JPH04258612A - Colorless and transparent ion-crosslinked polymer and its production - Google Patents

Abstract

PURPOSE:To obtain a perfectly colorless and transparent thermoplastic ion- crosslinked polymer by using an aromatic vinyl compound, another vinyl compound and zinc diacrylate as a crosslinking component and introducing a metal ion crosslinkage by a one-stage copolymerization process. CONSTITUTION:An ion-crosslinked polymer comprising 50-100wt.% units (A) derived from an aromatic vinyl compound, 0-50wt.% units (B) derived form another vinyl compound and 0.001-1 pt.wt., per 100 pts.wt. total of A and B, units (C) derived from zinc diacrylater, wherein the polymer has a weight- average molecular weight (in terms of polystyrene) of 100000-1000000 as measured by gel permeation chromatography in an ion crosslinkage-free state and a melt tension value of 10-100g as measured with a melt tension tester under conditions of a temperature of 200 deg.C, an extrusion rate of 30mm/min and a linear winding speed of 10-100cm/sec and a total transmittance of 85% or above as measured with a hazemeter.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a colorless and transparent polymer suitable for sheet-like processed products, film-like processed products, particularly uniaxially oriented and biaxially oriented sheets, films, and foamed processed products, and a method for producing the same. It is related to.

0002

BACKGROUND OF THE INVENTION Most biaxially oriented sheets currently on the market are made of polystyrene or polypropylene. These sheets are widely used for food packaging. However, when manufacturing such sheets and films by stretching, the resin in the molten state is handled, which inevitably causes the sheet or film to sag due to its fluidity, resulting in the problem that the product is likely to have uneven thickness. .

In general, it is a well-known method to partially introduce crosslinking into an amorphous polymer such as polystyrene as a method of controlling the viscoelastic properties in a molten state. One method for producing this crosslinked product is to use a peroxide or the like while the polymer is in a solution or molten state, but this method results in a decrease in molecular weight and is difficult to accurately control the amount of crosslinking. Therefore, the best means for producing a crosslinked product is to copolymerize a comonomer that will become a crosslinked product when polymerizing monomers. A common example of this method is to copolymerize divinylbenzene, diacrylate, dimethacrylate, or other difunctional or polyfunctional vinyl monomers with styrene, but in most cases suspension polymerization is It can only be applied when beads obtained after the process are used as they are, or when plates obtained by cast polymerization are used as they are. In this method, no matter how small the amount of polyfunctional vinyl monomer is, when the resulting polymer is thermoplasticized and used for a film or the like, gel-like foreign matter due to insoluble components will always be generated.

A well-known method for solving these problems is to generate ionic crosslinks or metal ion crosslinks. This ionic bond type crosslinking is
This differs significantly from covalent crosslinking in that when the resin becomes fluid at high temperatures, the intermolecular crosslinking properties are reduced, allowing for free thermoplastic processing. A well-known method for producing this ionic bond type crosslinking is to copolymerize a vinyl compound such as styrene or ethylene with methacrylic acid or acrylic acid, and then melt the copolymer using an extruder or the like. in which inorganic or organometallic compounds are mixed,
This is a method of converting the carboxylic acid of the copolymer into a carboxylic acid metal salt. Another method is to copolymerize a vinyl compound with a vinyl monomer having an ester group, such as methyl methacrylate, and then saponify the copolymer with an alkali. For details on these methods, see L. Hollid “Ionic Polymers” Applied Science Publishers Limited London, (L. Hollid
ay “Ionic Polymers”
Applied SciencePublisher
s LTD. , London, (1975)).

[0005]

However, a drawback of such a metal ion crosslinking method is that the resulting polymer does not become colorless and transparent no matter what method is used. Furthermore, in the metallization reaction, unreacted metal compounds and by-product compounds often remain in the polymer, causing problems such as not only color tone but also odor generation. Furthermore, the method of heating and melting the polymer again to perform a metallization reaction leads to a large increase in energy and other costs, and cannot be said to be an advantageous method when carried out industrially.

[0006]

[Means for Solving the Problems] Under these circumstances, the present inventors have developed an ionic crosslinking method that can be obtained by a production method in which metal ion crosslinking is introduced into a polymer such as styrene by a one-step copolymerization method. It was discovered that the polymer was completely colorless and transparent, and the present invention was developed based on this finding. That is, the present invention provides (A) 50 to 10 aromatic vinyl compound units.
0% by weight, (B) 0 to 50% by weight of other vinyl compound units, (C) zinc diacrylate units of (A) and (B) 1
It is an ionically crosslinked polymer consisting of 0.001 to 1 part by weight per 00 parts by weight, and the weight average molecular weight measured by gel permeation chromatography with the ionic crosslinks removed is 100,000 in terms of polystyrene.
~1,000,000, measured using a melt tension tester at a temperature of 200°C and an extrusion speed of 30 mm/min.
, winding wire speed 10 to 100 cm/sec. A colorless and transparent thermoplastic ionic crosslinked polymer and acrylic acid with a melt tension value of 10 to 100 g measured under the conditions of 10 to 100 g and a total light transmittance of 85% or more as measured by a haze meter, and acrylic acid. A transparent homogeneous solution prepared by adding and reacting zinc oxide in an amount equal to or more than 0.5 times the amount of acrylic acid in a mixed solution of dimethylformamide in an amount equal to or more than the same amount, and an aromatic vinyl compound unit or this and one or more other types. The present invention provides a method for producing an ionically crosslinked polymer, which comprises mixing vinyl compound units and radically polymerizing the resulting transparent homogeneous solution.

[0007] Since the polymer obtained by the method of the present invention has high melt tension, it has extremely excellent processing stability at the stage of forming into a sheet and at the stage of uniaxially or biaxially stretching the sheet. is a feature. In addition, the polymer obtained by the method of the present invention can be processed into sheets or films alone, but it can also be blended with other materials such as styrene-butadiene block copolymer in a specific ratio while maintaining transparency.
Sheets and film processed products produced using these methods will be of even higher quality. It can be a particularly useful polymer for shrink label applications.

Typical polymers obtained by the present invention include (A) aromatic vinyl compound units: 50 to 1;
00% by weight (B) Other vinyl compound units: 0 to 5
0% by weight (C) Zinc diacrylate units are (A) and (B) 10
It has a composition of 0.01 to 1 part by weight to 0 part by weight.

[0009] The aromatic vinyl compound unit, which is the component (A) of this polymer, forms the basic skeleton of the polymer that is the object of the present invention, and provides transparency and rigidity of films and sheets, and provides The viscosity is low and the processability is extremely good. Examples of the aromatic vinyl compound unit include styrene, α-methylstyrene, and para-methylstyrene, with styrene being preferred. The content of this aromatic vinyl compound unit is 50 to 100% by weight. Even if the properties of the polymer are changed by copolymerization with other vinyl compound units, if it is less than 50% by weight, the melt fluidity will change and the change in the rigidity of the molded product will be too large.
Undesirable.

Regarding other vinyl compound units, which are component (B) of this polymer, vinyl cyanide compounds such as acrylonitrile and methacrylonitrile are used to improve oil resistance, and methyl acrylate, ethyl acrylate, Acrylic acid esters such as butyl acrylate and 2-ethylhexyl acrylate are used to lower the glass transition temperature of the copolymer, and methyl methacrylate is used to improve the weather resistance and surface hardness of the copolymer. Unsaturated acids or unsaturated acid anhydrides such as acrylic acid, methacrylic acid, and maleic anhydride are used for high-temperature products due to the increase in the glass transition temperature of the copolymer. In either case, the content of component (B) is 50% by weight or less; if it exceeds 50% by weight, the content of component (A) decreases and fundamental properties are lost, which is not preferable.

[0011] The zinc diacrylate unit, which is a crosslinking component of this polymer, is introduced to control the viscosity during melting by ionic crosslinking of the polymer, and it stabilizes sheet extrudability and secondary processability. It plays the role of making things better. Zinc diacrylate unit shown in the following formula 1

001
2]

[Chemical formula 1]

[0013] has an extremely large effect on the melting behavior of the polymer;
A range of parts by weight is appropriate, and a range of 0.01 to 0.8 parts by weight is more preferred. If it is less than 0.001 part by weight, the crosslinking effect will not be clear, and if it exceeds 1 part by weight, the viscosity during melting will be too high, and the surface condition of the molded product will deteriorate. The method for quantifying zinc diacrylate units is based on measuring the zinc content by atomic absorption or fluorescent X-ray method. In this way, the polymer crosslinked by zinc diacrylate units has a high melt tension value (hereinafter referred to as melt tension value).
It is characterized by having the following. The melt tension value of a polymer crosslinked with zinc diacrylate units is 1.5 to 50 times higher than that of a non-crosslinked polymer when measured under the same conditions. be. This melt tension can be measured using a normal melt index measuring device, but
In particular, it is preferable to use a commercially available melt tension tester. In this case, the measured temperature is 180
The temperature range is from ℃ to 240℃.

In order to derive a non-crosslinked product from a polymer crosslinked with zinc diacrylate units, first the crosslinked polymer is
wt% ethylbenzene or methyl ethyl ketone and 5
By dissolving in a mixture of % by weight acetic acid, filtering, precipitating with methanol, drying, dissolving in the above mixture again and precipitating three times, the zinc bound in the polymer is converted into zinc acetate. A method of desorption is used. The degree of decrease in zinc content in the polymer due to this dezincing treatment can be measured by atomic absorption spectrometry or fluorescent X-ray method, and the melt tension value is also the same as that of the polymer obtained when zinc diacrylate was not added in the polymerization process. The melt tension value decreases to the same level as the melt tension value.

The preferred melt tension value of the present invention is:
The measurement temperature was 200℃ using a melt tension tester.
Extrusion speed 30mm/min. , winding speed 10-1
00cm/sec. The value measured under the conditions of 10 to 1
It is in the range of 00g. If it is less than 10 g, the sheet or film will sag due to fluidity, making the product more likely to have uneven thickness. Moreover, if it is 100 g or more, the melt viscosity increases and processability decreases.

[0016] Such a resin contains 50 to 100% by weight of aromatic vinyl compound units and 0 to 100% by weight of other vinyl compound units.
It is obtained by copolymerizing 0.0003 to 1 part by weight of zinc diacrylate units to a total of 100 parts by weight of 50% by weight. A preferred example of the polymerization method in the method for producing the polymer of the present invention is a solution polymerization method using a system containing 0.001 to 10% by weight of dimethylformamide as a solvent. This solution polymerization method may be a batch method or a continuous method, but since it is desirable to reduce the copolymerization distribution of zinc diacrylate units, it is preferable to use a continuous method and a complete mixing type polymerization vessel. In addition to dimethylformamide, aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene, and ketones such as methyl ethyl ketone and methyl isobutyl ketone may be added as polymerization solvents.

Preferred embodiments of the present invention are shown below. Zinc diacrylate used in the production method of the present invention is a uniform, colorless and transparent solution of dimethylformamide. Even when this zinc diacrylate solution is mixed with a polymerization solution for monomers, etc., it is completely uniform and colorless and transparent. It is necessary that there be. Zinc diacrylate is usually a white powder, and even when mixed with vinyl monomers such as styrene, it does not form a uniform solution. Even if a polymerization charge containing a slurry of zinc diacrylate powder is polymerized, zinc diacrylate is hardly contained in the polymer, and furthermore, a cloudy polymer is obtained. In order to make the polymerization charge containing zinc diacrylate colorless, transparent, and uniform, the polymerization charge is prepared in the following order.

1. First, prepare acrylic acid, zinc oxide, and dimethylformamide. 2. Next, a mixed solution of acrylic acid and dimethylformamide in an amount equal to or more than the same mole as the acrylic acid is prepared, and zinc oxide in an amount of 0.5 mole or less relative to the acrylic acid is gradually added thereto while stirring and mixing. The concentration of zinc diacrylate in the colorless and transparent homogeneous solution thus obtained is determined by the amount of zinc oxide added.

3. Next, this dimethylformamide solution of zinc diacrylate is mixed with the polymerization charge. In this case, if the charged liquid separates into two phases or becomes a viscous liquid,
Add dimethylformamide until the charge is completely homogeneous and clear and colorless. To such a uniform, colorless and transparent charging solution, an organic peroxide or an azo compound is added as a polymerization initiator, and if necessary, a chain transfer agent such as octyl mercaptan or α-methylstyrene dimer is added. The polymerization is carried out continuously in a complete mixing type polymerization vessel, and the polymer solution is continuously discharged. Polymerization temperature is 50℃~150℃
℃ range, and the polymer content in the solution discharged from the polymerization vessel is 20 to 80% by weight. A polymerization solution within this range provides a preferred viscosity. The polymer solution discharged from the polymerization vessel is preheated to 200-250°C and immediately heated to 100 Torr.
It is introduced into a devolatilizer whose pressure is reduced to below r. The role of the devolatilizer is to volatilize and separate unreacted monomers and solvents in the polymer solution. Therefore, the temperature is preferably in the range of 200 to 250°C to provide an appropriate solvent viscosity, and the vacuum is 100 Torr or less. degree is necessary. The average residence time in the devolatilizer is 0
．． It takes 5 to 30 minutes. If it exceeds 30 minutes, low molecular weight products will be produced due to polymer chain cleavage, which is not preferable. Also 0
．． If the time is less than 5 minutes, devolatilization will not be sufficient. As a devolatilizer, either a devolatilization tank or an extruder with a vent port can be used. The polymer discharged from the devolatilizer in this way is
It is cooled, solidified, and pelletized to become a product. Through this process, for the first time, a colorless and transparent product with a total light transmittance of 85
A thermoplastic, metal ion crosslinked product having a high melt tension of at least 10% is obtained, which is completely free of gel-like substances.

[0020]

EXAMPLES Next, the present invention will be explained in more detail with reference to Examples. The methods for measuring physical properties in Examples and Comparative Examples are as follows. (1) Sheet extrudability: Measure the thickness unevenness of a 200μ thick sheet extruded from a T-die of a 35m/m extruder. ±
If it is within 10%, it is considered good, and if it is more than 10%, it is considered bad. (2) Film stretchability: A 200μ sheet was stretched in two axial directions using a batch tenter, and the stretching uniformity was checked. (3) Vicat softening point temperature: ASTM D-1525
(4) Notched Izod test: ASTM D-25
6 (5) Bending strength, bending modulus: ASTM D-79
0-71 (6) Melt tension test: A melt tension tester type II manufactured by Toyo Seiki Seisakusho was used. 200℃,
Extrusion speed: 20 mm/min, winding speed: 13 cm/sec. (7) Total light transmittance: ASTM sample with a thickness of 2.5 mm
Measured according to D-1003.

Preparation of a solution of zinc acrylate. 72.06 g of acrylic acid and 110 g of dimethylformamide
．． Mix 76g. This mixed solution is put into a stainless steel reactor, and the outside is cooled with cooling water at 10°C. A total of 40.69 g of powdered zinc oxide is gradually introduced into the reactor, but the internal temperature is not allowed to exceed 30°C. After the addition of zinc oxide is completed, stirring is continued for about 3 hours, and then the solution is stored in a cool, dark place. This solution is almost colorless and transparent, but if there is some cloudiness, filter it with a glass filter. The composition and properties of the obtained solution are as follows.

Zinc acrylate: 94.73g (
42.4% by weight) H2O
: 18.02g (8.0% by weight) Dimethylformamide: 110.76g (49.6% by weight)
d425: 1.
206 Viscosity:
16.2 centipoise (25℃) Properties
: Colorless transparent liquid

002
3]

[Example-1] 100 parts by weight of a mixed solution of 80% by weight of styrene and 20% by weight of n-butyl acrylate, 7 parts by weight of dimethylformamide, and 0 parts by weight of zinc diacrylate solution.
．． 1 part by weight, 1,1-di-t-butylperoxy-3,
A polymerization solution containing 0.02 parts by weight of 3,5-trimethylcyclohexane is prepared. This polymerization solution was continuously charged into a 2.0 liter complete mixing type polymerization vessel at a rate of 0.345 (l/hr). The polymerization temperature was 110°C,
The polymer content in the polymer solution continuously discharged from the polymerization vessel was 52% by weight. This solution is introduced into a single-screw extruder heated to 230° C. and has a vent port with a reduced pressure of 20 Torr, and after devolatilization, it is solidified and pelletized. The solution discharged from the polymerization vessel was made into a low-viscosity solution with dimethylformamide, precipitated with methanol, and after drying, dissolution, precipitation, and drying were repeated three times in total, and the amount of zinc in the purified polymer was measured by atomic absorption spectrometry. As a result of measurement, it was 0.026% by weight, and therefore, it can be considered that the entire amount of zinc diacrylate was converted into a polymer. On the other hand, based on the refractive index of the polymer, the content of n-butyl acrylate units in the polymer was 18.1% by weight. The polymer composition is as follows.

[0024] Styrene unit: Ba
lance n-butyl acrylate unit: 18.
1% by weight zinc diacrylate unit: 0.
The properties of the 076% by weight polymer are listed in Table 1.

[0025]

Comparative Example 1 A polymer was obtained by polymerizing under the same conditions as in Example 1, except that the zinc diacrylate solution was not added to the polymerization solution. The composition of the polymer was 81.5% by weight of styrene units and 18.5% by weight of n-butyl acrylate units. The properties of the polymer are listed in Table 1.

[0026]

[Example 2] Polymerization was carried out under the same conditions and in the same manner as in Example 1, except that n-butyl acrylate was not added to the polymerization solution and 100 parts by weight of styrene was used to obtain a polymer. . Polymer composition: Styrene unit: 99.92% by weight Zinc diacrylate unit: 0.080% by weight
Met. The properties of this polymer are listed in Table 1.

[0027]

[Comparative Example-2] In Example-1, styrene was used alone without adding n-butyl acrylate and zinc diacrylate solution to the polymerization solution, and the polymerization was carried out under the same conditions and in the same manner to obtain a polymer. Ta. The properties of this polymer are listed in Table 1.

[0028]

[Examples 3 and 4, Comparative Examples 3 and 4] Examples 1 and 2
, the polymers obtained in Comparative Examples -1 and -2; 50% by weight, styrene (70% by weight) manufactured by Asahi Kasei, and butadiene (30% by weight).
Asaflex 8, a block copolymer of
10; 50% by weight was kneaded using a 35 m/m twin screw extruder as shown in Table 2. The resulting blend is transparent.

Its properties are listed in Table 3.

[0030]

[Example-5] In Example-1, 0.35 parts by weight of zinc diacrylate solution was added to 100 parts by weight of a mixture of 32.3% by weight of styrene, 33.7% by weight of acrylonitrile, and 34.0% by weight of ethylbenzene. Except for the parts by weight,
Polymerization was carried out under the same conditions and by the same method to obtain polymers. The properties of this polymer are listed in Table 4.

[0031]

[Comparative Example 5] In Example 5, the zinc diacrylate solution was not added to the polymerization solution, and the polymerization was carried out under the same conditions and in the same manner except that a polymer was obtained. The properties of this polymer are shown in Table 4.
It is written in

[0032]

[Example-6] In Example-1, the polymerization solution was 10% by weight of a mixture of 50% by weight of styrene and 50% by weight of methyl methacrylate.
Polymerization was carried out under the same conditions and in the same manner except that 7 parts by weight of dimethylformamide and 0.16 parts by weight of zinc diacrylate solution were used to obtain a polymer. The properties of this polymer are listed in Table 4.

[0033]

[Comparative Example 6] In Example 6, the zinc diacrylate solution was not added to the polymerization solution, and the polymerization was carried out under the same conditions and in the same manner, to obtain a polymer. The properties of this polymer are shown in Table 4.
It is written in

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

[0037]

[Table 4]

[0038]

Effects of the Invention The ionically crosslinked polymer obtained by the production method of the present invention in which metal ion crosslinking is introduced by a one-step copolymerization method is colorless and transparent, and is suitable for use in sheet-like processed products, film-like processed products, especially uniaxially processed products. Stretched, biaxially oriented sheets, films,
It is also a suitable polymer for foamed products.

Claims (3)

[Claims] Claim 1: (A) 50 to 10 aromatic vinyl compound units
0% by weight, (B) 0 to 50% by weight of other vinyl compound units, (C) zinc diacrylate units of (A) and (B) 1
It is an ionically crosslinked polymer consisting of 0.001 to 1 part by weight per 00 parts by weight, and the weight average molecular weight measured by gel permeation chromatography with the ionic crosslinks removed is 100,000 in terms of polystyrene.
~1,000,000, the melt tension value measured by a melt tension tester at a measurement temperature of 200 ° C., an extrusion speed of 30 mm/min, and a winding wire speed of 10 to 100 cm/sec is 10 to 100 g, and a haze meter A colorless and transparent thermoplastic ionically crosslinked polymer having a measured total light transmittance of 85% or more. 2. The aromatic vinyl compound unit is styrene, and the other vinyl compound unit is any one of n-butyl acrylate, acrylonitrile, methyl methacrylate,
or a combination thereof. 3. A transparent homogeneous solution prepared by adding and reacting zinc oxide in an amount equal to or more than 0.5 times the mole of acrylic acid to a mixed solution of acrylic acid and dimethylformamide in an amount equal to or more than the same mole relative to the acrylic acid; 3. The method for producing a polymer according to claim 1, wherein the aromatic vinyl compound unit or the aromatic vinyl compound unit is mixed with one or more other vinyl compound units, and further radical polymerization is carried out to form a transparent homogeneous solution.