JP2008255142A - Biaxially stretched polyester film for simultaneous forming and transfering - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially stretched polyester film suitable for a film for simultaneous forming and transfering hardly developing faults such as blocking, etc., in a process of producing the transfer sheet and capable of printing minutely. <P>SOLUTION: This biaxially stretched polyester film used for simultaneous forming and transfering and having a coated layer is characterized by having 1 to 20 nm Ra surface roughness of the coated layer, and also 25 to 100 nm surface roughness of the other surface. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a biaxially stretched polyester film for simultaneous molding and transfer that is useful as a support film for a simultaneously molded decorative sheet used for decorating resin molded products such as electric products and automobile parts.

  As a method for decorating a plastic molded product having a curved surface such as an electric appliance, a so-called in-mold molding method in which transfer printing is performed simultaneously with molding is widely used. The in-mold molding method uses a heat and pressure during plastic injection molding to create a transfer sheet in which a printing layer consisting of a release layer, ink layer, adhesive layer, etc. is laminated on a substrate film in advance. Transfer printing.

  The surface in contact with the release layer of the support film is required to be a smooth surface in order to improve the appearance quality of the molded product. On the other hand, since the transfer sheet is wound up in a roll shape in the printing layer processing step, the surface opposite to the surface that contacts the release layer of the support film is in contact with the adhesive layer that forms the outermost surface of the printing layer. It is important that no print peeling occurs due to the above.

Recently, improvement in production in the transfer sheet production process and improvement in handleability of the film have been demanded, and there is an increasing demand for prevention of blocking between the support film and the adhesive layer.
JP 2006-187951 A

  The present invention has been made in view of the above circumstances, and its solution is to provide a biaxially stretched polyester film for simultaneous transfer molding that is less likely to cause blocking in the transfer sheet production process and capable of fine printing. is there.

  As a result of intensive studies, the present inventors have found that the above problem can be easily solved by using a polyester film having a specific configuration, and have completed the present invention.

  That is, the gist of the present invention is a biaxially stretched polyester film having a coating layer, wherein the coating layer has a surface roughness Ra of 1 to 20 nm and the other surface has a surface roughness of 25 to 100 nm or less. It exists in the biaxially stretched polyester film for simultaneous shaping | molding transcription | transfer characterized by being.

Hereinafter, the present invention will be described in detail.
The polyester in the present invention is an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, ethylene glycol, diethylene glycol, trimethylene glycol, tetramethylene glycol, neopentyl glycol, 1, This polyester is mainly composed of an ester with glycol such as 4-cyclohexanedimethanol. The polyester is obtained by directly polymerizing an aromatic dicarboxylic acid and a glycol, or by a transesterification reaction between an aromatic dicarboxylic acid dialkyl ester and a glycol, followed by polycondensation, or an aromatic dicarboxylic acid diglycol. It can also be obtained by a method such as polycondensation of an ester. Typical examples of the polyester include polyethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate (PEN), polybutylene terephthalate, and the like. Such a polyester may be a homopolymer that is not copolymerized, 40 mol% or less of the dicarboxylic acid component is a dicarboxylic acid component other than the main component, and 40 mol% or less of the diol component is a diol component other than the main component. It may be a certain copolyester or a mixture thereof.

  The film of the present invention is a coextruded laminated film composed of at least two layers. When the A layer is formed as the surface on which the easy-adhesion coating layer is provided and the other layers are the B layer and the C layer, for example, A / B, A / B / A ′ and A / B / C can be employed. A 'represents a layer made of the same polyester raw material as the A layer and having a different layer thickness.

  One surface of the film of the present invention has a coating layer, and the surface roughness Ra of the coating layer surface is in the range of 1 to 20 nm, preferably 15 nm or less, more preferably 10 nm or less. When Ra exceeds 20 nm, the surface roughness may be transferred to the printing layer, and the surface gloss of the molded product may be lost. Further, it is difficult to make the surface roughness Ra less than 1 nm even if fillers such as particles are removed from the polyester raw material constituting the coating layer side.

  The surface roughness Ra of the film of the present invention opposite to the surface of the coating layer is in the range of 25 to 100 nm, and preferably in the range of 30 to 90 nm. When the surface roughness Ra is less than 25 nm, the anti-blocking property is inferior. On the other hand, when the surface roughness Ra exceeds 100 nm, it is difficult to see the pattern or the like of the printed layer, which adversely affects the appearance inspection of the transfer sheet.

  The film of the present invention usually has a coating layer on the surface in contact with the release layer of the printing layer. It is preferable that the coating layer can improve the adhesion between the release layer of the printing layer and the support film. If there is no coating layer, the adhesiveness between the release layer and the support film is insufficient, peeling occurs between the release layer and the support film in the transfer process, and the peeled print layer adheres to the molded product As a result, the appearance quality of the molded product may be deteriorated.

  This coating layer is usually composed mainly of a polymer and a crosslinking agent. The polymer is preferably composed of at least one of water-based polyurethane, water-based polyester and water-based acrylic resin, more preferably has a glass transition temperature (Tg) of 0 ° C. or higher, more preferably 40 ° C. or higher, particularly preferably. Among the polyurethanes, polyester polyurethane is used and has a carboxylic acid residue, and at least a part of the polyurethane is made aqueous using an amine or ammonia. As the crosslinking agent, melamine-based, epoxy-based, or oxazoline-based resins are generally used, but melamine-based resins are preferable from the viewpoints of coating properties and durable adhesiveness.

  Moreover, an antifoamer, a coating property improving agent, a thickener, a disinfectant, inorganic particles, and organic particles can be added to the coating layer as necessary.

  For example, Yuji Harasaki, Tsuji Shoten, published in 1979, “Coating Method”, as shown in “Coating Method”, Reverse Roll Co., Gravure Co., Rod Co. Co., Air A doctor or overnight or other coating device can be used. The coating layer may be formed only on one side of the polyester film or on both sides. When it is formed only on one side, an application layer different from the above-mentioned application layer can be formed on the opposite side as necessary to give other characteristics. In addition, in order to improve the applicability | paintability to the film of a coating agent and adhesiveness, you may perform a chemical process and an electrical discharge process to a film before application | coating. Moreover, in order to further improve the surface characteristics, a discharge treatment may be performed after the coating layer is formed.

  The thickness of the coating layer is usually in the range of 0.01 to 0.5 μm, preferably 0.02 to 0.3 μm, as the final dry thickness. When the thickness of the coating layer is less than 0.01 μm, the adhesiveness becomes inferior, and the effects of the present invention may not be obtained. In that case, the print quality is deteriorated. On the other hand, when the thickness of the coating layer exceeds 0.5 μm, the stability of the coating solution is lowered, and coating unevenness may occur.

  In the present invention, the heat shrinkage rate for 5 minutes at 180 ° C. in the longitudinal and transverse directions of the film is usually 3.0% or less, more preferably 2.5% or less. If the thermal shrinkage rate exceeds 3.0%, printing distortion tends to occur due to film shrinkage at the time of printing on the film or at the time of molding.

The surface specific resistance of the film of the present invention is preferably 1 × 10 ¹³ Ω / □ or less, more preferably 1 × 10 ¹² Ω / □ or less. If the surface specific resistance exceeds 1 × 10 ¹³ Ω / □, charging due to frictional charging occurs, which may cause problems when the support film is peeled off during the transfer sheet production process or molding process.

  To reduce the surface resistivity, there are a method of further providing an antistatic coating layer on the opposite side of the coating layer and a method of adding an antistatic property to the coating layer. In the latter case, it is easy to add an antistatic agent. The former may be adversely affected and the former is preferred.

  For the antistatic coating layer, the coating solution contains a nonionic, anionic, cationic or amphoteric organic compound, a compound commonly referred to as an antistatic agent that absorbs static electricity by absorbing moisture. Specific examples of the antistatic agent include the following.

  Nonionic antistatic agents include polyether compounds or derivatives thereof. Specific examples include polyethylene glycol, polypropylene glycol, polyethylene glycol / polypropylene glycol block copolymers, polyoxyethylene diamine, polyether / polyester / polyamide. Block copolymers fall under this category. Examples of the anionic antistatic agent include compounds having sulfonic acid, carboxylic acid, phosphoric acid, boric acid and salts thereof.

  Of these, sulfonic acid antistatic agents are often used because of their strong antistatic properties and industrial availability. Examples thereof include polystyrene sulfonate, lithium polystyrene sulfonate, sodium polystyrene sulfonate, potassium polystyrene sulfonate, cesium polystyrene sulfonate, and ammonium polystyrene sulfonate.

  Typical examples of the cationic antistatic agent include primary amine hydrochlorides, secondary amine hydrochlorides, tertiary amine hydrochlorides, and quaternary ammonium salts as low molecular weight compounds. Examples of amines used include monomethylamine, dimethylamine, trimethylamine, laurylamine, dilaurylamine, lauryldimethylamine, stearylamine, distearylamine, stearyldimethylamine, monoethanolamine, diethanolamine, triethanolamine, ethylenediamine, diethylenetriamine, N, N-diethylethylenediamine, aminoethylethanolamine, pyridine, morpholine, guanidine, hydrazine and the like can be mentioned.

  Examples of the quaternary ammonium salt include lauryltrimethylammonium chloride, lauryldimethylbenzylammonium chloride, cetylpyridinium chloride, cetylpyridinium bromide, stearamidemethylpyridinium chloride, lauryltrimethylammonium methosulfate and the like. Examples of the polymeric cationic antistatic agent include a quaternary ammonium salt type styrene polymer, a quaternary ammonium salt type aminoalkyl (meth) acrylate polymer, a quaternary ammonium salt type diallylamine polymer, and the like.

  Amphoteric antistatic agents include carboxylate-type amphoteric surfactants with amine salt-type cations, carboxylate-type amphoteric surfactants with quaternary ammonium salt-type cations (so-called betaine-type amphoteric surfactants) Is famous. For example, sodium laurylaminopropionate, lauryl dimethyl betaine, stearyl dimethyl betaine, lauryl dihydroxyethyl betaine, etc. are mentioned.

  Further, the surface resistivity can be lowered by adding an antistatic agent to the film itself. Examples of the antistatic agent that can be added to the film include the following compounds. Cationic compounds such as primary amine salts, tertiary amines, quaternary ammonium compounds, sulfurized oils, sulfated amide oils, sulfated ester oils, fatty alcohol sulfates, alkyl sulfates, fatty acid ethyl sulfones Acid salts, alkyl sulfonates, alkyl naphthalene sulfonates, alkyl benzene sulfonates, phosphate esters, and other anionic compounds, partial fatty acid esters of polyhydric alcohols, ethylene oxide adducts of fatty alcohols, fatty amines or Nonionic compounds such as fatty acid amide ethylene oxide adduct, alkylphenol ethylene oxide adduct, alkylnaphthol ethylene oxide adduct, polyethylene glycol, fatty acid ester of alkyldiethanolamine, carboxylic acid derivatives, imidazo Those such emissions derivatives of amphoteric systems. Of these, sodium alkyl sulfonate, sodium alkyl benzene sulfonate, lithium alkyl sulfonate, lithium alkyl benzene sulfonate and the like are preferable from the viewpoint of antistatic performance and transparency. Moreover, the addition amount of the antistatic agent in the anti-static agent-containing coextruded layer is usually 0.1 to 10% by weight, preferably 0.1 to 5% by weight. If the amount of the antistatic agent is too small, a sufficient antistatic function cannot be exhibited, and if it is too large, the mechanical strength of the film may be deteriorated.

  In addition, the film of the present invention may contain additives such as wax, colorant, antioxidant, and ultraviolet absorber as necessary. In addition, inert particles having an average particle size of 0.1 μm or less may be contained as long as the surface roughness is not significantly affected.

  The thickness of the film of this invention is 10-200 micrometers normally, Preferably it is 10-100 micrometers, More preferably, it is 10-75 micrometers.

  Next, although the manufacturing method of the film of this invention is demonstrated concretely, as long as the structural requirements of this invention are satisfied, it is not specifically limited to the following illustrations.

  After the polyester is dried, it is fed to an extruder and heated to a temperature equal to or higher than the melting point of each polyester to be melted. Subsequently, it extrudes from a T die as a molten sheet. Subsequently, the molten sheet is rapidly cooled to below the glass transition temperature on a rotary cooling drum to obtain an amorphous unstretched film. At this time, in order to improve the flatness of the unstretched film, the adhesion between the unstretched film and the rotating cooling drum may be improved by an electrostatic application adhesion method, a liquid application adhesion method, or the like. The obtained unstretched film is stretched in the longitudinal direction (longitudinal stretching) using a roll stretching machine to obtain a uniaxially stretched film. The drawing temperature at this time is drawn in a temperature range of (Tg-10 ° C.) to (Tg + 40 ° C.), where the glass transition temperature of the raw material resin is Tg. The draw ratio is preferably 2.5 to 7.0 times, more preferably 3.0 to 6.0 times. The longitudinal stretching may be performed in one stage or may be performed in two or more stages. Next, an aqueous coating agent is applied by a coater to provide an easy adhesion layer. Thereafter, the biaxially stretched film is obtained by stretching the uniaxially stretched film in the width direction (lateral stretching) using a tenter stretching machine. The stretching temperature at this time is in the temperature range of (Tg) to (Tg + 50 ° C.). The draw ratio is preferably 2.5 to 7.0 times, more preferably 3.5 to 6.0 times. The transverse stretching may be performed in one stage, or may be performed in two or more stages. Moreover, you may perform simultaneous biaxial stretching which performs vertical and horizontal simultaneously. And a laminated film is manufactured by heat-processing a biaxially stretched film. The heat processing temperature at this time is 130-250 degreeC. When the biaxially stretched film is heat-treated, the biaxially stretched film may be relaxed within 20%.

  According to the film of the present invention, it is possible to provide a biaxially stretched polyester film suitable as a film for forming simultaneous transfer that is less prone to problems such as blocking in the process of producing a transfer sheet and can perform fine printing. Yes, its industrial value is high.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. The measurement methods and terms used in the examples and the present invention are defined as follows.

(1) Average particle diameter The surface of the film is observed with a scanning electron microscope, and the major and minor diameters of the particles are determined for at least 100, and the arithmetic average is defined as the average particle diameter.

(2) Surface roughness Ra
Using a surface roughness measuring machine (SE-3F) manufactured by Kosaka Laboratory Ltd., the measurement is performed according to JISB-0601-1982. However, the cut-off value is 80 μm and the measurement length is 2.5 mm.

(3) Surface resistivity 16600A, which is a concentric electrode with an inner electrode 50 mm diameter and an outer electrode 70 mm diameter, manufactured by Yokogawa Hewlett-Packard Co., Ltd., is placed on the sample in an atmosphere of 23 ° C. and 50% RH, and a voltage of 100 V is applied. Then, the surface resistivity of the sample is measured with 4329A, a high resistance meter manufactured by the same company.

(4) Haze The haze is measured using a turbidimeter turbidimeter NDH-300A (manufactured by Nippon Denshoku Industries Co., Ltd.).

(5) Adhesiveness with release layer An organic solvent solution in which a melamine resin is dissolved is applied to the release layer forming surface of the film to form a release layer having a dry thickness of 1 μm, and the mold is placed on a mold by hot pressing. Observe the situation of the release layer. The criteria for determination are as follows. In the case of x, the appearance quality of the molded product is deteriorated due to peeling of the printed layer, which is a practical problem. In △, the quality is slightly inferior, so the yield is inferior, but it can be used.
○: No peeling Δ: The peeled area is 10% or less ×: The peeling exceeds 10%

(6) Transfer sheet blocking prevention property A surface of the layer A is coated with an acrylic resin, and two sheets of film are slid so that the opposite surface of the coated surface overlaps, and the friction coefficient is measured under the following conditions.
Film contact pressure: 102 gf / cm ²
Sliding speed: 20 mm / min Temperature: 23 ± 1 ° C
Humidity: 50 ± 5%
The criteria for determining blocking resistance are as follows. In the case of x, the winding of the transfer sheet causes blocking, which is a practical problem. In Δ, the transfer sheet winding workability is inferior, but it can be used.
○: Friction coefficient is 0.5 or less Δ: Friction coefficient is 0.5 to 1.0
×: Measurement is impossible due to friction coefficient exceeding 1.0 or stick-slip occurs.

Next, the polyester raw material used for an Example is demonstrated.
Polyester a: Polyethylene terephthalate resin having an intrinsic viscosity of 0.65 and a melting point of 253 ° C. synthesized by conventional polycondensation Polyester b: Amorphous having an average particle diameter of 2.5 μm synthesized by conventional polycondensation Polyethylene terephthalate resin / polyester c having an intrinsic viscosity of 0.66 containing 0.2% by weight of silica and a melting point of 253 ° C .: 1.5% of organic particles having an average particle diameter of 4.0 μm synthesized by conventional polycondensation Polyethylene terephthalate resin / polyester d having an intrinsic viscosity of 0.62 and a melting point of 253 ° C.
Polyethylene terephthalate resin / polyester e having an intrinsic viscosity of 0.65 and a melting point of 253 ° C. containing 1.0% by weight of alumina having an average particle size of 0.02 μm, synthesized by conventional polycondensation: A synthesized polyethylene terephthalate resin containing 0.9% by weight of amorphous silica having an average particle size of 3.5 μm and having an intrinsic viscosity of 0.65 and a melting point of 253 ° C.

Aqueous coating agent 1: A mixture obtained by mixing the following compounds (a), (b), (c) and (d) in a weight ratio of 47/20/30/3.
(A): Polyester obtained by reacting terephthalic acid / isophthalic acid / 5 monosodium sulfoisophthalic acid / ethylene glycol / 1.4 monobutanediol / diethylene glycol in a molar ratio of 28/20/2/35/10/5, respectively Water dispersion (b): Polymer water dispersion obtained by polymerizing methyl methacrylate / ethyl acrylate / acrylonitrile / N-methylol methacrylamide in a molar ratio of 45/45/5/5 (emulsifier: anionic surfactant) )
(C): Melamine-based crosslinking agent (hexamethoxymethylmelamine)
(D): An aqueous dispersion of silicon oxide having an average particle size of 0.06 μm

・ Water-based coating agent 2
The aqueous coating agent is a mixture in which the following compounds (a), (b) and (c) are mixed at a weight ratio of 65/5/30.
(A): Polydiallyldimethylammonium chloride (b): Partially saponified polyvinyl alcohol (degree of saponification: about 88 mol%)
(C): Methoxymethylol melamine (Bekkamin J1001 manufactured by Omemoto Ink Co., Ltd.)

Example 1:
A mixture of 95% by weight of polyester a and 5% by weight of polyester b is fed to a vented twin-screw extruder (forming layer A), and a mixture of 90% by weight of polyester a and 10% by weight of polyester c is added to another. After feeding to a twin-screw extruder with a vent (forming the B layer) and melting at a melting temperature of 280 ° C., the molten polymer from each extruder is merged with a feed block through a gear pump and a filter, and passed through a die to a casting drum. An unstretched film of two types and two layers was obtained. The unstretched film thus obtained was fed into a longitudinal stretching roll, and first stretched 3.5 times at a film temperature of 83 ° C., and then an easy-adhesive aqueous coating agent 1 was applied to one side (A layer surface) and led to a tenter. The film was stretched 4.0 times in the transverse direction at 95 ° C. to obtain a biaxially oriented film. Next, the obtained biaxially oriented film was guided to a heat setting zone and heat-treated at 220 ° C. to obtain a polyester film having a thickness described in Table 1.

Example 2:
Polyester d is supplied to a vented twin screw extruder (forms layer A), polyester a is fed to another vented twin screw extruder (forms layer B), polyester a is 90% by weight and polyester c is After feeding 10% by weight of the mixture to another vented twin-screw extruder (forming a C layer) and melting at a melting temperature of 280 ° C., the molten polymer from each extruder was fed in a feed block through a gear pump and a filter. They were merged and taken up on a casting drum through a die to obtain an unstretched film of 3 types and 3 layers. Thereafter, a film was obtained in the same manner as in Example 1.

Example 3:
A film was obtained in the same manner as in Example 2 except that the easy-adhesive aqueous coating agent 1 was applied to the surface of the A layer and then the antistatic aqueous coating agent 2 was applied to the opposite surface.

Comparative Example 1:
A film was obtained in the same manner as in Example 1 except that the aqueous coating agent 1 was not applied.

Comparative Example 2:
A mixture of 90% by weight of polyester a and 10% by weight of polyester c is fed to another vented twin screw extruder (forming layer A), and polyester a is fed to another vented twin screw extruder (forming layer B) ) And melted at a melting temperature of 280 ° C., and the melted polymer from each extruder is merged with a feed block through a gear pump and a filter, and is drawn on a casting drum through a die to obtain an unstretched film of two types and three layers. It was. Thereafter, a film was obtained in the same manner as in Example 1.

Comparative Example 3:
Vented mixture of 95% by weight of polyester a and 5% by weight of polyester b
After feeding to a shaft extruder (forming layer A) and melting at a melting temperature of 280 ° C, the molten polymer was drawn through a die through a die to a casting drum through a gear pump and a filter to obtain a single-layer unstretched film. A film was obtained in the same manner as in Example 1.

Comparative Example 4:
Polyester e was supplied to a twin screw extruder with a vent (forming layer A), polyester a was supplied to a twin screw extruder (forming layer B) and melted at a melting temperature of 280 ° C. The molten polymer was merged with a feed block via a gear pump and a filter, and was drawn on a casting drum through a die to obtain an unstretched film of two types and three layers. Thereafter, a film was obtained in the same manner as in Comparative Example 1.

  The obtained results are summarized in Table 1 and Table 2 below.

  In Examples 1, 2, and 3, the transfer sheet is excellent in anti-blocking property and adhesion to the release layer. In particular, in Examples 2 and 3, the surface roughness of the A layer is small, and the printed surface of the molded product is Appearance quality is improved. On the other hand, since Comparative Example 1 does not have a coating layer, it is inferior in easy adhesion with an acrylic resin release layer. In Comparative Example 2, the surface roughness of the A layer is large and the appearance quality of the printed surface of the molded product is inferior. Comparative Example 3 is inferior in blocking prevention with the transfer sheet. Since Comparative Example 4 has a large film surface roughness and a large film haze, it adversely affects the appearance inspection of the transfer sheet.

  The film of the present invention can be suitably used as a support film for a simultaneously molded decorative sheet used for decorating resin molded products such as electric products and automobile parts.

Claims (1)

A biaxially stretched polyester film having a coating layer, wherein the coating layer has a surface roughness Ra of 1 to 20 nm, and the other surface has a surface roughness of 25 to 100 nm or less. Biaxially stretched polyester film for transfer.