to the low temperature side. Control.
[0027]
After finishing the heat treatment, the sheet exiting the heat treatment tank 23 is cooled by cooling rolls 24a and 24b whose temperature is controlled by water cooling or the like, and a crystalline thermoplastic resin sheet 30 as a product through the guide roll 25. Then, it is wound on the winding roll 26. In addition, if necessary, the processing speed can be increased by providing the cooling air tank 31 on the downstream side of the cooling roll 24.
[0028]
Here, the running speed of the raw sheet in the heat treatment tank 23 varies depending on the production speed of the low crystallization thermoplastic resin sheet, the thickness of the sheet, and the heat treatment temperature, but is usually 5 to 100 m / min. There is a feature that the traveling speed can be greatly increased. Moreover, there is no restriction | limiting in particular as take-up tension | tensile_strength of a sheet | seat, The conditions which a extending | stretching and a deformation | transformation do not arise are set. Usually, the tension is in the range of 10 kg / m width or less.
[0029]
In addition, in FIG. 2, although it is the aspect which performs the heat processing of a sheet | seat after manufacture of an original fabric sheet, the method of paying out and supplying from the roll wound sheet which wound up the original fabric sheet | seat can also be employ | adopted. If the production of the raw sheet and the heat treatment process are separated, the ability of each process may be utilized. Further, the traveling direction of the original fabric sheet can be downward as well as upward.
[0030]
The method for producing a crystalline thermoplastic resin sheet of the present invention is characterized in that the heat treatment tank is changed from a conventional horizontal type to a vertical type, and the raw sheet is run in the vertical direction. That is, as apparent from the examples described later, the width of the heat treatment condition can be greatly changed. In particular, the heat treatment itself was possible even at a heat treatment temperature of 190 ° C., which was significantly higher than around 160 ° C., which is the melting point of polypropylene resin. However, since the transparency of the sheet decreases due to the high-temperature heat treatment, it can be appropriately selected in consideration of other heat treatment conditions such as traveling speed.
[0031]
This leads to a shortening of the heat treatment time, and consequently a significant improvement in the sheet traveling speed and an improvement in productivity. This is related not only to the movement of the original sheet in the vertical direction, but also to the conventional lateral heat treatment tank that requires the sheet to be clamped and run. That is, in order to ensure clamping by the clamp for clamping the sheet, the sheet heating temperature is naturally limited. Furthermore, since the temperature is uniform and there is no fear of sagging due to the weight of the sheet, the present invention can be processed at a high heat treatment temperature.
[0032]
The polypropylene resin sheet obtained in the heat treatment step of the present invention has excellent characteristics not found in conventional polypropylene resin sheets. That is, the polypropylene resin sheet of the present invention is made of polypropylene resin, and (1) both MD and TD tensile elastic moduli are 1500 MPa or more, and ( ² ) the total haze is [300 t ² -150 t + 20 (t is sheet thickness: mm). It is as follows. That is, excellent transparency can be obtained by performing an efficient heat treatment. Depending on the heat treatment conditions, (1) MD and TD tensile elastic modulus and the density thereof are 2000 MPa or more, and the density is 0.905 g / cm ³ or more.
[0033]
Furthermore, since stretching due to drawdown during heat treatment is difficult to occur, the stretching ratio at 90 ° C. in the vertical and horizontal directions is usually within ± 1.0, particularly within ± 0.5. That is, the heat-resistant dimensional accuracy is remarkably improved, and development for heat-resistant applications is possible.
[0034]
【Example】
Hereinafter, although this invention is demonstrated based on the Example of a polypropylene resin, it does not restrict | limit at all to these Examples.
Examples 1-5, Comparative Examples 1-5
Quenched and low-crystallized polypropylene resin sheet (width: 1,000 mm) was produced by the metal belt method and air knife method described in the specification, which are known film forming methods. Table 1 shows the film forming conditions and the properties of the obtained raw sheet. Subsequently, heat treatment was performed under the heat treatment conditions shown in Table 1 to produce a polypropylene resin sheet. The polypropylene resin used for the production of the raw fabric sheet was a propylene homopolymer having a melt index (MI: 230 ° C., 2.16 kg load) of 2.3 g / 10 min. The heat treatment temperature was measured at the outlet of the air circulation channel of the heat treatment tank (heater: infrared heater). The heat treatment tank height was 5 m, and the running speed was 10 m / min.
[0035]
The evaluation results of the obtained sheet are shown in Table 2. In addition, each evaluation was measured according to the following test method.
(1) Density: compliant with JIS K7112 (density gradient tube method) (2) Tensile modulus: compliant with JIS K7113 (3) Haze: compliant with JIS K7105 (4) Glossiness: compliant with JIS K7105 (5) Impact strength : Conforms to JIS K7124 [0036]
[Table 1]

[0037]
[Table 2]

[0038]
【The invention's effect】
According to the present invention, as compared with the case of the horizontal heat treatment tank, the heat treatment temperature is high and the temperature is easily uniformized. For this reason, a crystalline thermoplastic resin sheet such as a polypropylene resin having a higher level of transparency, rigidity, and heat-resistant dimensional stability can be obtained. Further, it is indirect heating, and surface characteristics such as generation of scratches on the sheet surface and gloss are good. Furthermore, high-temperature and short-time treatment is possible, productivity is improved, and equipment is simple and economical. Therefore, the obtained sheet | seat, such as a polypropylene resin, is preferably used for a clear box, a clear file, a stationery case, a frame cover, etc.
[Brief description of the drawings]
FIG. 1 shows a schematic view of the main part of a metal belt process used in a method for producing a polypropylene resin sheet.
FIG. 2 shows a schematic view of one embodiment of a heat treatment apparatus used in the method for producing a polypropylene sheet of the present invention.
[Explanation of symbols]
1: Melted sheet resin 2: T die 3: First cooling roll 4: Second cooling roll 5: Metal endless belt 6: Third cooling roll 7: Fourth roll 8: Elastic coating layer 9: Rotating shaft 10: 5th roll 11: Original fabric sheet 21: Raw fabric sheet manufacturing apparatus 22: Preheating roll 23: Heat treatment tank 24: Cooling roll 25: Guide roll 26: Winding roll 27: Heater 28: Heated air circulation path 29: Blower 30: Resin sheet 31: Cooling air tank

Claims (7)

A method for producing a polypropylene resin sheet, comprising subjecting a polypropylene resin sheet low crystallized by rapid cooling to indirect heating treatment by running in a vertical heating tank in the vertical direction. The method for producing a polypropylene resin sheet according to claim 1, wherein the rapid cooling is performed by a metal belt method or a water cooling method. According to claim 1 or 2 crystalline thermoplastic resin sheet manufacturing method according density of low crystallinity polypropylene resin sheet is 0.890 g / cm ³ or less by quenching. The method for producing a polypropylene resin sheet according to any one of claims 1 to 3, wherein the polypropylene resin does not contain a nucleating agent. A polypropylene resin sheet obtained by indirect heating treatment by running a polypropylene resin sheet low crystallized by rapid cooling in a vertical heating tank in the vertical direction,
(1) MD and TD tensile elastic moduli are both 1500 MPa or more, and (2) total haze is [330 t ² −150 t + 20 (t is sheet thickness: mm)] or less. The polypropylene resin sheet according to claim 5, wherein the MD and TD tensile elastic modulus is 2000 MPa or more and the density is 0.905 g / cm ³ or more. The polypropylene resin sheet according to claim 5 or 6, wherein the expansion and contraction rate at 90 ° C in the MD and TD directions is within ± 1.0%.

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