JPH06322154A - White film - Google Patents

Abstract

PURPOSE:To obtain a film being bright in printing and copying, having high opacifying property even in the case of thin film and especially suitable for printing, heat-sensitive recording, printing paper by optimizing the distribution of hollow. CONSTITUTION:The while film has >=10mum and <=30mum thickness and <=30% light permeation and <=40% gloss of film surface and >=75 whiteness and substantially contains no inorganic particles having >=2mum diameter in the interior.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white film which is thin and has good hiding power, drawing property, film strength and productivity.

[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.

As a method of obtaining a film having a function similar to that of paper mainly made of polyester, polypropylene, polyethylene, etc., a method of containing a large amount of fine voids inside the film can reduce the weight of the film itself. There is an advantage that appropriate flexibility can be given and clear printing and transfer are possible.

As a method for forming fine voids inside the film, for example, a polymer incompatible with polyester is melt-kneaded by an extruder to obtain a sheet in which the polymer is dispersed in fine particles to obtain a sheet. A method has been proposed in which cavities are formed around fine particles by stretching.

However, the conventional white films have a problem that the properties such as hiding property and film strength and the film forming property are deteriorated as the white film becomes thinner. For example, Japanese Patent Publication No. 54-29550 discloses a film having a thickness of 22 μm and a scattered light transmittance of 18%. However, these have concealing properties and whiteness due to the scattering of the cavities that are substantially developed inside, but since they do not contain inorganic particles or are not suitable for inclusion, they lack whiteness and are of high gloss. It was a poor feeling. Further, voids and inorganic particles having a large particle size are present on the surface, which causes printing omission.
Further, for example, JP-A-63-200147 discloses a method of adding a large number of inorganic particles to the surface layer. However, in this method, since the ratio of the thickness of the surface layer to the thickness of the entire surface layer is too large, a film having a thickness of about 100 μm can be formed, but when it becomes 30 μm, it becomes very difficult.

[0006]

DISCLOSURE OF THE INVENTION The present invention is intended to provide a film which is free from the above-mentioned drawbacks and is excellent in concealing property, film strength, glossiness and film-forming property even if it is thin.

[0007]

Means for Solving the Problems That is, the present invention has a thickness of 10 μm or more and 30 μm or less, a light transmittance of 30% or less, a film surface gloss of 40 or less, and a whiteness of 75 or more,
In addition, the present invention relates to a white poly film characterized in that substantially no inorganic particles of 2 μm or more are present inside.

In the present invention, if the thickness, light transmittance and the like satisfy the above-mentioned conditions, a single-layer film composed of one thermoplastic resin layer may be used, or at least one side of the base layer (A) may have the same or different heat resistance. A composite film composed of the plastic resin layer (B) may be used.

In the present invention, the base resin is a polyolefin resin, a polyamide resin, a polyacrylic resin,
Polystyrene resin, polysulfone resin, polyether resin, etc. are not particularly limited. However, a polyester resin as described below is preferable.

The polyester in the present invention means an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid or naphthalenedicarboxylic acid or an ester thereof and a glycol such as ethylene glycol, diethylene glycol, 1,4-butanediol or neopentyl glycol. It is a polyester produced by condensation. These polyesters may be obtained by directly reacting an aromatic dicarboxylic acid with a glycol, and then transesterifying an alkyl ester of an aromatic dicarboxylic acid with a glycol, followed by polycondensation, or a diglycol ester of an aromatic dicarboxylic acid. Is produced by a method such as polycondensation. Typical examples of such polyesters include polyethylene terephthalate, polyethylene butylene terephthalate and polyethylene-2,6-naphthalate. This polyester may be a homopolymer or a copolymer of a third component. In any case, in the present invention, the resin for the layer A has an ethylene terephthalate unit, a butylene terephthalate unit or an ethylene-2,6-naphthalate unit of 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more. Is preferred. The resin for the layer B may be such a homopolymer, a copolyester, or a mixture of a homopolymer and a copolyester.

In the present invention, in order to impart drawing properties, cushioning properties and concealing properties, a single layer film or a layer A of the composite film is preferably a void-containing film having a large number of voids inside. . As the method, for example, a method has been proposed in which a large number of cavities are contained inside by melting and extruding a thermoplastic resin containing a foaming agent and an inert gas such as nitrogen. Although any method may be used in the present invention, it is preferably a method in which a large number of incompatible thermoplastic resins are contained in polyester and a large number of cavities are contained inside by stretching at least uniaxially.

Specific examples of the thermoplastic resin which is incompatible with polyester used in the present invention include polystyrene resin, polyolefin resin, polyacrylic resin, polycarbonate resin, polysulfone resin, cellulose resin and the like. To be In particular, polystyrene resins, polyolefin resins such as polymethylpentene and polypropylene are preferable.

The polymer mixture of the present invention in which the incompatible thermoplastic resin is mixed with the polyester and the polyester is prepared, for example, by mixing chips of each resin, melt-kneading in an extruder, and then extruding and solidifying. Method, or a method in which both resins are kneaded in advance 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 dispersed by stirring. It can also be obtained by a method of melt-extruding and solidifying the obtained chips. The polymer obtained by solidifying (unstretched sheet) is usually in a non-oriented state or a weakly oriented state. Further, the thermoplastic resin incompatible with the polyester is present in the polyester in a shape dispersed in various shapes such as a spherical shape, an elliptic spherical shape, or a thread shape.

A particularly important point in the present invention is a method of containing inorganic particles. Usually, as a means for imparting concealing property to a plastic film, that is, a means for lowering the light transmittance, a method of expressing a large number of internal cavities, applying a pigment or a dye to the surface layer of the film, or containing a large number of inorganic particles inside is used. There is. However, if the content of cavities or inorganic particles is further increased in order to further improve the hiding property, there arises a problem that the strength of the film decreases and the film-forming property becomes unstable. Further, when the coating amount of the pigment is increased, there is a problem that the pigment comes off. Therefore, as a method for improving the hiding property so that these problems do not occur, inorganic particles are concentrated and added at a specific place inside the film.

In the case of an ordinary void-containing polyester film, the added inorganic particles such as titanium dioxide, calcium carbonate, silicon dioxide and barium sulfate are all uniformly present in the matrix polyester. Therefore, when the addition amount of the inorganic particles is increased, the interface generated between the polyester and the inorganic particles is increased, and the tensile strength and film formability of the film are likely to decrease. This is a problem that is particularly noticeable in a film having a thickness of 30 μm or less.

Therefore, as one of means for solving these problems, there has been proposed a method of treating the surface of inorganic particles with an inorganic substance containing aluminum, silicon, zinc or the like to increase the affinity with polyester. However, with these methods, it is difficult to contain a large amount of inorganic particles so as to achieve a light transmittance of 30% or less at a thickness of 30 μm or less, and to maintain film strength and film formability. This is because the inorganic particles have a high surface energy and thus have a higher affinity for the polyester having a higher surface energy than the cavity developing agent.

Therefore, as one of the means to reach the present invention,
To increase the amount of addition of inorganic particles to improve the hiding property, not to uniformly disperse all the inorganic particles in the polyester, around the cavities and the cavity-developing agent, preferably a method of allowing it to exist in the cavity-developing agent, etc. Can be given. In the present invention, in particular, a method of adding 20 to 70% by weight, preferably 30 to 50% by weight of inorganic particles to the layer B is preferable in order to have hiding properties and whiteness and to reduce surface gloss. Especially B
By concentrating the addition to the layer, the hiding property and the whiteness can be more effectively exhibited than in the case where the addition amount is the same evenly. In addition, these inorganic particles have an average particle size of 0.1 μm or more and less than 1 μm and substantially 2
It is preferable not to include particles having a size of μm or more. If the average particle size is less than 0.1 μm, sufficient hiding property, low gloss and whiteness cannot be provided. When the average particle size is 1 μm or more, or when the particles include particles of 2 μm or more, printing defects may occur due to the large particles when printing with a printer or the like. When concentratedly added to the B layer, stretching may be difficult or uneven thickness of the B layer may occur depending on the particle size and the amount of the inorganic particles. In that case B
It is effective to mix the polyester serving as the base material of the layer with a copolymerized polyester or polyester resin elastomer having a low glass transition temperature or crystallinity. In the present invention, the inorganic particles include, but are not particularly limited to, titanium dioxide, silicon dioxide, calcium carbonate, barium sulfate, aluminum oxide, kaolin, talc and the like, but titanium dioxide is preferable from the viewpoint of hiding property. is there. However, the thickness is 10 μm or more and 30 μm or less, the light transmittance is 30% or less, the gloss is 40% or less, and the whiteness is 75%.
The above is not particularly limited.

An important point in the present invention is that any B
The thickness of the layer is 0.4 μm or more and 3 μm or less, and A of the B layer is
The thickness ratio to the layer is preferably B / A = 0.15 or less. If it is less than 0.4 μm, it is difficult to make the hiding property, low gloss and whiteness within the intended ranges. Also 3μ
When m or more or B / A = 0.15 is exceeded, the stretching stress at the time of stretching becomes too high, which makes stretching difficult. Alternatively, the film strength is significantly reduced. This phenomenon has a thickness of 30
It becomes particularly noticeable in a film having a thickness of μm or less. Therefore 30
This is because it is difficult to apply the film forming technology for a film having a thickness of more than 30 μm to the film forming process for a film having a thickness of 30 μm or less.

A polymer mixture obtained by mixing the polyester and the polyester with an incompatible thermoplastic resin of the present invention is prepared, for example, by mixing chips of each resin, melt-kneading in an extruder, and then extruding and solidifying. Method, or a method in which both resins are kneaded in advance 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 dispersed by stirring. It can also be obtained by a method of melt-extruding and solidifying the obtained chips. 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 resulting polymer mixture 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 (stretching). At least uniaxially oriented by, for example, inflation stretching). By the orientation treatment, peeling occurs at the interface between the polyester and the void-developing agent, and voids are developed.

Therefore, the amount of the thermoplastic resin which is incompatible with the polyester to be mixed with the polyester varies depending on the amount of the target cavities, but is preferably 3% by weight to 40% by weight based on the whole polymer mixture, preferably Is 8% by weight
It is 20% by weight. 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, when it is 40% by weight or more, the heat resistance and strength of the polyester film are significantly impaired.

The conditions for orienting the polymer mixture are closely related to the formation of cavities. Therefore, the conditions for achieving the object of the present invention include, for example, the most commonly used sequential biaxial stretching step, in which a continuous sheet of the polymer mixture is roll-stretched in the longitudinal direction and then in the width direction. In the case of the sequential biaxial stretching method in which the tenter stretching is performed, it is as follows. In roll drawing, it is preferable to set the temperature at 80 to 120 ° C. and the magnification at 1.2 to 5 times in order to generate a large number of cavities. In the tenter stretching, the temperature is preferably 100 to 140 ° C. and the magnification is preferably 1.2 to 5 in order to stably form a film without breaking. It is desirable to carry out the heat treatment condition after stretching by the method described below. After the stretching, the heat treatment must be performed at 200 ° C. or higher, preferably 220 ° C. or higher, more preferably 230 ° C. or higher. Also,
At this time, heat setting must be performed while relaxing by 3 to 8%. Below 200 ° C or below 3%, 150 ° C
A void-containing film having a heat shrinkage of less than 2%, preferably less than 1.7%, more preferably less than 1.5% cannot be obtained.

In the present invention, the average content of voids in the entire layer is preferably 10% by volume or more. When the average porosity of the whole layer is less than 10% by volume, the flexibility peculiar to the void-containing polyester film becomes insufficient, and the drawing property and cushioning property also become insufficient.

The average porosity is 40 vol% or less, preferably 30 vol% or less, and the average porosity is 4 or less.
A void-containing film of 0% by volume or more is difficult to manufacture because it frequently breaks during the stretching process, and the resulting film is not preferable because the surface strength and tensile strength are insufficient. Considering post-processing such as printing, the film of the present invention preferably has a breaking strength of 11 kg / mm ² or more in both length and width.

In the present invention, a single-layer film composed of one layer may be used, but a composite film in which different layers are laminated on at least one side of the A layer serving as a base material is preferable. In this case, the A and B layers may have completely the same raw material composition or different raw material compositions, but preferably the A layer is a layer having a base material of polyester and containing voids, and the B layer is a base material of polyester having an average particle size of less than 1 μm. It is a layer containing inorganic particles. In this case, the A and B layers may be the same or different. The manufacturing method is a method of laminating two or more stretched films or melting the raw material of the layer A,
The method of stretching the extruded unstretched sheet in the uniaxial direction, laminating the unstretched sheet of the layer B, and stretching in the perpendicular direction is not particularly limited. However, in consideration of productivity and the like, the raw materials for the A layer and the B layer are put into separate extruders, melted and extruded, introduced into one die to obtain an unstretched sheet, and then oriented in at least uniaxial manner. Most preferred is lamination by extrusion. The stacking method is A
It may be a so-called multi-manifold type die in which different melts of layers B and B are laminated in a die, or a method in which different melts are laminated in a pipe and extruded from a single manifold type die to obtain an unstretched sheet. .

Further, by providing a coating amount on the film surface, the wettability and the adhesiveness of the ink and the coating agent are improved. The compound constituting the coating layer,
Polyester resins are preferred, but in addition to these, compounds disclosed as means for improving the adhesiveness of ordinary polyester films such as polyurethane resins, polyester urethane resins and acrylic resins can be applied. 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 finished film surface is possible.

The film thus obtained has a thickness of 3
The light transmittance is 30% or less, preferably 25 at 0 μm or less.
% Or less, more preferably 20% or less. If it exceeds 30%, the back side can be seen through, which is not preferable for printed matter. The surface gloss is preferably 40% or less, preferably 30% or less, more preferably 20% or less. If it exceeds 40%, the luster is strong and the high-class feeling is impaired. The whiteness is 75 or more, preferably 80 or more. If it is less than 75, the quality is poor.

The thus-obtained film has good hiding property, is strong and has excellent surface strength and resistance to cleavage even if it is particularly thin. Therefore, when the void-containing polyester film of the present invention is used as a substrate, , Label, poster, card, recording paper, packaging material, video printer image receiving paper, barcode label, barcode printer image receiving paper, thermal recording paper, map, dust-free paper, display board, white board, electronic white board, photographic paper, decorative paper , Wallpaper, banknote, release paper, origami, calendar, magnetic card, tracing paper, slip, delivery slip, pressure-sensitive recording paper, copy paper, clinical test paper, parabolic antenna reflector, etc.

[0029]

EXAMPLES Examples of the present invention will be described below. 1) Intrinsic viscosity of polyester Polyester was dissolved in a mixed solvent of phenol (6 parts by weight) and tetrachloroethane (4 parts by weight) and measured at 30 ° C. 2) Melt Flow Index of Polystyrene Resin Measured at 200 ° C. under a load of 5 kg according to JIS-K7210. 3) Density The film is accurately cut into a square of 5.00 cm × 5.00 cm, the thickness is measured at 50 points, and the average thickness is t μm.
The weight was calculated up to 0.1 mg to be wg, and the weight was calculated by the following formula. Apparent specific gravity (−) = w / 5 × 5 × t × 10000 4) Average porosity of film Calculated by the following formula. Cavity content rate (volume%) = 100 × (1-true specific volume / apparent specific volume) However, true specific volume = x ₁ / d ₁ + x ₂ / d ₂ + x ₃ / d ₃ + ... +
x _i / d _i + ... Apparent specific volume = 1 / apparent specific gravity of film In the above formula, xi represents the weight fraction of the i component, and di represents the true specific gravity of the i component. The values of true specific gravity used in the calculations in the examples were polyethylene terephthalate 1.40, general-purpose polystyrene 1.05, polypropylene 0.92, and rutile titanium dioxide 4.2. 5) Light transmittance According to JIS-K6714, Poic 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, the higher the concealing property. 6) Tensile strength of film It was performed based on JIS-C2318. 7) Gloss According to JIS-Z8741-1983, gloss meter V
Using GS-1001DP (manufactured by Nippon Denshoku Industries Co., Ltd.),
The values at an incident angle and a reflection angle of 60 ° were measured. The higher this value, the higher the glossiness. 8) Whiteness The whiteness was measured according to JIS-L1015-1981-B method using Z-1001DP of Nippon Denshoku Industries Co., Ltd. 9) Missing printing Sanyo Electric Co., Ltd. word processor SANWORD
When printed with SWP-360, those having a good appearance were evaluated as ◯, and unnecessary ones were evaluated as x.

Example 1 Polyester resin obtained by copolymerizing 75% by weight of polyethylene terephthalate resin having an intrinsic viscosity of 0.62 as a raw material with dimethyl terephthalate as a dicarboxylic acid component and butanediol and polytetramethylene glycol as a glycol component in a molar ratio of 85:15. 5% by weight of elastomer, 15% by weight of general-purpose polystyrene with a melt flow index of 2.0 g / 10 minutes, 5% by weight of anatase type titanium dioxide having an average particle size of 0.3 μm as the raw material of the A layer, and polyethylene as the raw material of the B layer. 60% by weight of terephthalate resin,
40 wt% of anatase type titanium dioxide was melt extruded from a T-die at 290 ° C. by separate twin screw extruders, electrostatically adhered and solidified on a cooling rotary roll, and each layer had B / A / B = 15. An unstretched sheet of a / 220/15 μm polymer mixture was obtained. Subsequently, the unstretched sheet was longitudinally stretched 3.5 times at 83 ° C. by a roll stretching machine, and then horizontally stretched 3.5 times at 130 ° C. by a tenter and then 23 times.
Heat treatment was carried out at 5 ° C. with 4% relaxation to obtain a polyester film containing a large number of cavities inside. Thickness is B / A
/B=1.5/22/1.5 μm. The void content of the entire obtained film was 20% by volume. Apparent specific gravity is 1.18, light transmittance is 15%, thickness is 25 μm,
The gloss was 28%, the whiteness was 83, and the tensile strengths in the longitudinal and transverse directions of the film were 13 kg / mm ² .

Comparative Examples 1, 2 B / A / B thickness ratios of 5/15/5 and 0.1 / 25 /
A void-containing polyester film was obtained in the same manner as in Example 1 except that the content was 0.1.

Comparative Example 3 A void-containing polyester film was obtained by the same method except that the amount of titanium dioxide in the B layer was changed to 15% by weight.

Comparative Example 4 76% by weight of polyethylene terephthalate resin having an intrinsic viscosity of 0.62 as a raw material and a melt flow index of 2.0
g / 10 minutes Polystyrene 15% by weight, 9% by weight of anatase type titanium dioxide having an average particle size of 0.3 μm
As the raw material of the layer, 91 wt% of polyethylene terephthalate resin and 9% of the anatase type titanium dioxide are used as the raw material of the B layer.
A void-containing polyester film was obtained in the same manner as in Example 1 except that the respective weight% were charged into different twin screw extruders. During film formation, breakage occurred frequently and was not stable. The obtained film had many surface roughness due to cavities. The obtained light transmittance was 20%, the gloss of the film was 70%, the whiteness was 72, and the tensile strength was 8 kg / mm ² in both length and width.

The results of these Examples and Comparative Examples are summarized in Table 1.

[0035]

[Table 1]

[0036]

EFFECT OF THE INVENTION The polyester film of the present invention, like the conventional void-containing polyester film obtained by using polystyrene or polyolefin as a void-developing agent,
It has the advantages of lightness, flexibility, matteness, drawing properties, and the like, and has a high concealing property even if it is thinner than conventional films. Therefore, the polyester film of the present invention can be used in a very wide range of fields such as labels, posters, recording papers, packaging materials, heat-sensitive recording materials and printing papers.

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[Procedure amendment]

[Submission date] June 24, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0005

[Correction method] Change

[Correction content]

However, the conventional white films have a problem that the properties such as hiding property and film strength and the film forming property are deteriorated as the white film becomes thinner. For example, Japanese Patent Publication No. 54-29550 discloses a film having a thickness of 22 μm and a scattered light transmittance of 18%. However, these have concealing properties and whiteness due to the scattering of the cavities that are substantially developed inside, but since they do not contain inorganic particles or are not suitable for inclusion, they lack whiteness and are of high gloss. It was a poor feeling. Further, voids and inorganic particles having a large particle size are present on the surface, which causes printing omission.
Further, for example, JP-A-63-200147 discloses a method of adding a large number of inorganic particles to the surface layer. However, in this method, since the ratio of the thickness of the surface layer to the thickness of the entire surface layer is too large, a film having a thickness of about 100 μm can be formed, but if it is 30 μm or more, it becomes very difficult.

Claims (5)

[Claims] 1. An inorganic particle having a thickness of 10 μm or more and 30 μm or less, a light transmittance of 30% or less, a gloss of a film surface of 40% or less, a whiteness of 75 or more, and 2 μm or more inside thereof. White film characterized by. 2. A white polyester film, characterized in that the film of claim 1 comprises at least two layers in which a polyester layer (A) as a base is provided with a layer (B) made of polyester on at least one surface. . 3. An average particle size of 1 in the polyester layer (B).
The white polyester film according to claim 2, wherein the inorganic particles of less than μm are contained in an amount of 20 to 70% by weight. 4. The optional polyester layer (B) has a thickness of 0.4 μm or more and 3 μm or less, and a ratio of the thickness of each B layer to the thickness of the A layer is 0.15 or less. 2 or 3 white polyester film. 5. The A layer contains a large number of cavities, and the average void content of the entire film is 10% by volume or more and 40% by volume.
The void-containing white polyester film according to any one of claims 2 to 4, wherein: