JP7083612B2 - Manufacturing method of optical laminate - Google Patents

Description

The present invention relates to a method for manufacturing an optical laminate.

A liquid crystal display device, which is a typical image display device, has polarizing films arranged on both sides of a liquid crystal cell due to its image forming method. As a method for producing a polarizing film, for example, a method has been proposed in which a laminate having a thermoplastic resin base material and a polyvinyl alcohol (PVA) -based resin layer is stretched and then immersed in a dyeing solution to obtain a polarizing film. (For example, Patent Document 1). Since such a method can obtain a thin polarizing film, it is attracting attention as it can contribute to the thinning of liquid crystal display devices in recent years.

By the way, the polarizing film is usually produced by immersing a PVA-based resin film in a bath such as a dyeing bath or a cross-linking bath and then drying it. However, as described above, when a polarizing film is produced using a thermoplastic resin base material, curl (specifically, curl that is convex toward the thermoplastic resin base material side) is likely to occur during drying, which is obtained. Poor appearance of the optical laminate (thermoplastic resin base material and polarizing film) becomes a problem. On the other hand, as a method of suppressing the curl and producing an optical laminate having an excellent appearance, a method including a drying treatment using a thermal roll has been proposed (Patent Document 2). According to the manufacturing method, an optical laminate in which curl is suppressed can be obtained. On the other hand, according to the drying treatment using the thermal roll, the transparency of the thermoplastic resin base material may decrease, and the thermoplastic resin base material is used as a protective film for the polarizing film without being peeled off. It is not preferable.

Japanese Unexamined Patent Publication No. 2001-343521 Japanese Unexamined Patent Publication No. 2013-122518

The present invention has been made to solve the above-mentioned conventional problems, and a main object thereof is to provide a method for obtaining an optical laminate in which curling is suppressed while maintaining the transparency of a thermoplastic resin base material. There is something in it.

According to the present invention, a polyvinyl alcohol-based resin layer is formed on a thermoplastic resin base material to prepare a laminate, and the polyvinyl alcohol-based resin layer is subjected to stretching treatment and dyeing treatment to prepare a polarizing film. The present invention provides a method for producing an optical laminate, which comprises contact-heating the laminate and subjecting the thermoplastic resin substrate to a crystallization treatment. The crystallization treatment includes a first crystallization treatment step in which the crystallization index of the thermoplastic resin base material is increased to a first predetermined value, and the crystallization index of the thermoplastic resin base material is set to the first predetermined value. Includes a second crystallization treatment step that results in a second predetermined value greater than the value.
In one embodiment, the first crystallization treatment step comprises contacting the laminate with a contact heating means at 50 ° C. to 95 ° C., and the first predetermined value is 0.4 or more.
In one embodiment, the second crystallization treatment step comprises contacting the laminate with a contact heating means at 96 ° C to 120 ° C, and the second predetermined value is 0.55 or more.
In one embodiment, the thermoplastic resin base material is made of a polyethylene terephthalate resin.
In one embodiment, the first and second crystallization treatment steps are performed at an atmospheric temperature of 60 ° C to 120 ° C.
In one embodiment, in the first and second crystallization treatment steps, the contact time between any one point on the surface of the laminate and the individual contact heating means is 0.1 seconds to 5 seconds, respectively. ..
In one embodiment, the shrinkage rate of the thermoplastic resin substrate by the crystallization treatment is 3% or less.
According to another aspect of the present invention, the polarization including the production of the optical laminate by the method for producing the optical laminate and the provision of an optical functional film on the polarizing film side of the obtained optical laminate. A method of manufacturing a plate is provided.

According to the present invention, when the laminate is dried, the thermoplastic resin substrate is subjected to a plurality of stages of crystallization treatment including a first crystallization treatment step and a second crystallization treatment step. Specifically, in the first crystallization treatment step, the thermoplastic resin substrate is crystallized by a relatively low temperature contact heating means so as to have a predetermined crystallization index, and then in the second crystallization treatment step. In, crystallization is further promoted by contact heating means at a relatively high temperature. When a thermoplastic resin substrate having a small crystallization index is brought into contact with a high-temperature contact heating means, cloudiness may occur. However, by contacting the thermoplastic resin substrate with a high-temperature contact heating means after the preliminary crystallization treatment as described above, the white turbidity may occur. It is possible to crystallize efficiently and sufficiently while avoiding the problem of. As a result, it is possible to obtain an optical laminate in which curling is suppressed while maintaining the transparency of the thermoplastic resin base material.

It is a schematic sectional drawing of the laminated body by a preferable embodiment of this invention. It is a schematic diagram which shows an example of the crystallization process of the manufacturing method of the optical laminated body of this invention. It is a schematic sectional drawing of the optical laminated body by a preferable embodiment of this invention. It is a graph which shows the relationship between the crystallization index of a thermoplastic resin base material, and durability. It is a photograph which shows the state of the laminated body after a durability test.

Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

In the method for producing an optical laminate of the present invention, a polyvinyl alcohol-based resin layer is formed on a thermoplastic resin base material to prepare a laminate, and the polyvinyl alcohol-based resin layer is subjected to stretching treatment and dyeing treatment. It includes producing a polarizing film and contact-heating the laminate to perform a crystallization treatment on the thermoplastic resin base material. The laminated body is typically long.

A. Preparation of Laminated Body FIG. 1 is a schematic cross-sectional view of the laminated body according to a preferred embodiment of the present invention. The laminate 10 has a thermoplastic resin base material 11 and a PVA-based resin layer 12, and is manufactured by forming the PVA-based resin layer 12 on the thermoplastic resin base material. As the method for forming the PVA-based resin layer 12, any suitable method can be adopted. Preferably, the coating liquid containing the PVA-based resin is applied onto the thermoplastic resin base material 11 and dried to form the PVA-based resin layer 12.

The thermoplastic resin base material preferably has a crystallization index (before crystallization treatment) of 0.16 or less, more preferably 0.12 or less. In such a thermoplastic resin base material, crystallization may be promoted in the drying treatment and the crystallization index may increase. As a result, the rigidity of the thermoplastic resin base material is increased, and the PVA-based resin layer is in a state of being able to withstand shrinkage due to drying, and curling is suppressed. Further, by using such a thermoplastic resin base material, the laminated body can be satisfactorily stretched. Specifically, when the laminate is immersed in a stretching bath (for example, an aqueous boric acid solution) and stretched in water as described later, the stretching tension is reduced and the stretchability is improved.

The thermoplastic resin base material preferably has a water absorption rate of 0.2% or more, more preferably 0.3% or more. The thermoplastic resin substrate absorbs water, and the water can act as a plasticizer to plasticize. As a result, the drawing stress can be significantly reduced, and the drawing can be performed at a high magnification. On the other hand, the water absorption rate of the thermoplastic resin base material is preferably 3.0% or less, more preferably 1.0% or less. By using such a thermoplastic resin base material, it is possible to prevent problems such as deterioration of the dimensional stability of the thermoplastic resin base material at the time of manufacture and deterioration of the appearance of the obtained polarizing film. In addition, it is possible to prevent the base material from breaking during stretching in water and the PVA-based resin layer from peeling off from the thermoplastic resin base material. The water absorption rate of the thermoplastic resin base material can be adjusted, for example, by introducing a modifying group into the constituent material. The water absorption rate is a value obtained according to JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 170 ° C. or lower. By using such a thermoplastic resin base material, it is possible to sufficiently secure the stretchability of the laminated body while suppressing the crystallization of the PVA-based resin layer. Further, considering that the thermoplastic resin base material is plasticized with water and well stretched in water, the temperature is more preferably 120 ° C. or lower. On the other hand, the glass transition temperature of the thermoplastic resin base material is preferably 60 ° C. or higher. By using such a thermoplastic resin base material, the thermoplastic resin base material is deformed (for example, unevenness, tarmi, wrinkles, etc.) when the coating liquid containing the PVA-based resin is applied and dried. It is possible to satisfactorily produce a laminated body by preventing the above-mentioned problems. Further, the PVA-based resin layer can be well stretched at a suitable temperature (for example, about 60 ° C.). The glass transition temperature of the thermoplastic resin base material can be adjusted, for example, by heating with a crystallization material that introduces a modifying group into the constituent material. The glass transition temperature (Tg) is a value obtained according to JIS K 7121.

Any suitable material may be adopted as the constituent material of the thermoplastic resin base material. Preferably, a material is used that gives a resin substrate having a desired crystallization index. The crystallization index can be adjusted, for example, by introducing a modifying group into the constituent material. Amorphous (non-crystallized) polyethylene terephthalate resin is preferably used as the constituent material of the thermoplastic resin base material. Among them, an amorphous (difficult to crystallize) polyethylene terephthalate resin is particularly preferably used. Specific examples of the amorphous polyethylene terephthalate resin include a copolymer further containing isophthalic acid and / or a cyclohexanedicarboxylic acid as a dicarboxylic acid, and a copolymer further containing cyclohexanedimethanol or diethylene glycol as a glycol.

In a preferred embodiment, the thermoplastic resin substrate is composed of a polyethylene terephthalate resin having an isophthalic acid unit. This is because such a thermoplastic resin base material is extremely excellent in stretchability and can suppress crystallization during stretching. It is considered that this is because the introduction of the isophthalic acid unit gives a large bending to the backbone. The polyethylene terephthalate resin has a terephthalic acid unit and an ethylene glycol unit. The content ratio of the isophthalic acid unit is preferably 0.1 mol% or more, more preferably 1.0 mol% or more, based on the total of all repeating units. This is because a thermoplastic resin base material having extremely excellent stretchability can be obtained. On the other hand, the content ratio of the isophthalic acid unit is preferably 20 mol% or less, more preferably 10 mol% or less, based on the total of all repeating units. By setting such a content ratio, the crystallization index can be satisfactorily increased in the crystallization treatment described later.

The thickness of the thermoplastic resin substrate before stretching is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm. If it is less than 20 μm, it may be difficult to form a PVA-based resin layer. If it exceeds 300 μm, for example, in the underwater stretching treatment described later, it may take a long time for the thermoplastic resin base material to absorb water, and an excessive load may be required for stretching.

As the PVA-based resin, any suitable resin can be adopted. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymers can be mentioned. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer is obtained by saponifying the ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. .. The degree of saponification can be determined according to JIS K 6726-1994. By using a PVA-based resin having such a saponification degree, a polarizing film having excellent durability can be obtained. If the degree of saponification is too high, gelation may occur.

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the intended purpose. The average degree of polymerization is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average degree of polymerization can be determined according to JIS K 6726-1994.

The coating liquid is typically a solution in which the PVA-based resin is dissolved in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Among these, water is preferable. The PVA-based resin concentration of the solution is preferably 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, it is possible to form a uniform coating film in close contact with the thermoplastic resin base material.

The coating liquid may contain additives. Examples of the additive include a plasticizer, a surfactant and the like. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. Examples of the surfactant include nonionic surfactants. These can be used for the purpose of further improving the uniformity, dyeability, and stretchability of the obtained PVA-based resin layer. In addition, examples of the additive include an easy-adhesive component. By using the easy-adhesion component, the adhesion between the resin base material and the PVA-based resin layer can be improved. As a result, for example, it is possible to suppress problems such as peeling of the PVA-based resin layer from the resin base material, and to perform dyeing and stretching in water, which will be described later, satisfactorily. As the easy-adhesion component, for example, modified PVA such as acetoacetyl-modified PVA is used. Furthermore, examples of the additive include halides such as potassium iodide, sodium iodide, lithium iodide, and sodium chloride, urea, and the like. By adding these, optical characteristics (for example, simple substance transmittance) can be improved. The blending amount of the additive can be appropriately set according to the purpose and the like.

Any appropriate method can be adopted as the coating method of the coating liquid. For example, a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a knife coating method (comma coating method, etc.) and the like can be mentioned.

The coating / drying temperature of the coating liquid is preferably 50 ° C. or higher.

The thickness of the PVA-based resin layer before stretching is preferably 3 μm to 40 μm, more preferably 3 μm to 20 μm.

Before forming the PVA-based resin layer, the thermoplastic resin base material may be surface-treated (for example, corona treatment or the like), or the easy-adhesive layer may be formed on the thermoplastic resin base material. By performing such a treatment, the adhesion between the thermoplastic resin base material and the PVA-based resin layer can be improved.

B. Preparation of Polarizing Film A polarizing film is typically produced by subjecting a PVA-based resin layer formed on the thermoplastic resin substrate to a stretching treatment and a dyeing treatment. In addition to the stretching treatment and the dyeing treatment, the PVA-based resin layer may be appropriately subjected to a treatment for forming the PVA-based resin layer into a polarizing film. Examples of the treatment for forming the polarizing film include insolubilization treatment, cross-linking treatment, cleaning treatment and the like. These processes can be selected according to the purpose. In addition, processing conditions such as processing order, processing timing, and number of processing can be appropriately set. Hereinafter, each process will be described.

(Dyeing process)
The dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance. It is preferably carried out by adsorbing a dichroic substance on the PVA-based resin layer. Examples of the adsorption method include a method of immersing a PVA-based resin layer (laminate) in a dyeing solution containing a dichroic substance, a method of applying the above-mentioned dyeing solution to the PVA-based resin layer, and the above-mentioned dyeing solution being PVA-based. Examples thereof include a method of spraying on the resin layer. A method of immersing the laminate in the dyeing solution is preferable. This is because the dichroic substance can be adsorbed well.

When iodine is used as the dichroic substance, the staining solution is preferably an aqueous iodine solution. The blending amount of iodine is preferably 0.1 part by weight to 0.5 part by weight with respect to 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add iodide to the aqueous iodine solution. Examples of iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. And so on. Among these, potassium iodide is preferable. The blending amount of the iodide is preferably 0.02 parts by weight to 20 parts by weight, and more preferably 0.1 parts by weight to 10 parts by weight with respect to 100 parts by weight of water.

The liquid temperature at the time of dyeing the dyeing liquid is preferably 20 ° C. to 50 ° C. in order to suppress the dissolution of the PVA-based resin. When the PVA-based resin layer is immersed in the dyeing solution, the immersion time is preferably 5 seconds to 5 minutes in order to secure the transmittance of the PVA-based resin layer. Further, the dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the degree of polarization or the single transmittance of the finally obtained polarizing film is within a predetermined range. In one embodiment, the immersion time is set so that the degree of polarization of the obtained polarizing film is 99.98% or more. In another embodiment, the immersion time is set so that the single transmittance of the obtained polarizing film is 40% to 45%.

(Stretching treatment)
Any suitable method can be adopted as the method for stretching the laminated body. Specifically, it may be fixed-end stretching (for example, a method using a tenter stretching machine) or free-end stretching (for example, a method of uniaxial stretching through a laminate between rolls having different peripheral speeds). Further, simultaneous biaxial stretching (for example, a method using a simultaneous biaxial stretching machine) may be used, or sequential biaxial stretching may be used. The stretching of the laminate may be carried out in one step or in multiple steps. In the case of performing in multiple stages, the draw ratio (maximum draw ratio) of the laminated body described later is the product of the draw ratios of each stage.

The stretching treatment may be performed by an underwater stretching method in which the laminated body is immersed in a stretching bath, or may be an air stretching method. Preferably, the underwater stretching treatment is performed at least once, and more preferably, the underwater stretching treatment and the air stretching treatment are combined. According to the underwater stretching, the PVA-based resin layer can be stretched at a temperature lower than the glass transition temperature (typically, about 80 ° C.) of the resin substrate or the PVA-based resin layer, while suppressing the crystallization of the PVA-based resin layer. , Can be stretched at high magnification. As a result, it is possible to manufacture a polarizing film having excellent optical characteristics (for example, degree of polarization).

Any appropriate direction can be selected as the stretching direction of the laminated body. In one embodiment, the elongated laminate is stretched in the longitudinal direction. Specifically, the laminated body is transported in the longitudinal direction, and the transport direction (MD) thereof. In another embodiment, the elongated laminate is stretched in the width direction. Specifically, the laminated body is transported in the longitudinal direction, and the direction is orthogonal to the transport direction (MD) (TD).

The stretching temperature of the laminate can be set to an arbitrary appropriate value depending on the forming material of the resin base material, the stretching method, and the like. When the aerial stretching method is adopted, the stretching temperature is preferably the glass transition temperature (Tg) or higher of the resin base material, more preferably the glass transition temperature (Tg) of the resin base material (Tg) + 10 ° C. or higher, and particularly preferably Tg + 15 ° C. That is all. On the other hand, the stretching temperature of the laminated body is preferably 170 ° C. or lower. By stretching at such a temperature, it is possible to suppress the rapid progress of crystallization of the PVA-based resin and suppress defects due to the crystallization (for example, hindering the orientation of the PVA-based resin layer due to stretching). can.

When the underwater stretching method is adopted as the stretching method, the liquid temperature of the stretching bath is preferably 40 ° C. to 85 ° C., more preferably 50 ° C. to 85 ° C. At such a temperature, the PVA-based resin layer can be stretched at a high magnification while suppressing dissolution. Specifically, as described above, the glass transition temperature (Tg) of the resin base material is preferably 60 ° C. or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40 ° C., there is a possibility that the resin substrate cannot be stretched satisfactorily even if the plasticization of the resin base material by water is taken into consideration. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and there is a possibility that excellent optical characteristics cannot be obtained.

When the underwater stretching method is adopted, it is preferable to immerse the laminate in a boric acid aqueous solution and stretch it (boric acid water stretching). By using the boric acid aqueous solution as the stretching bath, it is possible to impart rigidity to withstand the tension applied during stretching and water resistance that does not dissolve in water to the PVA-based resin layer. Specifically, boric acid can generate a tetrahydroxyboric acid anion in an aqueous solution and crosslink with a PVA-based resin by hydrogen bonding. As a result, the PVA-based resin layer can be imparted with rigidity and water resistance, can be stretched satisfactorily, and a polarizing film having excellent optical characteristics can be produced.

The boric acid aqueous solution is preferably obtained by dissolving boric acid and / or borate in water as a solvent. The boric acid concentration is preferably 1 part by weight to 10 parts by weight with respect to 100 parts by weight of water. By setting the boric acid concentration to 1 part by weight or more, the dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film having higher characteristics can be produced. In addition to boric acid or borate, an aqueous solution obtained by dissolving a boron compound such as borax, glioxal, glutaraldehyde or the like in a solvent can also be used.

Preferably, the iodide is added to the stretching bath (boric acid aqueous solution). By blending iodide, the elution of iodine adsorbed on the PVA-based resin layer can be suppressed. Specific examples of iodide are as described above. The concentration of iodide is preferably 0.05 parts by weight to 15 parts by weight, and more preferably 0.5 parts by weight to 8 parts by weight with respect to 100 parts by weight of water.

The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The draw ratio (maximum draw ratio) of the laminated body is preferably 5.0 times or more with respect to the original length of the laminated body. Such a high draw ratio can be achieved, for example, by adopting an underwater stretching method (boric acid underwater stretching). In the present specification, the "maximum draw ratio" means the draw ratio immediately before the laminate breaks, and separately confirms the draw ratio at which the laminate breaks and means a value 0.2 lower than that value. ..

Preferably, the underwater stretching treatment is performed after the dyeing treatment.

(Insolubilization treatment)
The insolubilization treatment is typically performed by immersing a PVA-based resin layer in a boric acid aqueous solution. In particular, when the underwater stretching method is adopted, water resistance can be imparted to the PVA-based resin layer by subjecting it to an insolubilization treatment. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 4 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the insolubilizing bath (boric acid aqueous solution) is preferably 20 ° C to 40 ° C. Preferably, the insolubilization treatment is performed after the laminate is prepared and before the dyeing treatment or the underwater stretching treatment.

(Crosslinking)
The cross-linking treatment is typically performed by immersing a PVA-based resin layer in an aqueous boric acid solution. By applying the cross-linking treatment, water resistance can be imparted to the PVA-based resin layer. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 4 parts by weight with respect to 100 parts by weight of water. Further, when the cross-linking treatment is performed after the dyeing treatment, it is preferable to further add iodide. By blending iodide, the elution of iodine adsorbed on the PVA-based resin layer can be suppressed. The blending amount of iodide is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of water. Specific examples of iodide are as described above. The liquid temperature of the cross-linked bath (boric acid aqueous solution) is preferably 20 ° C to 50 ° C. Preferably, the crosslinking treatment is performed before the underwater stretching treatment. In a preferred embodiment, the dyeing treatment, the crosslinking treatment and the underwater stretching treatment are performed in this order.

(Washing process)
The cleaning treatment is typically performed by immersing a PVA-based resin layer in an aqueous potassium iodide solution.

The polarizing film produced through the above-mentioned various treatments is substantially a PVA-based resin film in which a dichroic substance is adsorbed and oriented. The thickness of the polarizing film is typically 25 μm or less, preferably 15 μm or less, more preferably 10 μm or less, still more preferably 7 μm or less, and particularly preferably 5 μm or less. On the other hand, the thickness of the polarizing film is preferably 0.5 μm or more, more preferably 1.5 μm or more. The polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The simple substance transmittance of the polarizing film is preferably 40.0% or more, more preferably 41.0% or more, still more preferably 42.0% or more, and particularly preferably 43.0% or more. The degree of polarization of the polarizing film is preferably 99.8% or more, more preferably 99.9% or more, still more preferably 99.95% or more.

C. Crystallization treatment The crystallization treatment is carried out by bringing the laminate into contact with the contact heating means. By bringing the laminate into contact with the contact heating means, the drying of the laminate and the crystallization of the thermoplastic resin base material proceed, and as a result, curling can be suppressed and an optical laminate having an excellent appearance can be produced.

Examples of the contact heating means include a heat roll (heated transfer roll), a heat plate, a heating wire, and the like. Of these, thermal rolls are preferred. By drying the laminated body along the hot roll (heat roll drying method), the crystallization of the thermoplastic resin base material can be efficiently promoted and the crystallization index can be increased. As a result, the rigidity of the thermoplastic resin base material is increased, and the PVA-based resin layer is in a state of being able to withstand shrinkage due to drying, and curling is suppressed. Further, by using the heat roll, the laminated body can be dried while being maintained in a flat state, so that not only curling but also wrinkles can be suppressed. The contact surface of the laminate with the contact heating means is not particularly limited, but preferably the contact heating means and the thermoplastic resin base material surface of the laminate are brought into contact with each other.

In the present invention, the crystallization treatment sets the crystallization index of the thermoplastic resin base material to the first crystallization treatment step of increasing the crystallization index of the thermoplastic resin base material to a first predetermined value and the crystallization index of the thermoplastic resin base material. 1 Includes a second crystallization treatment step of setting a second predetermined value larger than the predetermined value. If necessary, it may include one or more additional crystallization treatment steps that further increase the crystallization index of the thermoplastic resin substrate. Hereinafter, the crystallization treatment using a heat roll as the contact heating means will be described, but the same description can be applied to the crystallization treatment using a contact heating means other than the heat roll.

The first crystallization treatment step typically comprises contacting the laminate with at least one heat roll at 50 ° C. to 95 ° C., preferably the laminate at a plurality of 50 ° C. to 95 ° C. Includes contact with a thermal roll. By using a plurality of thermal rolls, the crystallinity can be precisely controlled.

The temperature of the heat roll in the first crystallization treatment step is preferably 60 ° C. to 93 ° C., more preferably 80 ° C. to 90 ° C. The number of heat rolls is not particularly limited, and is usually 2 to 20, preferably 3 to 15. The contact time between the laminate and the individual thermal rolls is preferably 0.1 seconds to 5 seconds, respectively.

When using multiple heat rolls, these heat rolls can be set to the same or different temperatures. When the temperature is set to a different temperature, it is preferable to set the temperature so that the temperature increases from the heat roll arranged on the upstream side of the process toward the heat roll arranged on the downstream side. Contacting the laminated body in order from the heat roll having the lowest temperature may be effective in suppressing shrinkage in the width direction of the laminated body, curling of the end portion, and the like.

The first predetermined value, that is, the crystallization index of the thermoplastic resin substrate at the end of the first crystallization treatment step is, for example, 0.35 or more, preferably 0.38 or more, more preferably 0.40. The above (for example, 0.43 or more or 0.45 or more). By setting such a crystallization index and proceeding to the second crystallization treatment step, the thermoplastic resin substrate becomes cloudy even when it is brought into contact with a hot roll at a high temperature (for example, 96 ° C. or higher). It is possible to improve the durability by advancing crystallization while preventing the above. On the other hand, the upper limit of the first predetermined value is appropriately set in consideration of the crystallization index finally obtained (after the second crystallization treatment step), and is not particularly limited, but the productivity is increased. From the viewpoint, it can be, for example, 0.55 or less.

The second crystallization treatment step typically comprises contacting the laminate with at least one thermal roll at 96 ° C to 120 ° C. The temperature of the second heat roll is preferably 100 ° C. to 115 ° C., more preferably 105 ° C. to 115 ° C. The number of heat rolls is not particularly limited, and is usually 1 to 10, preferably 1 to 5. The contact time between the laminate and the heat roll (contact time with each heat roll when there are a plurality of them) is preferably 0.1 seconds to 5 seconds.

The second predetermined value, that is, the crystallization index of the thermoplastic resin base material at the end of the second crystallization treatment step is, for example, 0.52 or more, preferably 0.55 or more, and more preferably 0. .60 or more (for example, 0.65 or more or 0.70 or more). Sufficient durability can be obtained by using such a crystallization index. On the other hand, the upper limit of the second predetermined value is not particularly limited, but may be, for example, 0.8 or less from the viewpoint of maintaining the productivity and the appearance of the laminated body in a preferable state.

In the second crystallization treatment step, the crystallization index of the thermoplastic resin substrate is preferably increased by 0.12 or more, more preferably 0.15 to 0.30, from the first predetermined value. High productivity can be achieved by efficiently advancing crystallization using a high-temperature thermal roll.

To control the crystallization index of the thermoplastic resin substrate by adjusting the temperature of the thermal rolls, the number of thermal rolls, the contact time with the thermal rolls, etc. in the first crystallization treatment and the second crystallization treatment. Can be done. The total contact time (total contact time) between the laminate and the thermal roll in the first crystallization treatment and the second crystallization treatment is preferably 3 seconds to 50 seconds, more preferably 4 seconds to 20 seconds, and further. It is preferably 5 to 15 seconds.

FIG. 2 is a schematic view showing an example of the crystallization treatment. In the illustrated example, the transfer rolls R1 to R4 are provided in the oven 200a, and the transfer rolls R5 to R6 are provided in the oven 200b. Two or more of the transport rolls R1 to R4 are heated to 50 ° C. to 95 ° C. to form the first heat roll, and at least one of R5 to R6 is heated to 96 ° C. to 120 ° C. to form the second heat roll. Has been done. The thermoplastic resin base material is crystallized to a desired crystallization index while the laminate 10 is transported by the transport rolls R1 to R4 and the guide rolls G1 to G4 heated to a predetermined temperature, and the first crystallization treatment is performed. Then, while transporting by the transport rolls R5 to R6 and the guide rolls G5 to G6, the crystallization index of the thermoplastic resin substrate is further increased to perform the second crystallization treatment. The laminated body 10 having completed the first and second crystallization treatments is sent out to a straight path via guide rolls G7 to G8. Note that, unlike the illustrated example, the first crystallization treatment and the second crystallization treatment may be performed in the same oven (that is, at the same ambient temperature), and the first crystallization treatment or the second crystallization treatment may be performed. Part of the crystallization process may be carried out at different temperatures.

The heat roll may be provided in a heating furnace (for example, an oven) as shown in the illustrated example, or may be provided in a normal production line (in a room temperature environment) unlike the illustrated example. Preferably, it is provided in a heating furnace. The atmospheric temperature in the heating furnace is preferably 60 ° C. to 120 ° C., more preferably 80 ° C. to 110 ° C. The heating furnace may be provided with a blowing means. By using both hot roll drying and hot air drying together, a steep temperature change between the hot rolls can be suppressed, and shrinkage in the width direction can be easily controlled.

Shrinkage rate of the thermoplastic resin base material by the above crystallization treatment [(width of the thermoplastic resin base material before the first crystallization treatment-width of the thermoplastic resin base material after the first crystallization treatment) / 1st The width of the thermoplastic resin base material before the crystallization treatment × 100] is preferably 3% or less, more preferably 2% or less.

Preferably, the stretching treatment in the preparation of the polarizing film includes an underwater stretching treatment (boric acid underwater stretching) treatment. According to such an embodiment, as described above, a high draw ratio can be achieved and the orientation of the thermoplastic resin base material can be improved. When heat is applied to the thermoplastic resin substrate by the crystallization treatment in a state of high orientation, crystallization may proceed rapidly and the crystallization index may increase remarkably. The crystallization index of the thermoplastic resin base material after the underwater stretching (boric acid underwater stretching) treatment is preferably about 0.25 to 0.35.

D. Optical Laminate The optical laminate obtained by the production method of the present invention includes the polarizing film and the thermoplastic resin substrate having a predetermined crystallization index. The optical laminate may further include other members as needed.

3A and 3B are schematic cross-sectional views of an optical laminate according to one preferred embodiment, respectively. The optical laminate 100a has a thermoplastic resin base material 11', a polarizing film 12', an adhesive layer 13, and a separator 14 in this order. The optical laminate 100b has a thermoplastic resin base material 11', a polarizing film 12', an adhesive layer 15, an optical functional film 16, an adhesive layer 13, and a separator 14 in this order. In the present embodiment, the thermoplastic resin base material is used as it is as an optical member without being peeled from the obtained polarizing film 12'. The thermoplastic resin base material 11'can function as, for example, a protective film for the polarizing film 12'.

The stacking of each layer constituting the optical laminate is not limited to the illustrated example, and any suitable adhesive layer or adhesive layer may be used. The pressure-sensitive adhesive layer is typically formed of an acrylic pressure-sensitive adhesive. The adhesive layer is typically formed of a PVA-based adhesive. The optical functional film can function as, for example, a polarizing film protective film, a retardation film, and the like. The optical laminate (polarizing plate) having the optical functional film (for example, a polarizing film protective film) is, for example, an arbitrary suitable pressure-sensitive adhesive layer or adhesion to the polarizing film side of the optical laminate subjected to the crystallization treatment. It can be obtained by laminating an optical functional film via an agent layer.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The measurement method for each characteristic is as follows.
1. 1. The thickness was measured using a digital micrometer (manufactured by Anritsu, product name "KC-351C").
2. 2. Crystallization index of thermoplastic resin substrate Using FT-IR (Fourier transform infrared spectrophotometer) manufactured by PerkinElmer, a multiple total reflection device (ATR) was attached, and the measurement was performed with a resolution of 4 cm ^-1 and a total of 32 times. The crystallization index of the PET film was measured by the following formula using the peak intensity of the peak 1340 cm ^-1 derived from the crystal band of the PET spectrum and the peak intensity of 1410 cm ^-1 which is regarded as the non-bichromatic band of the benzene ring.
Crystallization index = peak intensity of 1340 cm ^-1 / peak intensity of 1410 cm ^-1 3. Glass transition temperature (Tg) of thermoplastic resin substrate
It was measured according to JIS K 7121.

[Example 1]
As the thermoplastic resin base material, amorphous polyethylene terephthalate (IPA copolymerized PET) having a thickness of 100 μm, a crystallization index of 0 to 0.1, and an isophthalic acid unit having a Tg of 75 ° C. copolymerized in an amount of 5 mol% was used. The surface of this film was subjected to corona treatment (58 W / m ² / min). Acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name: Gosefimer Z200, average degree of polymerization: 1200, degree of saponification: 98.5 mol% or more, degree of acetoacetylation: 5%) and PVA (average). A PVA-based resin containing (polymerization degree: 4200, saponification degree: 99.2 mol%) at a ratio of 1: 9 was prepared, and 13 parts by weight of potassium iodide was added to 100 parts by weight of the PVA-based resin. A PVA-based resin aqueous solution was prepared (PVA-based resin concentration: 5.5% by weight). This aqueous solution was applied to the corona-treated surface of the resin substrate so that the film thickness after drying was 13 μm, and dried in an atmosphere of 60 ° C. for 10 minutes by hot air drying to prepare a laminate. The obtained laminate was first stretched 2.4 times at 140 ° C. in the air (aerial auxiliary stretching).

Next, the laminate was immersed in an insolubilizing bath at a liquid temperature of 30 ° C. (a boric acid aqueous solution obtained by blending 3 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (insolubilization treatment).
Then, it was dyed in a dyeing bath containing iodine and potassium iodide at a liquid temperature of 30 ° C., and immersed so that the single transmittance (Ts) of the finally obtained polarizing film was 40 to 45%. The dyeing solution uses water as a solvent, the iodine concentration is in the range of 0.1 to 0.4% by weight, the potassium iodide concentration is in the range of 0.7 to 2.8% by weight, and iodine and potassium iodide are used. The ratio of the concentrations of iodine was 1: 7 (staining treatment).
Next, the laminate was immersed in a boric acid aqueous solution having a liquid temperature of 30 ° C. for 60 seconds, and the PVA resin layer on which iodine was adsorbed was subjected to a crosslinking treatment. The boric acid aqueous solution in this step had a boric acid content of 3 parts by weight with respect to 100 parts by weight of water and a potassium iodide content of 3 parts by weight with respect to 100 parts by weight of water (crosslinking treatment).
Then, the laminate is immersed in an aqueous solution of boric acid having a liquid temperature of 70 ° C. (an aqueous solution obtained by blending 4 parts by weight of boric acid and 5 parts by weight of potassium iodide with respect to 100 parts by weight of water). However, uniaxial stretching was performed in the vertical direction between rolls having different peripheral speeds (underwater stretching treatment). The draw ratio at this time was set to 2.3 times (final draw ratio 5.5 times).
Then, the laminate was washed with an aqueous solution obtained by blending 4 parts by weight of potassium iodide with respect to 100 parts by weight of water (washing step).
Then, as shown in FIG. 2, the laminate was dried and the thermoplastic resin base material was crystallized while being conveyed by a thermal roll provided in the oven. Here, the temperature of R1 to R4 was set to 85 ° C., the temperature of R5 was set to 100 ° C., and the temperature of R6 was set to 50 ° C. Further, hot air is blown so that the atmospheric temperature in the oven for the first crystallization treatment becomes 90 ° C., and hot air is blown so that the atmospheric temperature in the oven for the second crystallization treatment becomes 95 ° C. I blew. The contact time between the laminate and the thermal roll (contact time between any one point of the laminate and each thermal roll) is 2.5 seconds (10 seconds in total) for each of the thermal rolls R1 to R4. The contact time with the heat roll R5 was 2.5 seconds.
In this way, a polarizing film having a thickness of 5 μm was produced on the thermoplastic resin base material (target transmittance: 42.5%). The crystallization index of the thermoplastic resin base material after the underwater stretching treatment was about 0.28.
Subsequently, a protective film (acrylic, thickness 40 μm) was bonded to the polarizing film side of the obtained laminate via a UV curable adhesive by a roll-to-roll method.

[Example 2]
The temperature of the first roll R1 from the upstream side is turned off, the temperature of the rolls R2 to R4 is set to 90 ° C., and the contact time between the laminate and the thermal rolls R2 to R4 is 3 seconds (total: 9 seconds). The contact time with the heat rolls R5 to R6 was set to 3 seconds (total: 6 seconds), and hot air was blown so that the ambient temperature in the oven for the second crystallization treatment was 100 ° C. An optical laminate was produced in the same manner as in Example 1 except for the above.

[Example 3]
The temperature of R5 was set to 105 ° C., and hot air was blown so that the temperature of the atmosphere in the oven for the first crystallization treatment was 95 ° C., and the atmosphere in the oven for the second crystallization treatment was set. An optical laminate was produced in the same manner as in Example 1 except that hot air was blown so that the temperature became 100 ° C.

[Example 4]
The temperature of the heat rolls R1 to R4 was set to 65 ° C., the temperature of R5 was set to 110 ° C., and hot air was blown so that the atmospheric temperature in the oven for the second crystallization treatment was 100 ° C. An optical laminate was produced in the same manner as in Example 1 except for the above.

[Example 5]
Optical lamination in the same manner as in Example 1 except that the temperature of R5 was set to 90 ° C. and hot air was blown so that the atmospheric temperature in the oven for the second crystallization treatment was 90 ° C. The body was made.

[Comparative Example 1]
In the oven in which hot air was blown so that the atmospheric temperature became 60 ° C., the laminate was brought into contact with one hot roll (110 ° C.) for 3 seconds for crystallization treatment, except that the crystallization treatment was performed. An optical laminate was produced in the same manner.

The evaluation results of the durability of the optical laminate and the transparency of the thermoplastic resin substrate obtained in each Example and Comparative Example are shown in Table 1 together with the crystallization index and the treatment conditions after each crystallization treatment. The method for evaluating the durability and the transparency of the thermoplastic resin base material is as follows.
1. 1. Durability Acrylic adhesive is laminated on the acrylic protective film surface of the obtained optical laminate, laminated to glass to produce a polarizing plate with glass, and placed in a constant temperature and humidity chamber at 60 ° C and 90% RH for 500 hours. Then, it was observed whether or not the thermoplastic resin base material was peeled off from the end portion of the optical laminate. When peeling was confirmed, the peeling amount (mm) of the thermoplastic resin base material from the end of the optical laminate was measured.
2. 2. Transparency of Thermoplastic Resin Base Material The haze measured in accordance with JIS K7136 for the obtained optical laminate was evaluated as the haze of the thermoplastic resin base material according to the following criteria.
Haze is less than 2% ... Excellent Haze is 2% or less Less than 3% ... Good Haze is 3% or more ... Bad

All of the optical laminates of Examples 1 to 5 had a haze of less than 3, and the transparency of the thermoplastic resin substrate was maintained. Among them, the crystallization index of the thermoplastic resin base material after the first crystallization treatment is 0.40 or more, and the crystallization index of the thermoplastic resin base material after the second crystallization treatment is 0.55 or more. In Examples 1 to 3, the durability of the optical laminate was also excellent, and the haze of the thermoplastic resin base material was 1.5% or less, and the appearance was extremely good. The optical laminate of Example 5 had an extremely excellent appearance with a haze of the thermoplastic resin base material of 1.0% or less, but in the durability test, it was peeled off from the end of the thermoplastic resin base material. Was slightly confirmed. On the other hand, in the optical laminate of Comparative Example 1 which was not subjected to the stepwise crystallization treatment, the haze of the thermoplastic resin base material was 3% or more, and cloudiness occurred.

[Reference Example 1]
The crystallization index of the thermoplastic resin substrate was 0.35, 0.43, 0.51, 0.55, or 0 in the same manner as in Example 1 except that the crystallization treatment was performed under various conditions. Optical laminates of .60 to 0.69 were obtained. The optical laminate was placed in a constant temperature bath at 80 ° C., a constant temperature bath at 85 ° C., a constant temperature and humidity chamber at 60 ° C. and 90% RH, or a constant temperature and humidity chamber at 60 ° C. and 95% RH. The amount of peeling (mm) from the end of the thermoplastic resin base material in the laminated body was measured. The results are shown in FIG. Further, photographs of the optical laminate without peeling and photographs of the optical laminate with peeling are shown in FIGS. 5 (a) and 5 (b), respectively.

As shown in FIG. 4, when the crystallization index was 0.55 or more, the thermoplastic resin base material did not peel off.

The polarizing film of the present invention is suitably used for liquid crystal panels such as liquid crystal televisions, liquid crystal displays, mobile phones, digital cameras, video cameras, portable game machines, car navigation systems, copy machines, printers, fax machines, watches, and microwave ovens.

10 Laminated body 11 Thermoplastic resin base material 12 Polyvinyl alcohol-based resin layer 100 Optical laminated body

Claims (7)

To form a laminate by forming a polyvinyl alcohol-based resin layer on a thermoplastic resin base material having a crystallization index of 0.16 or less .
The polyvinyl alcohol-based resin layer is subjected to stretching treatment and dyeing treatment to prepare a polarizing film, and
A method for producing an optical laminate, which comprises contact-heating the laminate and subjecting the thermoplastic resin substrate to a crystallization treatment.
The crystallization treatment increases the crystallization index of the thermoplastic resin base material to a first predetermined value, and the crystallization treatment index of the thermoplastic resin base material is set to the first predetermined value. Including a second crystallization treatment step to make the second predetermined value larger than the value.
The thermoplastic resin base material is composed of a polyethylene terephthalate resin.
The first crystallization treatment step comprises contacting the laminate with a contact heating means at 50 ° C. to 95 ° C.
The first predetermined value is 0.40 to 0.55, and the first predetermined value is 0.40 to 0.55.
The second crystallization treatment step comprises contacting the laminate with a contact heating means at 96 ° C to 120 ° C.
The second predetermined value is 0.52 to 0.8, and is
A method for manufacturing an optical laminate , wherein the difference between the second predetermined value and the first predetermined value is 0.12 or more . The method for manufacturing an optical laminate according to claim 1, wherein the first predetermined value is 0.43 to 0.55 . The method for manufacturing an optical laminate according to claim 1 or 2, wherein the second predetermined value is 0.55 to 0.8 . The method for producing an optical laminate according to any one of claims 1 to 3 , wherein the first and second crystallization treatment steps are performed at an atmospheric temperature of 60 ° C to 120 ° C. According to claim 1, in the first and second crystallization treatment steps, the contact time between any one point on the surface of the laminate and each of the contact heating means is 0.1 seconds to 5 seconds, respectively. 4. The method for manufacturing an optical laminate according to any one of 4. The method for producing an optical laminate according to any one of claims 1 to 5 , wherein the shrinkage rate of the thermoplastic resin base material by the crystallization treatment is 3% or less. To manufacture the optical laminate by the manufacturing method according to any one of claims 1 to 6 , and to manufacture the optical laminate.
A method for manufacturing a polarizing plate, which comprises providing an optical functional film on the polarizing film side of the obtained optical laminate.

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