JP2012197547A - Synthetic leather - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide synthetic leather including a foam layer formed by a dry method that may be manufactured by a method simpler than a conventional manufacture method without requiring a curing period.SOLUTION: Synthetic leather comprises at least a surface layer, a foam layer and a fibrous substrate. The foam layer is made of a urethane prepolymer having an isocyanate group at a terminal and including 2 to 6 wt.% of the isocyanate group. After applying the urethan prepolymer, 15 to 40% of the isocyanate group of the urethane prepolymer is reacted in a heating atmosphere, and the resultant is then adhered to the fibrous substrate, and thereafter, the rest of the isocyanate group is reacted to be cured in a humidified heating atmosphere.

Description

  The present invention relates to a synthetic leather having a texture very similar to that of natural leather.

Conventionally, artificial leather and synthetic leather have been used as substitutes for natural leather. Artificial leather and synthetic leather have been proposed to be provided with a foamed layer in order to impart the same texture and flexibility as natural leather.

Artificial leather, that is, a method of providing a fine foam layer in a wet method is to impregnate a fibrous base material with a water-miscible organic solvent such as dimethylformaldehyde of a polyurethane elastomer and then in a non-solvent such as water. A foamed layer (microporous layer) formed by solidifying with a known method is known.

The artificial leather obtained by the above-described wet method is preferable because the texture is similar to that of natural leather, but is expensive because the manufacturing process is complicated. In particular, when using woven fabrics and knitted fabrics that are rich in elasticity as the fibrous base material, very thin fabrics such as cold koji are used to suppress dimensional changes in processes such as impregnation, solidification, drying, and surface finishing. A complicated and uneconomic manufacturing method in which the fiber base material is used after being attached to the back surface and then peeled and removed must be employed.

On the other hand, as a method of providing the foam layer in the dry method, as previously proposed by the applicant,
There is a method in which a urethane prepolymer is prepared and foamed and cured in a humidified and heated atmosphere. Specifically, a urethane prepolymer having an isocyanate group at the terminal is reacted in a humidified and heated atmosphere to form a foamed layer, which is adhered to one surface of the polyurethane urea foam layer and the other surface. It is known that a fiber base material layer is provided via a layer to form a synthetic leather (Patent Document 1, etc.).

The synthetic leather obtained by the above method has a texture similar to that of natural leather and has been accepted by consumers. In addition, the manufacturing process is simple compared to artificial leather by a wet method, and furthermore, since the amount of organic solvent used is very small, it can be said to be an environmentally friendly manufacturing method.

JP 2000-5244 A

However, the synthetic leather obtained by the above method has a room for improvement although the manufacturing process is simple compared with the wet method. That is, in the above method, since the fibrous base material layer is laminated on one side of the foam layer via the skin layer and the other side via the adhesive layer, at least four layers need to be laminated. Further, since the adhesive layer is provided, a curing process of about 48 hours is required to completely cure the resin constituting the adhesive layer. If the release paper is peeled off without completing the curing of the resin that constitutes the adhesive layer, the resin may ooze out on the fabric of the fibrous base material, and the surface wrinkles may disappear. Will significantly degrade the surface appearance.
An object of the present invention is to provide a synthetic leather that has a foam layer formed by the dry method and has a simplified process than a conventional production method and does not require a curing period.

In the present invention, the composition of the resin constituting the foamed layer and the curing method were examined, and various studies were conducted on synthetic leather in which the foamed layer also served as the adhesive layer, that is, the adhesive layer was not provided.
The specific configuration of the present invention is as follows.
The synthetic leather of the present invention is a synthetic leather comprising at least a skin layer, a foamed layer, and a fibrous base material, and the foamed layer has an isocyanate group at the terminal, and the isocyanate group content is 2 to 6% by weight. After the urethane prepolymer is applied, 15-40% of the isocyanate groups of the urethane prepolymer are reacted in a heated atmosphere, and then the fibrous base material is bonded and humidified. A synthetic leather obtained by reaction-curing the remaining isocyanate groups in a heated atmosphere.

The synthetic leather of the present invention has a texture very similar to natural leather. In addition, since the foam layer serves as both the foam layer and the adhesive layer, the process is greatly simplified as compared with the conventional dry synthetic leather manufacturing method. Furthermore, since no adhesive layer is provided, a curing process is not required, and it is possible to produce a product immediately after molding.

  Hereinafter, the present invention will be described in detail.

The synthetic leather of the present invention is a synthetic leather comprising at least a skin layer, a foamed layer, and a fibrous base material, and the foamed layer has an isocyanate group at the terminal, and the isocyanate group content is 2 to 6% by weight. After the urethane prepolymer is applied, 15-40% of the isocyanate groups of the urethane prepolymer are reacted in a heated atmosphere, and then the fibrous base material is bonded and humidified. A synthetic leather obtained by reaction-curing the remaining isocyanate groups in a heated atmosphere.

First, the foam layer will be described. The foamed layer is made of a urethane prepolymer having an isocyanate group at the terminal and an isocyanate group content of 2 to 6% by weight.

The urethane prepolymer is obtained by reacting glycol and diisocyanate.
As the glycol constituting the urethane prepolymer, it is preferable to use a glycol mixture in which a long-chain glycol and a short-chain glycol are mixed. By using a glycol mixture in which a long chain glycol and a short chain glycol are mixed, a foamed layer having both flexibility and strength can be obtained.

As long chain glycol, polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol, polyoxypropylene / oxymethylene glycol, polyethylene glycol adipate, polybutylene glycol adipate,
Preference is given to glycols selected from polyneopentyl glycol adipate, polybutylene / hexylene glycol adipate, polycaprolactone, poly-3-methylpentanediol adipate, poly-β-methylvalerolactone, dimer acid diol, or mixtures thereof.
These long-chain glycols have a number average molecular weight of 1000 to 5000, particularly 1000 to 3
000 is preferred.

Short chain glycols include ethylene glycol, diethylene glycol, 1,3-butanediol, 1,4-butanediol, propylene glycol, dipropylene glycol, 3-methylpentanediol, 3,3-dimethyl-1,3-propanediol , A glycol selected from nonanediol, 2,4-diethyl-1,5-pentanediol, 3,3-dimethylolheptane, 2-ethyl-1,6-hexanediol, 2-methyl-1,3-propanediol, or Mixtures of these are preferred.
The short chain glycol has a molecular weight of 300 or less, and does not contain any halogen.
Those distances between the carbon atoms to number of hydroxyl group is bonded is C ₉ or less.

The long-chain glycol and the short-chain glycol are desirably mixed so as to have a number average molecular weight of 400 to 1800 to form a glycol mixture. The number average molecular weight of the glycol mixture is 7
More preferably, it is 00-1500. The number average molecular weight of the glycol mixture is 400
If it is less than 1, the hardness is likely to change even at a temperature around room temperature, and the texture of the synthetic leather may be impaired. On the other hand, when the number average molecular weight of the glycol mixture exceeds 1,800, the elongation at break of the resulting foamed layer tends to increase, so the tensile strength as a synthetic leather tends to decrease.

Although it does not specifically limit as diisocyanate which comprises a urethane prepolymer,
4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6
-Toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornane diisocyanate is preferred.

As a method for synthesizing a urethane prepolymer, a method in which heat-dissolved diisocyanate is continuously added to glycol and a solvent in a reaction vessel, or glycol, diisocyanate, and solvent are charged into a reaction vessel all at once and gradually stirred. The method of heating is mentioned.

The urethane prepolymer synthesized as described above has an isocyanate group at the terminal, and the content of the isocyanate group needs to be adjusted to be 2 to 6% by weight, preferably 3.5. -4.5 wt%. Isocyanate content is 2% by weight
If it is less than the above, the desired foamed state is not obtained. Conversely, if the isocyanate group content exceeds 6% by weight, the ratio of urea bonds tends to increase, and the texture becomes hard and unsuitable as a synthetic leather. In the present invention, by setting the isocyanate group content within the above range, it is possible to obtain a foamed layer that is moderately partially crosslinked and has a certain molecular weight.

The amount of the organic solvent used for the synthesis of the urethane prepolymer is preferably in the range of about 0 to 20 parts per 100 parts by weight of the total resin. If the amount of the solvent is too large, the viscosity is remarkably reduced, and moisture is contained in the urethane prepolymer solution. It becomes difficult to take in, and foaming property falls. The urethane prepolymer can be synthesized without using a solvent. However, in consideration of viscosity adjustment, storage stability, foamability and the like of the urethane prepolymer, the synthesis is easier when using the solvent.

A catalyst may be added to the urethane prepolymer solution. As the catalyst, it is desirable to use both a tin compound catalyst and an amine catalyst in combination.
As the tin compound catalyst, organic tin compounds such as tin octylate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dimaleate, dibutyltin mercaptide, dibutyltin oxide and tin acetylacetate can be used.
Examples of the amine catalyst include triethylamine, N, N-diethylcyclohexylamine,
N, N, N ′, N′-tetramethylethylenediamine, N, N, N ′, N′tetramethylpropane-1,3-propanediamine, N, N, N ′, N′-tetramethylhexamethylenediamine, N, N, N ′, N ″, N ″ -pentamethyldiethylenetriamine, N,
Tertiary amine compounds such as N, N ′, N ″, N ″ pentamethyldiethylenedipropylenetriamine, triethylenediamine, N-methylmorpholine, N-ethylmorpholine can be used.

In addition to the urethane prepolymer solution as necessary, pigments, antiblocking agents,
Antioxidants, ultraviolet absorbers, light stabilizers, hydrolysis inhibitors, antibacterial agents, antifungal agents and the like may be added.

The synthetic leather of the present invention is formed by coating the urethane prepolymer that forms the above foamed layer on the skin layer, and then bonding the fibrous base material. Curing of the urethane prepolymer that forms the foamed layer is performed by first adding 15 to 15 of the isocyanate groups of the urethane prepolymer under a heating atmosphere.
After reacting 40% (primary curing) and bonding the fibrous base material, the isocyanate group of the urethane prepolymer is completely reacted in a humidified heating atmosphere (secondary curing). By passing through such a two-stage curing process, it is possible to obtain a synthetic leather that has strong adhesion between the foamed layer and the fibrous base material and does not impair the texture without using an adhesive layer.

If the reaction of the isocyanate group of the primary curing urethane prepolymer is less than 15%, the fibrous base material is bonded with the foam layer hardly cured, so foaming to the fibrous base material. The soaking of the layer becomes too large and the texture of the resulting synthetic leather is impaired.
On the other hand, if it exceeds 40%, the adhesion between the foamed layer and the fibrous base material is weak and easy to peel off.

Any skin layer can be used as long as it is conventionally used for synthetic leather. Specifically, polyester polyurethane, polyether polyurethane, polycaprolactone polyurethane, polyester / polyether copolymer polyurethane,
Examples thereof include polyamino acid / polyurethane copolymer resins, non-yellowing polycarbonate polyurethanes obtained by reacting a polycarbonate diol component, a non-yellowing diisocyanate component, a low molecular chain extender and the like. Further, polyvinyl chloride or synthetic rubber may be mixed with the above polyurethane as long as various physical properties as synthetic leather are not impaired.

The above-mentioned polyurethane forming the skin layer uses methyl ethyl ketone, toluene, dimethylformamide or the like as a solvent, and if necessary, a colorant, a filler, a light stabilizer, an ultraviolet absorber,
Various additives such as antioxidants and flame retardants are added to form a one-component polyurethane solution.

For the skin layer, the one-component polyurethane solution is applied to a release coater such as a release paper on a knife coater, comma doctor, roll coater, reverse roll coater, rotary screen coater, gravure coater, or other appropriate means. It is obtained by coating and drying. The releasable carrier such as release paper may have a smooth surface, or may have a drawn pattern or the like. When a releasable carrier with a drawn pattern or the like is used, a synthetic leather can be obtained in which a design by the drawn pattern or the like formed by transferring the drawn pattern or the like of the releasable carrier appears.

As the fibrous base material used in the present invention, the fibrous base material used in the present invention includes synthetic fibers such as polyester, polyamide and polyacrylonitrile, natural fibers such as cotton and hemp, rayon, sufu and acetate. Any material may be used as long as it is conventionally used as a fibrous base material for synthetic leather, such as a knitted fabric, a woven fabric or a nonwoven fabric made of recycled fibers alone or a blended fiber thereof. Further, the fibrous base material may be raised or not raised.

The synthetic leather of the present invention uses a foamed layer made of the above specific urethane prepolymer, and has a two-stage curing method for the foamed layer, so that it firmly adheres to the fibrous base material without providing an adhesive layer, and Synthetic leather that does not impair the texture is obtained. Moreover, since the adhesive layer is not provided, a curing process for complete curing of the adhesive layer is not required, and the production efficiency is significantly improved.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited by these Examples.

<Example 1>
100 g of Crisbon NY331 (manufactured by DIC Corporation) is used as the skin layer, 20 g of Dirac black L1770 is used as the pigment, 10 g of propyl acetate, and 10 g of DMF. (Made by Co., Ltd.) was applied at a coating amount of 150 g / m ² and dried at a temperature of about 115 ° C. for 90 seconds.
A urethane prepolymer solution for forming a foam layer on the obtained skin layer was applied at a thickness of 0.3 mm, and the foam layer was placed in a heating oven at 50 ° C. for 100 seconds to remove isocyanate groups in the urethane prepolymer. After reacting 25% (primary curing), a fibrous base material (weft knitted fabric having a thickness of 1.0 mm made of polyester fiber made of multifilament processed yarn having a single yarn fineness of 4 denier (elongation in warp direction: 63%, weft) Direction elongation 75%)), pass through a heating and humidification oven at 110 ° C and 100% humidity, react the remaining isocyanate groups (secondary curing), peel off the release paper, and obtain a synthetic leather It was.
The composition of the urethane prepolymer solution forming the foam layer is as shown in Table 1.

<Example 2>
A synthetic leather was obtained in the same manner as in Example 1 except that the urethane prepolymer solution constituting the foam layer was changed.

<Example 3>
A synthetic leather was obtained in the same manner as in Example 1 except that the urethane prepolymer solution constituting the foam layer was changed.

<Example 4>
Place in an oven at 50 ° C. for 70 seconds to obtain 15 of the isocyanate groups of the urethane prepolymer.
Synthetic leather was obtained in the same manner as in Example 1 except that the primary curing was reduced to%.

<Example 5>
Place in an oven at 50 ° C. for 110 seconds to remove 3 of the isocyanate groups of the urethane prepolymer.
A synthetic leather was obtained in the same manner as in Example 1 except that the primary curing was reduced to 0%.

<Example 6>
Place in an oven at 50 ° C. for 130 seconds to remove the isocyanate group 4 of the urethane prepolymer.
A synthetic leather was obtained in the same manner as in Example 1 except that the primary curing was reduced to 0%.

<Example 7>
A synthetic leather was obtained in the same manner as in Example 1 except that the urethane prepolymer solution constituting the foam layer was changed.

<Comparative Example 1>
A synthetic leather was obtained in the same manner as in Example 1 except that the secondary curing was performed immediately without performing the primary curing.

<Comparative example 2>
Put it in an oven at 80 ° C. for 100 seconds to obtain 5 of the isocyanate groups of the urethane prepolymer.
A synthetic leather was obtained in the same manner as in Example 1 except that primary curing was performed to reduce 0%.

<Comparative Example 3>
A synthetic leather was obtained in the same manner as in Example 1 except that the urethane prepolymer solution constituting the foam layer was changed.

<Comparative example 4>
A synthetic leather was obtained in the same manner as in Example 1 except that the urethane prepolymer solution constituting the foam layer was changed.

The synthetic leather obtained in Examples 1 to 7 and Comparative Examples 1 to 4 was evaluated for adhesive strength and texture according to the following criteria. The evaluation is shown in Table 1.

<Adhesive strength>
About the obtained synthetic leather, adhesive strength (peeling strength) was evaluated according to JIS K6772. Specifically, the obtained synthetic leather is used as a test piece having a width of 30 mm and a length of 150 mm, and the coating composed of the skin layer and the foam layer and the fibrous base material are peeled off from the terminal by a length of 50 mm in parallel to the short side. Then, the peeled film and the fibrous base material are attached to a tensile tester (pendulum type tensile tester or a constant-limb extension type tensile tester with a self-recording device) and peeled off at a tensile speed of 200 mm / min. The adhesive strength was evaluated according to the broken part of the synthetic leather.
◎ ・ ・ ・ Destruction of material of foam layer ○ ・ ・ ・ Destruction at the interface of skin layer and foam layer △ ・ ・ ・ Destruction at the interface of fibrous base material and foam layer × ・ ・ ・ Adhesion of fibrous base material and foam layer Not

<Texture>
Sensory evaluation was performed about the texture of the obtained synthetic leather.
◎ ・ ・ ・ very good ○ ・ ・ ・ good × ・ ・ ・ bad

From the above examples, it can be seen that the synthetic leather of the present invention provides a synthetic leather excellent in adhesive strength and texture without providing an adhesive layer.

Claims (1)

A synthetic leather comprising at least a skin layer, a foam layer and a fibrous base material,
The foam layer is formed from a urethane prepolymer having an isocyanate group at the terminal and an isocyanate group content of 2 to 6% by weight. After the urethane prepolymer is applied, the urethane prepolymer is heated in a heated atmosphere. A synthetic leather obtained by reacting 15 to 40% of an isocyanate group of a polymer and then bonding a fibrous base material and reacting and curing the remaining isocyanate group in a humidified and heated atmosphere.