JPH0748465A - Cavity-containing syndiotactic polystyrenic film - Google Patents

Abstract

PURPOSE:To obtain the film, containing many cavities in the interior formed by orienting thereof, faborable in adhesion of an offset ink or a toner, excellent in penciling properties and useful as a poster, etc. CONSTITUTION:This film contains many cavities in the interior formed by at least uniaxially orienting thereof and has <=50% light transmittance. Furthermore, the film is preferably obtained by forming a layer composed of a thermoplastic resin on at least one surface of a layer composed of syndiotactic polystyrene containing the many cavities in the interior thereof and has <=2% heat shrinkage factor and 0.05-1.0mum center line average height. Many inorganic particles are preferably contained in the interior and the periphery thereof is preferably covered with the thermoplastic resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film which, when used on recording paper or the like, has good adhesion of offset ink and toner and excellent pencil drawing property.

[0002]

2. Description of the Related Art Synthetic paper, which is a paper substitute mainly made of synthetic resin, has a higher water resistance, a higher dimensional stability in moisture absorption, and a higher dimensional stability than natural paper.
It has excellent surface stability, gloss and clarity of printing, and mechanical strength. In recent years, application development has been promoted by making use of these advantages. Polyethylene, polypropylene, polyester, and the like are used as main raw materials for synthetic paper, and their applications are being developed by making use of their characteristics.
As a method of obtaining a white film, a method of adding an inorganic pigment such as titanium dioxide or calcium carbonate inside the film is known. In addition, as a method of obtaining a film having a function similar to that of paper mainly made of polyester or polypropylene, (1) a method of containing a large amount of fine voids inside the film or an ordinary flat film (2- It discloses a method of roughening by 1) sand plast treatment, (2-2) chemical etching treatment, (2-3) matting treatment (method of laminating a matting agent with a binder), and the like. However, synthetic paper mainly made of polyester or polypropylene does not have good adhesiveness with toner or ink mainly made of styrene resin. Therefore, a coating layer is provided on the surface,
Adhesion is improved by performing surface treatments such as corona treatment and flame treatment. However, it has been difficult to solve such problems that the cost increases, the heat resistance decreases, and the performance deteriorates with the passage of time by performing such treatment. For that purpose, a white film or sheet made of polystyrene resin as a main material is preferable. However, simply adding an inorganic pigment or the like to whiten a polystyrene film or sheet makes it very brittle, and thus it was not practically usable.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a film excellent in pencil drawability by improving the adhesion of inks and toners used in offset printing, gravure printing, etc. in the previous term.

[0004]

That is, the gist of the present invention as a means for solving these is that the light transmittance, which contains a large number of cavities inside by being oriented in at least one axis, is 50% or less. And a syndiotactic polystyrene film.

Examples of the resin as the main raw material in the present invention include syndiotactic polystyrene. Polystyrene having a syndiotactic structure means that the stereoregularity is a syndiotactic structure, that is, a phenyl group or a substituted phenyl group, which is a side chain with respect to a main chain formed of carbon-carbon bonds, alternates in opposite directions. It has a three-dimensional structure. The styrene polymer in the present invention is not particularly limited in molecular weight, but a weight average molecular weight of 10,000 or more and 3,000,000 or less is desirable (JP-A-3-12).
4427).

The film used in the present invention must have a light transmittance of 50% or less, preferably 30% or less, more preferably 20% or less. The method therefor is not particularly limited. For example, there are a method of applying paint on the surface, a method of applying paper or a non-woven fabric, and the like. However, a method of containing inorganic particles inside or a method of containing a large number of cavities inside is preferable. In the present invention, the inorganic particles contained inside are not particularly limited, and include titanium dioxide, calcium carbonate, barium sulfate, zinc oxide, silicon dioxide, magnesium carbonate, strontium carbonate, aluminum oxide, talc, kaolin, zeolite and these. One kind or two or more kinds of the secondary aggregates can be used. However, in general, these inorganic particles have high surface energy and have a critical surface tension of 50.
It is more than dyne / cm. On the other hand, since the polystyrene resin has a thickness of about 33 dyne / cm, the film or sheet becomes brittle due to the poor interface affinity between the two. Therefore, what is particularly important in the present invention is to improve the affinity and flexibility of these interfaces. A method for improving the affinity is to lower the surface energy, for example, by subjecting the inorganic particles to a surface treatment. A particularly effective method is a method in which the inorganic particles are once pre-kneaded with another resin and then the syndiotactic polystyrene resin is mixed. The resin for that purpose is not particularly limited as long as it has a surface energy larger than that of syndiotactic polystyrene and smaller than that of the inorganic particles, that is, has a critical surface tension of 34 dyne / cm or more and 50 dyne / cm or less. Examples thereof include polyester resins such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyacrylic resins, polysulfone resins, polyamide resins, and polycarbonate resins.

Inner In the present invention, a large number of cavities must be contained inside. The thermoplastic resin which is incompatible with the base resin used in the present invention must be incompatible with the above-mentioned base resin. For example, when syndiotactic polystyrene is the base material, polyester resin, polyacrylic resin, polycarbonate resin, polysulfone resin, cellulose resin and the like can be mentioned. Of these, polymethylpentene and polypropylene are particularly preferable. The polymer mixture obtained by mixing the polyester of the present invention and the incompatible thermoplastic resin to the polyester is obtained, for example, by mixing chips of each resin, melt-kneading in an extruder, and then extruding and solidifying. Method, a method in which both resins are previously kneaded by a kneader, and further melt-extruded by an extruder to solidify, or an incompatible thermoplastic resin is added to the polyester in the polyester polymerization step, and the mixture is stirred and dispersed. It can also be obtained by a method in which chips are melt-extruded and solidified. The polymer obtained by solidifying (unstretched sheet) is usually in a non-oriented state or a weakly oriented state. Also,
The thermoplastic resin which is incompatible with the polyester exists in the polyester in the form of being dispersed in various shapes such as a spherical shape, an elliptic spherical shape, or a thread shape.

Further, since the film in the present invention has a distribution in the inner cavities, the dispersion state of the particles of the thermoplastic resin has a distribution in the thickness direction, and the particle diameter in the vicinity of the surface layer is smaller than that of the central layer. It does not matter whether the particle size is smaller than the particle size or the entire distribution is substantially uniform. The sheet of the polymer mixture of the base resin containing particles of the thermoplastic resin in which the dispersed state has a distribution in the thickness direction has a viscoelasticity and an extrusion condition when the base resin and the thermoplastic resin are melted. Obtained by choosing. For example, by increasing the shear stress acting in the slit of the extrusion die higher than usual, usually a uniform dispersion state of the thermoplastic resin in the thickness direction, particles near the surface layer of a flatter particle size than the normal thermoplastic resin It is possible to obtain a sheet of polymer mixture such that Those having a uniform distribution can be obtained by making the shear stress normal or lower. It is possible to add a colorant, a light-proofing agent, a fluorescent agent, an antistatic agent, etc. to the polymer mixture depending on the application. The polymer mixture thus obtained is further stretched between rolls having different speeds (roll stretch), stretched by gripping and expanding with a clip (tenter stretch), and stretched by expanding by air pressure (inflation stretch). At least one axis is subjected to orientation treatment by, for example, At this time, peeling occurs at the interface between the insoluble thermoplastic resin and the polyester dispersed in the polyester, and a large number of voids are generated in the polymer mixture.

In the present invention, the void content must be 5% by volume or more and less than 50% by volume, preferably 10% by volume or more and less than 30% by volume. If it is less than 5% by volume, the writability with a pencil will be poor. On the other hand, when the content is 50% by volume or more, the film has a low initial elastic modulus and a weak rigidity. Therefore, in the case of a void-containing film, the amount of the thermoplastic resin which is incompatible with the syndiotactic polystyrene mixed with the syndiotactic polystyrene, or the amount of the inorganic particles varies depending on the amount of the intended voids, but the polymer It is preferably 5% by weight to 50% by weight, particularly preferably 8 to 35% by weight, based on the whole mixture. If it is less than 3% by weight, there is a limit to increase the amount of cavities generated, and the desired flexibility, lightness, and drawability cannot be obtained. On the other hand, if it is 40% by weight or more, the heat resistance and strength of the syndiotactic polystyrene film, particularly the strength of the waist, are significantly impaired.

Further, a coating layer can be provided on the surface of the film within the range in which the adhesion of the ink or toner used in the offset printing or gravure printing which is the object of the present invention is not deteriorated. As a method for providing the coating layer, a commonly used method such as a gravure coating method, a kiss coating method, a dip method, a spray coating method, a curtain coating method, an air knife coating method, a blade coating method or a reverse roll coating method can be applied. As the step of applying, a method of previously applying to the surface of the mixed polymer before the orientation treatment, a method of applying to the surface of the uniaxially oriented cavity-containing film and further orienting it in the orthogonal direction, Any method such as coating on the surface of the finished void-containing film is possible.

In the present invention, a so-called composite film in which at least one surface of a basic layer is laminated with another layer may be used. The method is not particularly limited. For example, a method of laminating a molten thermoplastic resin on at least one surface of a biaxially stretched syndiotactic polystyrene film, a method of laminating a molten thermoplastic resin on at least one surface of a uniaxially stretched film. There is no particular limitation, such as a method of laminating and further stretching the laminated body in a direction perpendicular to the laminate, a method of laminating an already stretched film with an adhesive or a pressure-sensitive adhesive. However, from the viewpoint of productivity, it is most preferable to use a so-called co-extrusion method in which the raw materials for the surface layer and the central layer are extruded from different extruders, introduced into one die to obtain an unstretched sheet, and then oriented at least uniaxially. . In this case, inorganic particles, antistatic agent, ultraviolet absorber,
By containing different additives such as a fluorescent whitening agent and an antioxidant in the surface layer and the central layer, it becomes easy to obtain a film satisfying the required properties. For example, in order to achieve both slipping property and hiding property (opacity), particles having a particle size larger than that of the central layer may be added to the surface layer, and an ultraviolet ray inhibitor or a surface protection agent may be added to the surface layer in order to achieve both the ultraviolet protection effect and the hiding property. Examples thereof include surface-treated rutile titanium dioxide, and the central layer containing titanium dioxide, calcium carbonate, or the like.

In the present invention, the unstretched sheet is preferably stretched at least uniaxially. The method may be stretching between rolls having different speeds (roll stretching), stretching by gripping a clip and expanding (tenter stretching), or stretching by expanding by air pressure (inflation stretching). However, from the viewpoint of mechanical properties and the like, sequential biaxial stretching is preferred in which the film is first stretched in the machine direction, which corresponds to the flow direction of the film, and then stretched in the transverse direction. The sequential biaxial stretching in which the machine direction and the transverse direction are sequentially stretched will be specifically described. However, the method is not limited to the following methods as long as the characteristics of the film to be described later are satisfied.

First, the longitudinal stretching is performed by roll stretching. At this time, the draw ratio is 1.2 to 6.0, and the draw temperature is 95 to 1.
It is desirable to carry out in the range of 40 ° C. If the draw ratio is less than 1.2 times, not only the cavities are not sufficiently developed, but also the mechanical strength is insufficient, and if it exceeds 6.0 times, lateral stretching afterwards becomes difficult and a film cannot be obtained. . If the stretching temperature is less than 95 ° C, the sheet will not be softened and stretching will be difficult, and if it exceeds 140 ° C, the crystallinity will be too high and lateral stretching afterwards will be difficult. The heating method of the sheet at the time of stretching may be a heated roll, infrared heating, or any other method. Further, a guide roll or a nip roll may be used at any place of the preheating and stretching rolls. In the subsequent transverse stretching, tenter stretching is desirable. At this time, the draw ratio is 1.2 to 6.0 times, and the draw temperature is 100 to 14
It is desirable to carry out in the range of 0 ° C. Draw ratio is 1.2
If it is less than twice, the mechanical strength will be insufficient, and if it exceeds 6.0 times, fracture tends to occur. If the stretching temperature is less than 100 ° C, the sheet is not softened and it is difficult to stretch the sheet.
If it exceeds, the crystallinity becomes too high and breakage easily occurs. Further, in the present invention, preferably 1 after the stretching is completed.
Heat treatment is performed at 70 to 270 ° C, preferably 200 to 270 ° C. At this time, heat treatment is performed while relaxing 2% or more in the longitudinal direction and / or the transverse direction to obtain a material having a smaller heat shrinkage rate. This heat shrinkage rate is preferably 15
It is to be 2% or less at 0 ° C., more preferably 1.5% or less, and further preferably 1% or less.

The film of the present invention has an initial elastic modulus of 250 kg / mm ² or more and a tensile strength of 10 kg / m in consideration of workability.
m ² or more is preferable. If the initial elastic modulus is less than 250 kg / mm ² and the tensile strength is less than 10 kg / mm ² , troubles during post-processing such as printing are likely to occur. The center line average roughness of the film of the present invention is 0.05 μm or more and 1.0 μm or less, preferably 0.
It must be 1 μm or more and 0.5 μm or less. 0.0
If it is less than 5, the pencil drawability will be poor, and if it exceeds 1.0 μm, the appearance of printed matter will be poor. The white film thus obtained has better adhesion to inks and toners used in offset printing or gravure printing than conventionally proposed white films, so it is a suitable base material for printed matter and information recording paper. Can be provided. In addition to these, labels, posters, cards, recording paper, packaging materials, inkjet paper, video printer image receiving paper, bar code labels, bar code printer image receiving paper, thermal recording paper, maps,
It can be used for dust-free paper, display board, photographic paper, decorative paper, wallpaper, release paper, calendar, magnetic card, tracing paper, pressure-sensitive recording paper, copying paper, clinical examination paper, etc.

[0015]

In the present invention, a thermoplastic resin, preferably syndiotactic polystyrene, is mixed with an incompatible thermoplastic resin to obtain a polymer mixture by mixing the syndiotactic polystyrene with the syndiotactic polystyrene. This is because fine particles of an incompatible thermoplastic resin are dispersed in tactic polystyrene to form a nucleus of a cavity generated by the next alignment treatment. In the present invention, the reason why the polymer mixture is oriented at least uniaxially is to provide appropriate strength, and more preferably to generate a large number of fine voids in the polymer mixture. By forming cavities, the film can be made lighter in weight, workability is improved, and price per area is reduced. In addition, the inclusion of voids increases flexibility and enables clear printing when printing or transferring. Further, by containing voids, hiding power and whiteness can be obtained. Further, a large number of protrusions derived from the thermoplastic resin which is incompatible with the polyester are formed on the surface of the film, which enables writing with a pencil or a ballpoint pen.

Next, examples and comparative examples of the present invention will be shown.
The measurement / evaluation methods used in the present invention are shown below. 1) Density The film was cut into a square of 5.00 cm × 5.00 cm, and its thickness was measured at 50 points, and the average thickness was t μm.
The weight was calculated up to 0.1 mg to be wg, and the weight was calculated by the following formula.

[0017]

[Equation 1]

2) Average porosity of film Calculated by the following formula.

[0019]

[Equation 2] However,

[0020]

[Equation 3]

[0021]

[Equation 4] In the above equation, xi represents the weight fraction of the i component, and di represents the true specific gravity of the i component. The true specific gravity values used in the calculations in the examples were syndiotactic polystyrene 1.05, polymethylpentene 0.83, and anatase type titanium dioxide 3.9 polyethylene terephthalate 1.4.

3) Center line average roughness Measured according to JIS-B601-1982.

4) Initial elastic modulus It was measured according to ASTM D-882-81 (method A).

5) Tensile strength Measured according to JIS-C2318-1975.

6) Heat Shrinkage The film is 200 mm in width 10 mm and length 250 mm
Mark at m intervals and fix under a constant tension of 5 g, and mark intervals A
Measure Subsequently, the mark spacing B after being placed in an oven in an atmosphere of 150 ° C. for 30 minutes under no tension was determined, and the heat shrinkage rate was calculated by the following formula. (A-B) / A x 100

7) Light transmittance According to JIS-K6714, the Poick integrating sphere type H. T.
The light transmittance of the film was measured using an R meter (manufactured by Nippon Seimitsu Optical Co., Ltd.). The smaller this value is, the higher the hiding property is.

8) Surface peel strength Using cellophane tape (18 mm width, made by Nichiban), the surface peel strength was evaluated by a cellophane tape peel test. The peeling angle was in the direction of about 150 degrees while keeping the void-containing film flat. The area of the peeled void-containing film was differentiated as follows. Class 5 ... Peeled off entirely Class 4 ... Almost peeled off Class 3 ... Around half peeled off Class 2 ... Almost peeled off Class 1 ... No peeled off at all

9) Copy Suitability A PPC copying machine was used for copying, and a good appearance was evaluated as ◯,
The bad ones were marked with x.

10) Drawability Whether or not handwriting drawing was possible on the surface of the film was judged with a pencil of HB.

Example 1 Polyethylene terephthalate resin 5 having an intrinsic viscosity of 0.62
Masterbatch pellets (MB) were prepared by pre-kneading 0% by weight and 50% by weight of anatase type titanium dioxide at 285 ° C. using a twin screw extruder. This MB10
% By weight was mixed with 80% by weight of syndiotactic polystyrene resin having a weight average molecular weight of 430,000 and 10% by weight of polymethylpentene resin (RT-18 manufactured by Mitsui Petrochemical Co., Ltd.) and charged into a twin-screw extruder. It was melted at 310 ° C. and extruded from a T-die and electrostatically adhered to a cooling roll to obtain an unstretched sheet having a thickness of about 1000 μm.
This sheet was roll-stretched 3.3 times in the machine direction at 110 ° C., and then stretched 3.5-fold in the transverse direction at 120 ° C.
Finally set to 1 by heat setting while relaxing 4% at ℃
A 00 μm void-containing syndiotactic polystyrene film was obtained.

Comparative Example 1 50% by weight of syndiotactic polystyrene resin having a weight average molecular weight of 430,000 and 50% by weight of anatase type titanium dioxide were pre-kneaded at 310 ° C. using a twin-screw extruder to prepare master batch pellets (MB). It was created. 10% by weight of this MB was added to 80% by weight of a syndiotactic polystyrene resin having a weight average molecular weight of 430,000, and a polymethylpentene resin (RT-18 manufactured by Mitsui Petrochemical Co., Ltd.) 10
3% by weight, put into a twin screw extruder,
It was melted at 10 ° C. and extruded from a T-die and electrostatically adhered to a cooling roll to obtain an unstretched sheet having a thickness of about 1000 μm. Then, in the same manner as in Example 1, a white syndiotactic polystyrene film having a final thickness of 100 μm was obtained.

Comparative Example 2 Masterbatch pellets (MB) were prepared by pre-kneading 50% by weight of syndiotactic polystyrene resin having a weight average molecular weight of 430,000 and 50% by weight of anatase type titanium dioxide at 310 ° C. using a twin screw extruder. It was created. 10% by weight of this MB was mixed with 90% by weight of syndiotactic polystyrene resin having a weight average molecular weight of 430,000, charged into a twin-screw extruder and melted at 310 ° C.
An unstretched sheet having a thickness of about 1000 μm was obtained by extruding from a die and electrostatically adhering to a cooling roll. Then, in the same manner as in Example 1, a white syndiotactic polystyrene film having a final thickness of 100 μm was obtained.

Comparative Example 3 Intrinsic viscosity 0.62 polyethylene terephthalate resin 50
% By weight and 50% by weight of anatase type titanium dioxide were pre-kneaded at 285 ° C. using a twin-screw extruder to prepare masterbatch pellets (MB). 10% by weight of this MB was mixed with 80% by weight of polyethylene terephthalate resin having an intrinsic viscosity of 0.62 and 10% by weight of polymethylpentene, charged into a twin-screw extruder, melted at 290 ° C., and extruded from a T-die. By electrostatically adhering to, an unstretched sheet having a thickness of about 1000 μm was obtained. Then, in the same manner as in Example 1, a final thickness of 100
A polyester film containing voids of μm was obtained.

Example 2 10% by weight of each MB prepared in Example 1, 80% by weight of syndiotactic polystyrene resin having an average weight molecular weight of 430,000, and polymethylpentene resin (RT-18 manufactured by Mitsui Petrochemical Co., Ltd.) ) 10% by weight as the raw material for the A layer, 10% by weight for each MB, 90% by weight for the syndiotactic polystyrene resin as the raw material for the B layer, and melted at 310 ° C. in different twin screw extruders, respectively. Of the unstretched sheet obtained by laminating the melted product of No. 1 through a T-die and electrostatically adhering the melted product onto a cooling roll at 110 ° C.
Roll-stretched 3.3 times at 120 ° C., then horizontally stretched 3.5 times at 120 ° C. with a tenter, heat-set at 250 ° C. with 4% relaxation, and have a cavity of B / A / B = 15/120/15 μm. A composite white syndiotactic polystyrene film containing was obtained.

[0035]

EFFECTS OF THE INVENTION The void-containing syndiotactic polystyrene film of the present invention has better adhesiveness to inks and toners used in offset printing and gravure printing than conventional white films, and therefore labels, posters, printing papers, Especially excellent for offset printing, gravure printing, commercial printing, thermal recording paper, sublimation transfer recording paper, printing base materials for printers, etc., and also excellent for delivery slips, electronic white boards, pressure sensitive paper, PS boards, printing boards, packaging materials, etc. It is a base material.

[0036]

[Table 1]

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Claims (4)

[Claims] 1. A void-containing syndiotactic polystyrene-based film having a light transmittance of 50% or less, which has a large number of voids inside by orienting at least uniaxially. 2. A void-containing syndiotactic layer comprising a layer (B) made of a thermoplastic resin provided on at least one surface of a layer (A) made of syndiotactic polystyrene having a large number of voids inside. Polystyrene film. 3. The film according to claim 1 or 2, wherein the heat shrinkage is 2% or less, and the center line average roughness is 0.05 μm or more and 1.0 μm or less. Cavity-containing syndiotactic polystyrene film. 4. The film according to claim 1, wherein the film contains a large number of inorganic particles, and the periphery of the inorganic particles is covered with a thermoplastic resin. Syndiotactic polystyrene film.