JPH08318567A - Manufacture of polymer film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a low density polymer film excellent in flexibility, heat stability, antistatic characteristics and production aptitude and suitable as a paper substitute. SOLUTION: A polymer film producing method has a process (i) for producing a polymer resin sheet containing a styrene resin and a polyester resin which contains metal sulfonate, a process (ii) for longitudinally stretching the obtained polymer resin sheet, a process (iii) for laterally stretching the obtained longitudinally stretched polymer resin sheet and a process (iv) for heat-treating the obtained biaxially stretched film. The processes (iii), (iv) are performed under a condition satisfying formulae Tg+20<Ts<Tg+60, 80<Th-Ts<110 and 4<(Th-Ts)/t<30 [wherein Tg is a glass transition temp. ( deg.C) of a polyester resin, Ts is a temp. ( deg.C) in the lateral stretching process, Th is heat treatment temp. and t is a heat treatment time (sea)].

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a polymer film, and more specifically, a low density polyester-polystyrene having excellent antistatic properties, printability and flexibility, which is useful as a substitute for paper. Regarding film.

[0002]

2. Description of the Related Art Polyolefin films containing inorganic particles are used as a substitute for paper in calendars, advertising papers, high-grade packaging materials and the like. However, recently, polyolefin films are being replaced by polyethylene films that have high mechanical strength, heat resistance, durability and dimensional stability. However, such polyester films are still inferior to paper in transparency, color, hardness and density.

Extensive attempts have been made to develop low density polyesters that have paper-like flexibility while retaining other desirable properties. For example, JP-A-62-24
3120 and JP-A-2-206622 describe mixing inorganic particles into a polyester film. JP-A-58-50625 describes a method for producing a low density polyester film by incorporating a foaming agent. Further, JP-A-57-49648 discloses that a polyolefin resin is blended with a polyester resin, and the blend is stretched to form fine pores on the surface and inside of the resulting film, thereby improving low surface properties. A method of making a density polymer film is provided.

However, the polyester film disclosed in the above-mentioned references has the following problems. Incorporation of large amounts of inorganic particles in polyester films increases their density to undesired levels.
When a polyester film is mixed with a blowing agent, the microbubbles formed tend to disperse non-uniformly, which makes it difficult to control the physical properties of the film. Further, when a polyolefin resin is blended with a polyester resin, the properties of the resulting polymer film may be degraded in some cases due to undesirable properties of the polyolefin component, such as poor heat resistance.
Polyester-polyolefin films are also highly static and less printable because polyolefins tend to generate and accumulate static electricity, which limits the use of films as paper substitutes and magnetic recording media. In addition to these, since the method of the prior art simply mixes the polyolefin and the polyester resin in a dry state, there is a problem that the obtained film easily breaks and the thickness becomes uneven.

[0005]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide improved flexibility, good thermal stability, excellent antistatic properties by carrying out the stretching and heat treatment steps under the conditions specified in the present invention. It is an object of the present invention to provide a method for producing a low density polymer film which has properties and printability and is suitable for use as a paper substitute.

[0006]

According to the present invention, (i)
Styrene resin containing 60% by weight or more of styrene monomer unit based on the weight of styrene resin and 1.0
a step of producing a polymer resin sheet containing a polyester resin containing a sulfonic acid metal salt having an acid value of mgKOH / g or less; (ii) a step of stretching the obtained polymer resin sheet in the longitudinal direction; (iii) In the method for producing a polymer film, which comprises the step of stretching the longitudinally stretched polymer resin sheet in the transverse direction; and (iv) the step of heat-treating the obtained biaxially stretched film, wherein (iii) and (iv)
The method of producing a polymer film, wherein the step of is performed under conditions satisfying the following formula.

Tg + 20 <Ts <Tg + 60 (1) 80 <Th-Ts <110 (2) 4 <(Th-Ts) / t <30 (3) In the formula, Tg is the glass transition temperature (° C.) of the polyester resin; Ts is the temperature (° C.) at which the transverse stretching step is performed; Th
Is the heat treatment temperature (° C.); t is the heat treatment time (seconds).

[0008]

According to the present invention, after heating a polystyrene-polyester resin mixture containing a sulfonic acid metal salt at a temperature higher than the melting point of the polyester resin,
The obtained homogeneous resin mixture is extruded on a cooling drum having a die to obtain an amorphous sheet. The obtained amorphous sheet is passed through a roller and stretched at a stretching ratio of 2 to 4 along the traveling direction, that is, the longitudinal direction of the film. The longitudinal stretching is preferably performed at a temperature in the range of Tg + 10 ° C to Tg + 50 ° C. Here, Tg is the glass transition temperature of the polyester resin, for example, in the range of 70 to 80 ° C. Preferably, the stretched sheet is gradually cooled to room temperature.

After stretching in the machine direction, the film is transferred to a tenter, and both ends of the film are held by, for example, clips to stretch the film in the transverse direction. The stretching temperature in the transverse direction is preferably Tg + 20 ° C. to Tg + 6 represented by the formula (1).
It is in the range of 0 ° C. If the transverse stretching temperature Ts is Tg + 20 ° C. or less, the defective product occurrence rate increases such as breakage, and T
When the temperature is g + 60 ° C. or higher, the number of pores formed inside the film is reduced, and as a result, the density of the film is increased.

The resulting biaxially stretched film is represented by the formula (1),
Heat treatment was performed under the conditions satisfying (2) and (3) to obtain 0.
A film having a bulk density of 8-1.3 g / cm ³ is obtained.

Tg + 20 <Ts <Tg + 60 (1) 80 <Th-Ts <110 (2) 4 <(Th-Ts) / t <30 (3) In the formula, Tg is the glass transition temperature (° C.) of the polyester resin; Ts is the temperature (° C.) at which the transverse stretching step is performed; Th
Is the heat treatment temperature (° C.); t is the heat treatment time (seconds).

The heat treatment temperature is Th-Ts of 80 ° C. to 110 ° C.
Control so that the temperature is in the range of ° C. This is because when Th-Ts is 80 ° C. or less, the dimensional stability of the obtained film becomes poor, and when it is 110 ° C. or more, the heat treatment at high temperature destroys the pores in the film, resulting in the density of the resulting film. Is higher. Furthermore, even when the heat treatment temperature satisfies the expression (2), the heat treatment time is (Th-T
Control is performed so that s) / t falls within the range of 4 to 30. This is because when (Th-Ts) / t is 4 or less, the dimensional stability of the obtained film becomes poor, and when it is 30 or more, the density of the obtained film becomes high.

The polyester which can be used in the present invention is 0.10 per 25 ml of orthochlorophenol.
When measured at a temperature of 35 ° C. at a concentration of 3 g, 0.4-
It has an intrinsic viscosity in the range of 0.9 dl / g, preferably 0.5-0.7 dl / g. The polyester can be produced by polycondensing an acid component such as a dialkyl ester of an aromatic dicarboxylic acid and a diol component such as an aliphatic glycol.

Representative dialkyl esters of aromatic dicarboxylic acids that can be used in the present invention include:
Dimethyl terephthalate, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid, diphenoxyethanedicarboxylic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, anthracenedicarboxylic acid and α, β-bis (2-chlorophenoxy) ethane-4, 4'-dicarboxylic acid and the like. Of these, dimethyl terephthalate and terephthalic acid are most preferred.

Typical examples of the aliphatic glycol which can be used in the present invention include ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol and hexylene glycol. Of these,
Most preferred is ethylene glycol.

The polyester of the present invention comprises at least 70
It contains a weight percentage of a homopolymer of polyethylene terephthalate, the balance being other copolymer units. The copolymer component is a diol compound such as diethylene glycol, propylene glycol, neopentyl glycol,
Polyethylene glycol, p-xylene glycol,
With 1,4-cyclohexanedimethanol and 5-sodium sulforesorcin; polycarboxylic acids such as trimellitic acid and pyromellitic acid.

The antistatic agent that can be incorporated into the polymer resin of the present invention is a sulfonic acid metal salt of the formula (4) having an acid value of 1.0 mgKOH / g or less.

R ₁ —SO ₃ Me (4) In the formula, R ₁ is a C ₅ -C ₂₀ alkyl group, and Me is L
i, Na, K or Mg.

Suitable metal sulfonates include potassium octylbenzene sulfonate, potassium nonylbenzene sulfonate, potassium undecyl benzene sulfonate and mixtures thereof. Incorporation of such metal sulfonates provides the film with good antistatic properties and also increases the surface tension of the film, thereby reducing the loss of information on the magnetic card, inks and other coating compositions. Improve the acceptability of.

The metal sulfonic acid salt is added in an amount in the range of 0.01 to 1.0% by weight, preferably 0.02 to 0.5% by weight, based on the weight of the polyester resin. If it is less than 0.01% by weight, fine bubbles are generated on the surface of the film and the physical properties of the film are significantly deteriorated, and the effect of improving the antistatic property is small, and more than 1.0% by weight. This is because the polyester is decomposed and the mechanical properties of the film are significantly reduced.

The polyester resin used in the production of the polymer film of the present invention contains other additives such as polycondensation catalysts, dispersants, other antistatic agents, crystallization accelerators, nucleating agents and antiblocking agents. It may be included in an effective amount that does not adversely affect the desired properties of the film of the present invention. In addition to this, an inorganic filler selected from barium sulfate, titanium dioxide, silicon dioxide, calcium carbonate, magnesium oxide, talc and mixtures thereof is added in an amount of 20% by weight or less based on the weight of the polyester resin. Good. If the amount added exceeds 20% by weight, the mechanical properties of the film will deteriorate and a low density film cannot be obtained.

When a resin mixture of polystyrene and polyester is extruded and stretched to form a film, 2
Due to the incompatibility of the two resins, micropores are formed on the surface and inside the film, which gives the film improved surface properties and low density.

However, the size and distribution of such micropores is critical in determining other properties of the film, and the method of the present invention produces uniform size microfeatures in and on the film. It provides a means of uniform dispersion, which gives the film improved mechanical properties and processability in addition to improved surface properties and low density.

A preferred styrene resin that can be mixed with the polyester resin of the present invention is at least 60 wt%.
Of polystyrene with the balance being other copolymer units. The copolymer component is acrylonitrol, butadiene, or the like.
The styrene resin used in the present invention is 1.0 to 2
It has a melt flow index (melt flow rate) of 5 g / 10 min (200 ° C., 5.0 kg filling), preferably 2.5 to 15 g / 10 min. The styrene resin can be mixed in an amount of 5 to 35% by weight, preferably 8 to 25% by weight, based on the total weight of the polymer resin.

The polymer film of the present invention may be produced by simultaneously mixing and extruding a polyester resin and a styrene resin using a direct extruder and stretching the extruded product in the machine and transverse directions. However, after blending (compounding) polyester resin and styrene resin to obtain a primary resin mixture, the primary resin mixture is melted and extruded to form an amorphous cast sheet, and then the sheet is stretched in the longitudinal and transverse directions. More preferably, the polymer film is produced by forming a film. The term "compounding" is 2
It means that the above solid components are melt-mixed in a predetermined ratio to obtain a homogeneous mixture.

[0026]

The following examples are intended to more specifically illustrate the present invention without limiting the scope of the invention.

The terms and abbreviations used in the specification and examples have their ordinary meanings unless otherwise indicated, eg, "wt%" is weight percent, "° C" is degrees Celsius, and "g.""" Is gram and "dl" is deciliter.

In Examples and Comparative Examples, the properties of polymer films were evaluated according to the following methods.

1. Bulk Density The bulk density of the film was measured by the flotation method using a density gradient tube consisting of carbon tetrachloride and n-heptane at 25 ° C.

2. Antistatic Property The surface resistance of the film was measured at 20 ° C. and 65% relative humidity using an insulation resistance measuring instrument manufactured by Hewlett-Packard Company, USA. The applied voltage was 500V. The measured values are shown in ohms (Ω). The lower the surface resistance of the film, the higher its antistatic properties.

3. Breaking strength The breaking strength of the film is measured by Instron
n) UTM4206 was used to determine the tensile strength according to ASTM D882.

4. Workability The frequency of breakage during the film manufacturing process was measured and workability was classified according to the following criteria.

A: less than once a day.

B: 1-3 times a day.

C: more than 3 times a day.

5. Dimensional stability The dimensional stability of the film was measured by the extent of change in length after 30 minutes at 150 ° C.

Example 1 Dimethyl terephthalate and ethylene glycol were mixed at an equivalent ratio of 1: 2, and transesterification was carried out in the presence of a transesterification catalyst to produce bis-2-hydroxyethyl terephthalate. To this, 16 g of cubic titanium dioxide having an average particle size of 0.5 μm, 0.64 g of potassium octylbenzenesulfonate and a conventional polycondensation catalyst were added, and the mixture was polycondensed to give a glass at 65 ° C. A polyester resin having a transition temperature and an intrinsic viscosity of 0.610 dl / g was produced. Using an ordinary compounder, while maintaining the inlet temperature at 245 ° C., the outlet temperature at 260 ° C., and the discharge temperature at 275 ° C., the obtained polyester resin was converted into polystyrene resin having a melt flow index of 8.0 g / min. The mixture was mixed at a ratio of 1 (w / w) to obtain a primary resin mixture.

The obtained primary resin mixture was extruded through a T-die and rapidly cooled on a cooling drum to obtain a cast sheet. This cast sheet is 3.5 ° C at 95 ° C.
After being stretched at a ratio of 2 times, it was stretched at a rate of 3.8 times in the transverse direction at 110 ° C. to obtain a biaxially stretched polymer film. This biaxially stretched film was heat-treated at 200 ° C. for 5 seconds.

As can be seen from Table 2, the films produced exhibited excellent properties.

Example 2 The procedure of Example 1 was repeated except that the amounts of additives and polystyrene resin and the heat treatment conditions were changed as shown in Table 1.

As can be seen from Table 2, the films produced exhibited excellent properties.

Comparative Example 1-9 The procedure of Example 1 was repeated except that the amounts of additives and polystyrene resin and the heat treatment conditions were changed as shown in Table 1.

As can be seen from Table 2, the films produced exhibited poor properties.

[0044]

[Table 1]

[Table 2] As can be seen from the above results, the polymer film produced by the method of the present invention has excellent antistatic properties, printability, thermal stability and good processability.

Although the present invention has been described in relation to particular embodiments, those skilled in the art can make various modifications and alterations to the present invention, which are also defined in the claims. It should be recognized that it is within the scope of the present invention.

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Claims (6)

[Claims] 1. A styrene resin containing 60% by weight or more of a styrene monomer unit based on the weight of the styrene resin, and a polyester resin containing a sulfonic acid metal salt having an acid value of 1.0 mgKOH / g or less. A step of producing a polymer resin sheet containing; (ii) a step of longitudinally stretching the obtained polymer resin sheet; (iii)
In the method for producing a polymer film, which comprises a step of transversely stretching a longitudinally stretched polymer resin sheet; and (iv) a step of heat-treating the obtained biaxially stretched film, wherein the steps (iii) and (iv) Is carried out under conditions satisfying the following formula: Tg + 20 <Ts <Tg + 60 (1) 80 <Th-Ts <110 (2) 4 <(Th-Ts) / t <30 (3) In the formula, Tg is the glass transition temperature (° C) of the polyester resin; Ts
Is the temperature (° C.) at which the transverse stretching step is performed; Th is the heat treatment temperature (° C.); t is the heat treatment time (seconds). 2. The method for producing a polymer film according to claim 1, wherein the sulfonic acid metal salt is represented by the following formula (4). R ₁ —SO ₃ Me (4) In the formula, R ₁ is a C _{5 to} C ₂₀ alkyl group, and Me is L.
i, Na, K or Mg. 3. The method for producing a polymer film according to claim 1, wherein the sulfonic acid metal salt is added in an amount in the range of 0.01 to 1.0% by weight based on the weight of the polyester resin. . 4. The method for producing a polymer film according to claim 1, wherein the styrene resin is selected from the group consisting of polystyrene, a styrene-butadiene copolymer, a styrene-acrylonitrile copolymer and a mixture thereof. . 5. The method for producing a polymer film according to claim 1, wherein the styrene resin has a melt flow index in the range of 1.0 to 25 g / 10 minutes. 6. The method for producing a polymer film according to claim 1, wherein the styrene resin is added in an amount in the range of 5 to 35% by weight based on the total weight of the polymer resin.