JP4041885B2 - High strength and high transparency polypropylene sheet and method for producing the same - Google Patents

Description

【００１８】
【発明の効果】
本発明で得られるアイソタクチックポリプロピレンシートは、結晶性で、かつ、シート厚さがおおきいにもかかわらず、透明性に優れたものであり、「弾性率1.2GPa以上、破断強さが90MPa以上であり、ヘーズ値が11％以下であり、成形されているアイソタクチックポリプロピレンシート」（機械特性が高いもの）が得られる。
又、本発明のアイソタクチックポリプロピレンシートの製造方法によれば、特定の結晶核剤を添加するので、圧延倍率の高い条件下に圧延することができること、又、高い圧延倍率の場合にはヘーズ値が低いものが得られるものである。
【図面の簡単な説明】
【図１】圧延倍率と平均圧延圧力の関係を示す図
【図２】圧延倍率とへーズ値の関係を示す図[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a transparent isotactic polypropylene sheet having a mechanical strength and a method for producing the same. This isotactic polypropylene sheet can be used as, for example, various sheets such as a binding tape, a heavy wrapping sheet, a stationery sheet, a file case, and cards.
[0002]
[Prior art]
A highly transparent film can be obtained by stretching an unoriented film such as polyolefin or polyester (Patent Document 1). However, in the stretching process, even if the processing is successful in the case of a relatively thin film, the thick sheet is deformed unevenly and it is difficult to obtain a transparent sheet with a good surface condition. It was. For this reason, it is required to stretch after the rolling process and to perform heat treatment before the stretching (Patent Document 2). A thick sheet is rolled to bring an orientation effect (Patent Document 3). The operation requires a relatively complicated operation. However, usually a large rolling reduction force is required, there are restrictions on the equipment, and an excessive load is applied to the material surface during processing, so that a sufficiently good surface state and transparency cannot be obtained. there were. Furthermore, in order to increase the rigidity of a crystalline resin sheet having a low degree of crystallinity, an annealing treatment in which the resin sheet is directly heated at a specific temperature or indirect heating is performed (Patent Document 4).
Isotactic polypropylene has a density of 0.91 g · cm ⁻³ , the smallest among plastics, and has superior mechanical properties compared to polyethylene. It has translucent properties and favorable characteristics as a sheet such as high surface hardness and resistance to damage (Non-Patent Documents 1 to 3). Focusing on this excellent characteristic, it is desired to make the material more preferable in terms of elastic modulus, breaking strength, and haze value, and further to make the material transparent.
Even if the conventionally known molding process conditions are applied to this isotactic polypropylene, a desired material cannot be obtained.
[0003]
[Patent Document 1]
JP 10-329207 A
[Patent Document 2]
JP 10-272687 A
[Patent Document 3]
Shoko 55-31725
[Patent Document 4]
JP 10-217342 A
[Non-Patent Document 1]
Daiki Michinori et al., Chemistry Dictionary 1998 ・ 6.1, published by Tokyo Chemical Dojin Co., Ltd., page 2251
Kurihara Fukuji, Encyclopedia of Polymer Materials, 1999/7/30 Nikkan Kogyo Co., Ltd., 205 pages [Non-patent Document 3]
Polymer Handbook 4th edition 1999 John Wiley & Sons, Inc. Issue v / 21 ~ V / 28, V / 160
[0004]
[Problems to be solved by the invention]
An object of the present invention relates to a sheet of isotactic polypropylene, has transparency and has a mechanical strength, it is to provide a method for producing superior wood charge.
[0005]
[Means for Solving the Problems]
The present invention has been completed as a result of intensive studies to solve the above problems. That is, according to the present invention, when a specific crystal nucleating agent is added to isotactic polypropylene and then melted, cooled, crystallized and rolled under specific conditions, it can be rolled under conditions with a high rolling ratio. The inventors have found that a low haze value can be obtained in the case of a high rolling ratio, and found that the above problems can be solved, thereby completing the present invention.
Specifically, after blending a specific crystal nucleating agent with isotactic polypropylene, it is melt-extruded from a T die into a sheet, and when the melting point of the polypropylene is Tm, (Tm−90) ° C. or higher, (Tm -40) Crystallization is performed on the surface of a chill roll having a temperature of not higher than ° C to obtain a sheet made of isotactic polypropylene.
This sheet is rolled in a temperature range of (αc−30) ° C. to (αc + 20) ° C., where αc is the crystal dispersion peak temperature of the loss factor in the non-resonant forced vibration method dynamic viscoelastic temperature curve with a frequency of 1 Hz. By doing so, it is possible to obtain a sheet made of isotactic polypropylene having an elastic modulus of 1.2 GPa or more, a maximum stress of 90 MPa or more, a haze value of 11% or less, transparency, and excellent mechanical properties. As a result, the present invention has been completed.
[0006]
According to the present invention, the following inventions are provided.
A isotactic polypropylene blended with nucleating agent, through a T-die, a sheet form melt extrusion of a thickness of less than 5mm above 1.2 mm, when the melting point of the polypropylene was Tm, at (Tm-90) ℃ or higher When a sheet is produced by crystallization on the surface of a chill roll having a temperature of (Tm-40) ° C. or lower, and the crystal dispersion peak temperature of the loss coefficient in the non-resonant forced vibration method dynamic viscoelastic temperature curve at a frequency of 1 Hz is αc. to, (αc-30) with (αc + 20) temperature range ° C. from ° C., and rolling the unoriented sheet of length _{L 1,} when the length _{L 2,} the rolling ratio λ _{(= L} 2 / L ₁ ) Is rolled under a condition of 2.3 or higher, is transparent, has an elastic modulus of 1.2 GPa or higher, a breaking strength of 90 MPa or higher, and a haze value of 11% or lower. Made Isotactic polypropylene sheet manufacturing method, characterized by.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Isotactic polypropylene is used as the material for the film of the present invention. In addition to powdered isotactic polypropylene obtained from the production process, pellet-shaped isotactic polypropylene can be used. Untreated isotactic polypropylene is translucent and has low mechanical strength.
[0008]
In the present invention, a crystal nucleating agent is added to isotactic polypropylene in powder or pellet form.
Crystal nucleating agents include sorbitol compounds, rosin compounds, benzoate compounds, and organic phosphate compounds, and any of these may be used.
Examples of the sorbitol compound include dibenzylidene sorbitol and bis (4-ethylbenzylidene sorbitol).
Examples of rosin compounds include dihydroabietic acid metal salts.
Examples of the benzoate-based compound include hydroxy-di- (4-tert-butylbenzoate) aluminum.
Examples of the organic phosphate compound include bis (4-tert-butylphenol) acid phosphate sodium salt and methyl bis (2,4-tert-butylphenol) acid phosphate sodium salt.
These crystal nucleating agents are used in powder form, and are blended in a weight ratio of 0.1% to 1%, preferably 0.3% to 0.8% with respect to the pellets.
[0009]
A melting treatment is performed in a state where a crystal nucleating agent is mixed with pellet-like or powder-like isotactic polypropylene.
The melting temperature is set to a temperature equal to or higher than the melting point.
The heating temperature is set to a temperature of 160 ° C. or higher, which is the melting point of isotactic polypropylene. Normally, a melting point of 40 ° C. or higher is employed. The upper limit is appropriately set in consideration of the thermal decomposition temperature. It is not necessary to set the temperature higher than necessary.
Conditions used in normal plastic processing are employed for the melting operation. A screw kneader is used as the melting device. It has a twin screw extruder and has heating means so that it can be melted by heating.
Isotactic polypropylene pre-blended with a crystal nucleating agent is supplied from a hopper.
After melt-kneading, it is melt-extruded in a sheet form from a T die.
[0010]
After melt-kneading, the isotactic polypropylene sheet melt-extruded from the T die into a sheet is guided onto a roll, cooled and crystallized.
The set temperature is a temperature of (Tm−90) ° C. or more and (Tm−40) ° C. or less when the melting point of polypropylene is Tm. The temperature at which the product obtained by melt-kneading is cooled and crystallized is not in a special range. If it is below this temperature range, sufficient crystal growth will not occur, and if it exceeds this temperature range, solidification will be slow and sheet molding will be difficult.
Although the thickness of the sheet obtained in this state can be selected as appropriate, it is generally 1.2 mm or more, and the upper limit can be selected as appropriate.
[0011]
The sheet is rolled. In this rolling process, it is important to control the temperature at which temperature is to be processed.
In the present invention, isotactic polypropylene is expressed as follows: “(αc−30) ° C. to (αc + 20) where αc is the crystal dispersion peak temperature of the loss coefficient in the non-resonant forced vibration method dynamic viscoelastic temperature curve with a frequency of 1 Hz. Rolling is performed at a temperature range of ° C.
"Non-resonant forced-vibration dynamic viscoelastic temperature curve with 1 Hz frequency" is a measurement of the distortion as a response when a sine wave stress with a frequency of 1 Hz is applied to a sheet as a sine wave. This is a curve obtained by plotting the dynamic elastic modulus obtained from the amplitude and the loss coefficient tan δ obtained from the stress and strain phase angle δ with respect to the measurement temperature, and is usually measured by a dynamic viscoelasticity measuring apparatus in a tensile mode.
“Loss coefficient” represents the degree of molecular motion of a polymer.
“Crystal dispersion peak temperature” means “temperature at which slippage of molecular chains in the crystal region becomes active”.
After all, the above-mentioned “temperature range from (αc−30) ° C. to (αc + 20) ° C.” when the crystal dispersion peak temperature of the loss coefficient in the non-resonant forced vibration method dynamic viscoelastic temperature curve with a frequency of 1 Hz is αc. Can be said to be a good range because the polypropylene crystal itself deforms. Processing at this level is not a specific temperature range as the temperature of the polypropylene rolling method.
In the embodiment, αc is 110 ° C.
In the rolling process of the present invention, a deformation with a rolling magnification (λ) of 2.3 times or more, preferably λ of 4 or more is given. Specifically, it means that when an unoriented sheet having a length L ₁ is rolled to a length L ₂ , the rolling magnification λ (= L ₂ / L ₁ ) is 2.3 or more.
When rolled under such conditions, the molecular chains can be highly oriented.
[0012]
With respect to the specific temperature range, it is applied to the “isotactic polypropylene sheet formed by blending the crystal nucleating agent” defined in the present invention, so that the microscopicity of the polypropylene sheet crystallized by mixing the crystal nucleating agent is obtained. Spherulites can be subdivided into finer lamellar crystals by rolling operation.
In normal thin film forming, when a crystal nucleating agent is blended and formed, many fine spherulites are formed, less visible light is scattered, and transparency is usually obtained. This is not the case with material sheets. That is, the laminated structure of the fine spherulites in the thickness direction scatters visible light, resulting in insufficient transparency.
The thick sheet formed by blending the crystal nucleating agent of the present invention has excellent transparency despite the large sheet thickness. It is considered that it is subdivided into a lamellar crystal having a thickness of nanometer and visible light is no longer scattered.
Furthermore, in rolling a sheet crystallized with a crystal nucleating agent, the average rolling pressure is kept low due to crystal slippage during rolling, and molecules are oriented without difficulty and the occurrence of voids is also suppressed. It is considered that excellent transparency can be imparted.
In addition, the reason why the sheet of the present invention exhibits high breaking strength is that the crystal chains are highly arranged and the amorphous chains are also highly arranged, and a structure with few defects such as voids can be imparted. It is done. That is, a thick “isotactic polypropylene sheet” having transparency, mechanical strength and mechanical properties obtained by the present invention could be obtained by adding a “crystal nucleating agent”. This is considered to be due to the rolling operation of the isotactic polypropylene sheet "molded under specific temperature conditions.
In the method according to the present invention, since the crystal nucleating agent is blended, it can be rolled even at a low average rolling pressure (FIG. 1), and it can be rolled to a high rolling ratio (FIG. 1). . Furthermore, in rolling a crystallized sheet containing a crystal nucleating agent, during rolling, the average rolling pressure is kept low due to slipping of the crystals, and molecules can be oriented without difficulty. Is also suppressed, and a good value is obtained (FIG. 1).
Further, as described above, it is preferable that the rolling ratio can be increased, but it can be seen that a haze value can be reduced by increasing the rolling ratio (FIG. 2).
Table 1 shows the results of a tensile test of the obtained sheet at 23 ° C. It can be seen that both strength and elastic modulus are greatly improved by the rolling operation.
[0013]
According to the present invention, a “formed isotactic polypropylene sheet having an elastic modulus of 1.2 GPa or more, a breaking strength of 90 MPa or more, and a haze value of 11% or less” can be obtained. In Example 1, when rolling was performed in the uniaxial direction under a condition where the rolling magnification (λ) was 7.6 times, a sheet having a good surface state and good transparency could be obtained. The breaking stress in the direction was 370 MPa, and the elastic modulus was 3.55 GPa.
In the present invention, since a crystal nucleating agent is used, a high rolling ratio can be adopted. As a result, it can be performed even at a low value as the average rolling pressure, and the rolling ratio can be increased. Obtainable.
The isotactic polypropylene sheet of the present invention having the above properties can be advantageously used as a material for processing various sheets such as a binding tape, a heavy packaging sheet, a stationery sheet, a file case, and cards.
[0014]
【Example】
Next, the present invention will be described in more detail with reference to examples. The present invention is not limited to this.
[0015]
Example 1
As raw isotactic polypropylene, pellets of Chisso PP K1011 manufactured by Chisso Petrochemical were used. Dihydroabietic acid metal salt (KM1500 manufactured by Arakawa Chemical Industries, Ltd.), which is a rosin crystal nucleating agent, was used as the crystal nucleating agent.
A chill roll set to 80 ° C., containing 0.3% by weight of a crystal nucleating agent in the polypropylene pellets, heated and melted and kneaded at 240 ° C. with a twin screw extruder, extruded from a T-die having a width of 60 mm and a gap of 2 mm into a sheet. And wound up after the crystallization and cooling operations.
The crystal dispersion peak temperature αc of the loss factor in the non-resonant forced vibration method dynamic viscoelasticity temperature curve of the frequency of 1 Hz of the sheet having a thickness of about 1.5 mm thus obtained was 120 ° C.
When this sheet was rolled with a rolling roll heated to a predetermined temperature (110 ° C.) at a rolling magnification (λ) of 7.6 times in a uniaxial direction, the surface state was good and a transparent sheet could be obtained. .
The film had a breaking stress in the longitudinal direction at 23 ° C. of 370 MPa and an elastic modulus of 3.55 GPa. The haze value was 2.7%.
[0016]
Example 2
In Example 1, the relationship between the average rolling pressure and the rolling ratio at the time of rolling was measured under the condition that the rolling ratio of the polypropylene sheet was changed, and the result is shown in FIG.
As a comparative example, the average rolling pressure of the polypropylene sheet when no crystal nucleating agent is blended is also shown. When the rolling ratio is increased, the average rolling pressure can be rolled at a lower value than expected. Also, comparing the comparative example and the example,
When the crystal nucleating agent is blended (Example), it is shown that the average rolling pressure can be performed with a smaller value than when the crystal nucleating agent is not blended (Comparative Example). That is, in the method according to the present invention, it can be seen that the average rolling pressure can be performed at a low value, and that rolling can be performed up to a high rolling ratio.
FIG. 2 shows the relationship between the haze value of the rolled sheet and the rolling ratio. As a comparative example, a case where neat polypropylene not containing a crystal nucleating agent was used was shown. It shows that the haze value can be lowered when the rolling ratio is increased. Further, in the case of using the isotactic polypropylene of the present invention (Example), it is shown that a sheet having a low haze value can be obtained as compared with the case of using neat polypropylene.
Furthermore, Table 1 shows the results of a tensile test of the obtained sheet at 23 ° C. It can be seen that when the rolling ratio is increased, both strength and elastic modulus are greatly improved accordingly.
[0017]
[Table 1]

[0018]
【The invention's effect】
The isotactic polypropylene sheet obtained by the present invention is crystalline and has excellent transparency despite its large sheet thickness, “elastic modulus 1.2 GPa or more, breaking strength 90 MPa or more Thus, a molded isotactic polypropylene sheet (having high mechanical properties) having a haze value of 11% or less is obtained.
Further, according to the method for producing an isotactic polypropylene sheet of the present invention, since a specific crystal nucleating agent is added, it can be rolled under a condition with a high rolling ratio, and in the case of a high rolling ratio, haze A low value is obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing the relationship between rolling ratio and average rolling pressure. FIG. 2 is a diagram showing the relationship between rolling ratio and haze value.

Claims (1)

A crystal nucleating agent is blended with isotactic polypropylene, melt-extruded from a T die into a sheet having a thickness of 1.2 mm or more and 5 mm or less, and when the melting point of polypropylene is Tm, (Tm-90) ° C. or more, When a sheet is produced by crystallization on the surface of a chill roll at a temperature of (Tm-40) ° C. or lower, and the crystal dispersion peak temperature of the loss coefficient in the non-resonant forced vibration dynamic viscoelastic temperature curve at a frequency of 1 Hz is αc. When a non-oriented sheet having a length L ₁ is rolled to a length L ₂ in a temperature range from (αc-30) ° C. to (αc + 20) ° C. , the rolling magnification λ (= L ₂ / L ₁ ) An isotactic polypropylene sheet formed by rolling under a condition of 2.3 or higher, transparent, having an elastic modulus of 1.2 GPa or more, a breaking strength of 90 MPa or more, and a haze value of 11% or less. Made Isotactic polypropylene sheet manufacturing method, characterized by.

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